Biological Evolution

Describe Lamarck's theory of evolution

"Use and disuse of organs":When environments changed, organisms had to change their behaviour to survive. When an organism developed a need for a particular structure, this need induced the development of the structure. This was based on the observations that structures that are often used become well-developed whereas those that are not used tend to degenerate. For instance, Lamarck postulated that giraffes constantly stretched their necks to reach leaves at the top of trees, so their necks grew longer. "Inheritance of acquired characters": Beneficial characteristics, which were acquired during the lifetime of the individual, could be inherited by the offspring - this meant that evolutionary change could be achieved by the inheritance of acquired characteristics. In the case of the giraffes, the long-neck characteristic was passed on to the offspring.

Describe gene flow using examples of (a) Mosquito, (b) human population and (c) copper tolerance in grass plants

(a) Gene flow can also transfer alleles that improve the ability of populations to adapt to local conditions. e.g. spread of insecticide-resistance alleles (b) mating is more common between members of population that previously had very little contact, leading to an exchange of alleles and fewer genetic differences between those populations (c) It demonstrates gene flow opposing natural selection occurring on abandoned mine sites in Great Britain. The explanation relates to the reproductive system of this grass, in which pollen, the floral equivalent of sperm, is dispersed by wind. As a result, pollen grains (and the alleles they carry) can move great distances, leading to levels of gene flow between mine sites and unpolluted areas high enough to counteract the effects of natural selection.

What are the effects of genetic drift?

(a) Genetic drift is significant in small populations. Chance events can cause an allele to be disproportionately over- or underrepresented in the next generation. (b) Genetic drift causes random change of allele frequencies. Because of genetic drift, an allele may increase in frequency one year, and then decrease the next; the change from one year to the next is not predictable. Thus, unlike natural selection, genetic drift causes allele frequencies to change at random over time. (c) Genetic drift can lead to loss of genetic variation within populations and creates genetic divergence between populations. By causing allele frequencies to fluctuate randomly over time, genetic drift can eliminate alleles from a population. Because evolution depends on genetic variation, such losses can influence how effectively a population can adapt to a change in the environment. (d) Genetic drift can cause harmful alleles to become fixed. Alleles can be lost or become fixed entirely by chance through genetic drift. Alleles fixed by genetic drift are as likely to be harmful to the organism as to be beneficial or of no effect. When drift leads to the fixation of harmful alleles, the survival of a small population can be threatened.

How is maintenance of genetic variation within populations achieved?

(a) diploidy (b) balanced polymorphism (heterozygote advantage & frequency-dependent selection)

What are the processes that tend to reduce genetic variation within populations?

(a) genetic drift, (b) stabilizing selection (c) directional selection

What are the processes which contribute to abundant genetic variation in populations?

(a) mutations to generate new alleles, (b) sexual reproduction i.e. random fusion of gametes, and (c) crossing-over and independent assortment of homologous chromosomes during meiosis. The sexual recombination processes in (b) and (c) allows the variability introduced by mutation to be combined in new ways, which may be expressed as new phenotypes.

If a population of allopolyploids become established, what are outcomes of various selection pressures?

1. The new species may not compete successfully against species that are already established, so it becomes extinct. 2. The allopolyploid individuals may assume a new role in the environment and so coexist with both parental species. 3. The new species may successfully compete with either or both of its parental species. If it has a combination of traits that confers greater fitness than either or both parental species for all or part of the original range of the parent(s), the hybrid species may replace the parent(s).

Describe how allopolyploidy has occured in bread wheat.

1. The process may have begun with hybridization between two wheats, one the cultivated species T. monococcum (AA), the other one of several wild species that probably grew, as weeds at the edges of fields (BB). Chromosome sets A and B of the two species would not have been able to pair at meiosis, making the AB hybrid sterile through hybridization. 2. However, an error in cell division and self-fertilization would have produced a new species (AABB) with 28 chromosomes. Today, we know this species as emmer wheat (T. turgidum) 3. The cultivated emmer wheat, with its 28 chromosomes, hybridized spontaneously with the closely related wild species T. tauschii (DD), which has 14 chromosomes. 4. The hybrid (ABD, with 21 chromosomes) was sterile, but a cell division error in this hybrid and self-fertilization doubled the chromosome number to 42. The result was bread wheat, T. aestivum with two each of the three ancestral sets of chromosomes (AABBDD).

What are the 7 essential features of Darwin-Wallace's theory? (same for Neodarwinism)

1. organisms have great potential to reproduce 2. environmental restrictions/constancy in numbers 3. struggle for existence/survival 4. variation within a population 5. survival of the fittest by natural selection 6. Differential reproduction leading to reproductive success 7. formation of new species

What does a node in a phylogenetic tree represent?

A branch point where the tree splits The separation of one lineage into multiple distinct lineages The divergence of two or more species from a common ancestor

What is a clade?

A clade always consists of a group of species that share a single recent common ancestor. All species that descended from this ancestor are in the clade. Monophyletic group.

Describe the genetic species concept.

A genetically distinct group of natural population of organisms that share a common gene pool. This concept deals with the study of the genetics of speciation. It deals with genetic isolation: a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups. Application of this concept uses data from mitochondrial and nuclear genomes. The purpose is to identify species, to understand the extent to which the integrity of the gene pools is protected and the nature of hybridization (crosses between closely-related species, forming hybrids).

Describe monophyletic grouping.

A monophyletic taxon includes an ancestral species and all its descendants. Monophyletic taxa are natural groupings, because they represent true evolutionary relationships and include all close relatives. Sister taxa, or sister groups, share a more recent common ancestor with one another than either taxon does with any other group shown

Describe paraphyletic grouping.

A paraphyletic taxon contains a common ancestor and some, but not all, of its descendants.

Describe polyphyletic grouping.

A polyphyletic taxon consists of several evolutionary lines that do not share the same recent common ancestor. Systematists avoid constructing polyphyletic taxa, because they are unnatural and misrepresent evolutionary relationships. Such polyphyletic groupings are sometimes accepted temporarily until research provides additional data.

What is a species?

A species is the smallest independently evolving unit.

How can phylogeny be inferred using shared derived characters?

A suitable outgroup can be determined based on evidence from morphology, paleontology, embryonic development, and gene sequences. By comparing members of the ingroup to each other and to the outgroup, we can determine which characters were derived at the various branch points of vertebrate evolution.

What are the key points about points about phylogenetic trees and what they signify?

A: The sequence of branching in a tree does not necessarily indicate the actual (absolute) age of the particular species. we should interpret the diagram solely in terms of patterns of descent. No assumptions should be made about when a particular species evolved or how much genetic change occurred in each evolutionary lineage. B: A taxon on a phylogenetic tree does not evolve from the taxon next to / preceeding it. We can infer only that the lineage leading to wolves and the lineage leading to coyotes both evolved from the common ancestor at branch point

What is the definition of adaptation

Adaptation results from the accumulation of favourable genetic changes through natural selection, since organisms that are anatomically, behaviourally and physiologically well-suited to a specific environment are more likely to survive and reproduce. This differential survival and reproduction of organisms in a population that have an advantageous, heritable trait leads to an increase in the proportion of individuals in future generations that have the favourable trait and to a decrease in the proportion of individuals that do not. Adaptation also means that the distribution of traits in a population can change when conditions change. Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline (and sometimes the extinction) of some species.

What is multiple sequence alignment?

Align comparable sequences from the species being studied. If the species are very closely related, the sequences probably differ at only one or a few sites. In contrast, comparable nucleic acid sequences in distantly related species usually have different bases at many sites and may have different lengths. This is because insertions and deletions accumulate over long periods of time.

Describe the significance of nucleic acids (DNA/RNA) in molecular/biochemical homologies.

All forms of life use the same genetic language of DNA and RNA, and the genetic code is essentially universal. Thus, it is likely that all species descended from common ancestors that used this code. However, molecular homologies go beyond a shared genetic code. When an ancestral species gives rise to two or more descendants, these descendants will initially exhibit fairly high overall similarity in their DNA. However, as the descendants evolve independently, they will accumulate more and more differences in their DNA. Consequently, organisms that are more distantly related would be expected to accumulate a greater number of sequence differences in their DNA, whereas two species that are more closely related should share a greater portion of their DNA.

Describe how no natural selection leads to non-evolving populations.

All genotypes have equal *fitness. All genotypes must be equally adaptive and reproduce equally well. The number of offspring must be independent of genotype.

Describe the first essential feature of Darwin-wallace's theory. (organisms have great potential to reproduce) (same for Neodarwinism)

All organisms produce large numbers of offspring that, if they survived, would lead to a geometric increase in the size of any population. Observation I: tendency for production of large number of offspring

Describe how an allopolyploid arises and how it leads to speciation.

An ALLOPOLYPLOID contains more than two sets of chromosomes from two or more species. A hybrid between two species is normally sterile because its chromosomes are not homologous and cannot pair during meiosis. However, the hybrids may be able to reproduce asexually. 1. When haploid gametes from two different species combine, the resulting hybrid is normally sterile because its chromosomes cannot pair during meiosis. This is hybrid sterility, a form of physiological isolation that occurs as a post-zygotic barrier. 2. However, the hybrid may reproduce asexually, as many plants can do. 3. Subsequent errors in cell division may produce chromosome duplications that result in a diploid set of chromosomes (2n = 10). Now chromosomes can pair in meiosis, and haploid gametes will be produced; thus, a fertile polyploid species has formed. The new species has a chromosome number equal to the sum of the diploid chromosome numbers of its parent species. Hence, an allopolyploid (an interspecific hybrid) produced by allopolyploidy, reproduces with itself (self-fertilization) or with a similar individual. However, allopolyploids are reproductively isolated from both parents, because their gametes have a different number of chromosomes from that of either parent.

Describe how an autopolyploid arises and how it leads to speciation.

An AUTOPOLYPLOID contains more than two sets of chromosomes, all derived from a single species 1. A failure of cell division after chromosome duplication could double a cell's chromosomes through non-disjunction. This causes the formation of tetraploid (4n) cells for example in a particular plant species. 2. If one of this 4n cells gives rise to a tetraploid plant, flowers produced would have diploid gametes through meiosis. 3. If self-fertilization occurs, as it commonly does in plants, the resulting tetraploid zygotes would develop into plants that can produce fertile tetraploid offspring by self-pollination or by mating with other tetraploids. A tetraploid cannot, however, produce fertile offspring by mating with a parent plant. The fusion of a diploid (2n) gamete from the tetraploid plant and a haploid (n) gamete from the diploid parent would produce triploid (3n) offspring. Triploid individuals are sterile; they cannot produce normal gametes because the odd number of chromosomes cannot form homologous pairs and separate normally during meiosis. Thus, the formation of a tetraploid (4n) plant is an instantaneous speciation event: A new species, reproductively isolated from its parent species, is produced in just one generation.

What are homoplasies?

Analogous structures that arose independently

What is the relationship between analogy and convergent evolution?

Analogy refers to a characteristic that superficially appears homologous, but is actually independently acquired. This shows that such a similar structure in two or more species is not derived from a recent common ancestor; instead, it is usually due to adaptation to similar environments. This is a form of convergent evolution whereby similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages. Thus, analogous structures do not reflect evolutionary relationships between species.

Describe stage 2 of species formation.

Barrier develops: Subgroups of the ancestral species become divided, separated from one another by a barrier (geographical isolation / ecological isolation between populations that live within the same area) Members still can interbreed if brought together.

Describe stage 4 of species formation.

Barrier disappears: If the reproductive isolating mechanisms (RIMs) are sufficiently weak as to allow free interbreeding across the reunited populations, and such matings produce offspring that are not at some fitness disadvantage compared to offspring derived from matings between individuals from within either population, then the process of speciation halts and a single species remains. However, if the RIMs that developed during allopatric speciation put offspring from matings between two populations' individuals at a selective disadvantage, the process of speciation continues. Over time, they would diverge so substantially that they are reproductively isolated / genetically incompatible and are unable to produce fertile viable offspring, even if mating occurs. There must be accumulation of sufficient reproductive isolating mechanisms (RIMs), adaptations and genetic diversity for a new species to be formed. Where there was once a single species, now there are two.

Describe how diploidy leads to maintenance of genetic variation.

Because most eukaryotes are diploid, a considerable amount of genetic variation is hidden from selection in the form of recessive alleles. Recessive alleles that are less favourable than their dominant counterparts, or even harmful in the prevailing environment, can persist because they are propagated in heterozygous individuals. This latent variation is exposed to natural selection only when both parents carry the same recessive allele and combine two copies in one zygote. This happens only rarely if the frequency of the recessive allele is very low. The rarer the recessive allele, the greater the degree of protection from natural selection. Heterozygote protection maintains a huge pool of alleles that might not be favoured under present conditions but some of which could bring new benefits when the environment changes.

What is the bottleneck effect?

Bottleneck effect occurs when natural disasters, diseases, or predators (by This will result in the survivors representing a small random portion of the original gene pool. Alleles may be under-represented, over- represented or even eliminated. Even when the population increases to its original size, a portion of its original genetic diversity remains lostmay kill large numbers of individuals, causing drastic short-term reductions of a population size. Leads to reduction and restriction in genetic variability which may explain the problem with many endangered species.

Describe how no mutations leads to non-evolving populations.

By introducing or removing genes from chromosomes or by changing one allele into another, mutations modify the gene pool. In natural populations, the mutation rate varies considerably. Mutations are often spontaneous.

Describe how a large population leads to non-evolving populations.

Changes in the gene frequencies of large populations are less likely to occur by chance. In a small population however, the random loss of one or more individual genotypes can eliminate one or more alleles from the population.

What is the difference between characters and traits?

Characters can be any observable characteristics of organisms, for example they may be anatomical features, developmental or embryological processes, behavioral patterns, or genetic sequences. Coat colour, for instance, is a character. Traits, or character states, are the specific values of a character. "Brown coat" and "white coat" are possible traits for the coat colour character.

What does comparing the sequences of cytochrome c in different organisms tell us?

Cytochrome c is found in the mitochondria of every aerobic eukaryote — animal, plant, and protist. The amino acid sequences of many cytochrome c proteins have been determined, and comparing them shows that these proteins are related. We assume that each of the molecules of cytochrome c in different organisms has descended from a precursor cytochrome in a primitive microbe that existed over 2 billion years ago. In other words, these molecules are homologous. By determining the number of differences in the cytochrome c amino acid sequences in each organism, we could calculate the number of substitutions that have occurred per amino acid site. The number of amino acid residues that differ in homologous proteins from any two species is in proportion to the phylogenetic difference between those species.

What are the advantages of molecular methods in the study of evolutionary relationships? 9/9

Different genes evolve at different rates, even in the same evolutionary lineage. As a result, molecular trees can represent short or long periods of time, depending on what genes are used.

Describe stage 3 of species formation.

Differentiation due to different selection pressures: Gene flow between the geographically isolated populations is interrupted. Variation arising within one population is not shared with the other via interbreeding. This is important - interrupted gene flow means that each population is free to follow its own evolutionary destiny challenged by its unique set of environmental demands. Thus, the biological species concept uses the presence or absence of gene flow among populations to delineate species boundaries. each population experiences a slightly different environment that delivers different selective pressures. Different characters will be successful in each location. Through successive generations, the accumulation of character driven by local environmental conditions leads to the genetic distinctiveness of each separate population. Due to mechanisms of natural selection and changes in the gene pool, each population becomes more adapted to its own environment. Each population undergoes independent evolution, and if the barrier persists and enough time passes, the separate populations become genetically distinct.

What is directional selection?

Directional selection favours one extreme of the phenotype range, and shifts the population mean for the selected character. It acts to eliminate the other extreme phenotype and the alleles promoting this extreme become less frequent in the population. This type of selection usually follows a changing environment.

What is disruptive / destabilising selection?

Disruptive selection has the opposite effect of stabilizing selection. Instead of favoring intermediate phenotypes (those near the average value) and eliminating extreme phenotypes, it eliminates intermediate phenotypes and favors extreme phenotypes

How does disruptive selection lead to formation of new species?

Disruptive selection is important because it sometimes plays a part in speciation (the formation of new species). If small-beaked seedcrackers began mating with other small-beaked individuals, their offspring would tend to be small-beaked and would feed on small seeds. Similarly, if large-beaked individuals chose only other large-beaked individuals as mates, they would tend to produce large-beaked offspring that would feed on large seeds. The evolutionary significance of disruptive selection lies in the possibility that the gene pool may become split into two distinct gene pools. In this way, selection would result in two distinct populations. Under certain conditions over time, the populations may eventually form two new species.

Describe the order of taxa from the top to the bottom of the hierarchy.

Domain Kingdom Phylum (animals) = Division (plants) Class Order Family Genus Species

What does a tip in a phylogenetic tree represent?

Each branch tip shows the end point for a particular branch It represents a group of related organisms / taxon which is present today (e.g. modern species) or those that have become extinct All branch tips arising from a given node are descendants of the common ancestor at that node

Describe the significance of proteins in molecular/biochemical homologies.

Each of our proteins has a specific composition and number of amino acids arranged in a particular order. Any differences in the sequence reflect changes in the DNA sequence

What are mass extinctions and the factors that may cause them?

Each period of mass extinction has been followed by a period of adaptive radiation of some of the surviving groups. Major changes in climate could have adversely affected those plants and animals that lacked the genetic flexibility to adapt. Marine organism, in particular, are adapted to a steady unchanging environment. Changes in the environment due to catastrophes may also have also caused past mass extinctions. Biological factors can also trigger extinction. Competition among species may lead to the extinction of species that cannot compete effectively. The human species in particular has had a profound impact on the rate of extinction. The habitats of many animal and plant species have been altered or destroyed by humans, and habitat destruction can result in a species' extinction.

What is an ecological niche?

Ecological niche is the unique set of habitat resources that a species requires, as well as its influence on the environment and other species. Within their own niche, members of a given species compete with one another for survival. If two organisms are very similar, their needs will overlap, which results in competition. Such competing organisms are likely to be of the same species.

Describe ecological opportunities.

Ecological opportunities mean the availability of new or novel types of resources that have driven a wide array of adaptive radiations. Adaptive zones are ecological opportunities that were not exploited by an ancestral organism. When an adaptive zone is empty, a colonizing species will encounter no competitors, rapidly diversify that leads to efficient use of the available resources. The species develops adaptations that make them thrive. In the process of occupying the available adaptive zone, succeeding generations diversify into new species, leading to rapid speciation from the ancestral species.

What are the key ideas and conclusion from island biogeography?

Evidence to support evolutionary deductions based on homology: • Closely related species sharing similar characteristics tend to be found in the same geographic region • Island biogeography o Most island species are closely related to species from the nearest mainland or neighbouring island / islands tend to have larger proportions of endemic species Conclusion: • These species could have descended with modification from a common mainland ancestor

What are the key ideas and conclusion from the fossil evidence of the horses from north america?

Evidence to support evolutionary deductions based on homology: • Progressive changes in the structures of organisms as shown by the fossil record • Increase in complexity Conclusion: • Descent with modification through changes in homologous structures due to environmental selection pressures

Describe evolutionary novelties through morphological innovation.

Evolutionary novelties originate through modifications of pre-existing structures. New designs arise from structures already in existence. A change in the basic pattern of an organism produces something unique. Usually, these evolutionary novelties are variations of some pre-existing structures called preadaptation that originally fulfilled one role but subsequently changed in a way that was adaptive for a different role. In each case, the evolution of new morphological features is hypothesized to have supported rapid speciation and ecological divergence. Because islands have fewer species than do mainland areas of similar size, latitude and topography, vacant adaptive zones are more common on islands than on continents.

What are shared ancestral characters (plesiomorphies)?

Features that were present in an ancestral species and remain present in all groups descended from that more distant ancestor. As a result of descent with modification, organisms both share characteristics with and differ from their ancestors.

Describe Darwin-Wallace's theory of evolution (darwinism).

First, Darwin presented evidence to support his view that present-day species arose from a succession of ancestors. He called this evolutionary history of life "DESCENT WITH MODIFICATION". As the descendants of a remote ancestor spread into various habitats over millions and millions of years, they accumulated diverse modifications, or adaptations, that fit them to specific ways of life in their environment. Darwin's second main point proposed a mechanism for descent with modification, that is, by NATURAL SELECTION. It was so-called because the natural environment "selects" for certain traits to be propagated.

What is fitness?

Fitness is the relative reproductive success of individuals, within a population, in leaving offspring in the next generation.

Describe the founder effect using the example of the human amish population.

Fleeing from religious persecution, about 200 members of the Amish religion migrated from Switzerland to Pennsylvania between 1720 and 1770. Since that time, virtually all the Pennsylvanian Amish moved to Lancaster County and have remained reproductively isolated from non-Amish Americans. The population increased to about 8000 by 1964. In that year, geneticist Victor McKusick surveyed the Lancaster County Amish and discovered that they had an allele frequency for Ellis-van Creveld syndrome of about 0.07, compared with a frequency of less than 0.001 in the general population. Inbreeding among the Amish passed the allele along to their descendants:

Describe how comparing the sequences of cytochrome c across species is significant?

For example, all organisms have phenylalanine (F) at position 10, a histidine (H) at 18, a proline (P) at 30 and a methionine (M) at 80. Clearly, evolution selects against any change at these positions. In addition, numerous sites display a limited number of changes, in most cases allowing only residues with similar properties. His18 which coordinates to the heme iron, is conserved throughout. The implication is that the highly conserved residues (concensus sequences) contribute significantly to the structure and function of the protein. Other positions contribute very little and are highly variable. This implies a common and relatively recent evolutionary divergence. Information on the number of residue differences between homologous proteins of different species allows the construction of evolutionary trees that show the origin and sequence of appearance of different species during the course of evolution

Describe the significance of fossil/paleontological evidence in biological evolution.

Fossils are the preserved remains of once-living organisms typically left in sedimentary rocks. Layers of sedimentary rock are arranged in the order that they were deposited, with the most recent layers near the surface (unless they have been disturbed). The fossil record is rich in information. It broadly traces the history of life that is recorded by remains from the past; more specifically, allows us to study the history of particular groups and shows the evolutionary changes that have occurred over time in various groups of organisms. Evidence to support evolutionary deductions based on homology: • Greater variety of fossils in younger rocks • Emergence of new species and extinction of others Conclusion: • indicating the times at which species originated and became extinct

Describe placentals.

Found in other parts of the world but not Australia, except bats and some rodents (which arrived relatively recently). Young are born well-developed, completing embryonic development in the mother's uterus and can safely survive in the external environment (with varying degrees of parental care).

Describe marsupials.

Found only in Australia, evolved in isolation from the rest of the world. Young are born in a very immature condition and complete their embryonic development in a pouch, outside the mother's body until they are ready to emerge into the outside world.

What is the founder effect?

Founder effect occurs when one or few individuals colonize a habitat isolated from their place of origin or new to that species. The alleles they carry will be a significant fraction of the gene pool.

Describe how frequency-dependent selection preserves balanced polymorphism and maintain genetic variation.

Frequency-dependent selection is a type of balancing selection that maintains two different phenotypic forms in a population. In this form of selection, the relative fitness of different genotypes is related to how frequently they occur in the population. In frequency-dependent selection, the fitness of a genotype declines if it becomes too common in the population.

Describe gene flow in evolution.

Gene are exchanged with other gene pools as individuals move between them. Source of new genetic variation and tends to reduce differences between populations that have accumulated because of natural selection or genetic drift.

What are the effects of gene flow?

Gene flow among populations tends to reduce differences between populations that have accumulated as a result of natural selection or genetic drift. If it is extensive enough, gene flow can result in neighbouring populations combining into a single population with a common gene pool. Two significant effects of gene flow can be either: a. a constructive force if it spreads a beneficial mutation that arises in one population to other populations; or b. a constraining force if it impedes adaptation within a population by the continual flow of inferior alleles from other populations.

What is the definition of gene flow?

Gene flow is the movement of genes / alleles from one population to another. This may be achieved by the migration of fertile individuals from one population to another and breeding in that new population. A population may therefore gain or lose alleles by gene flow. Gene flow includes immigration and emigration.

What are the 4 evidence for biological evolution?

Homologies & Divergent Evolution Fossil Evidence Biogeography Direct Observations of Evolutionary Change

What is the relationship between homology and divergent evolution?

Homology refers to the presence, in two or more species, of a structure derived from a recent common ancestor (shared ancestry). Thus, homologous structures reflect evolutionary relationships between species. This is a form of divergent evolution whereby the presence of such a structure has allowed for the different species to evolve different functions in order to conquer different environments / habitats (e.g. in the air, land and water).

Describe how heterozygote advantage preserves balanced polymorphism and maintain genetic variation.

If individuals who are heterozygous at a particular gene locus have greater fitness than the homozygotes, they exhibit heterozygote advantage. sometimes natural selection will tend to maintain two or more alleles at that locus, hence helping to maintain genetic diversity.

Describe mate selection in evolution.

Individuals may not select their mate randomly and may seek out particular phenotypes, increasing the frequency of these " favoured" alleles.

How is the fifth essential feature of Neo-Darwinism different from that of Darwin's theory? (Survival of the fittest by Natural Selection)

Individuals with genetic variations best adapted to the new environment are more likely to survive to sexual maturity and reproduce. In other words, the environment or nature selects for pre-existing forms that are at a selective advantage.

What are the two forms of biogeography?

Island and continent biogeography

Describe island biogeography.

Islands generally have many species of plants and animals that are endemic, which means they are found nowhere else in the world. Species found on oceanic islands tend to resemble species of the nearest mainland, even if the environment is different. He also observed that species on oceanic islands do not tend to resemble species on islands with similar environments in other parts of the world. Darwin explained this observation by suggesting that islands are colonized by species from the nearest mainland. These colonists eventually give rise to new species as they adapt to their new environments. Such a process also explains why two islands with similar environments in distant parts of the world tend to be populated not by species that are closely related to each other, but rather by species related to those of the nearest mainland, where the environment is often quite different.

What are the advantages of the morphological species concept?

It can be applied to all organisms whether they are reproducing asexually or sexually. It can be useful even without information on the extent of gene flow. In practice, this is how scientists distinguish most species.

Describe the morphological species concept.

It characterizes a species by body shape and other structural features. Organisms are classified as the same species if their anatomical traits appear to be very similar. Likewise, microorganisms can be classified according to morphological characteristics at the cellular level.

What is the importance of classification?

It creates order out of chaos and helps in the study and referencing of organisms. It reveals natural evolutionary relationships and is a guide to the study of evolutionary pathways. It helps with the identification of newly discovered organisms. It forms a basis for an international system of nomenclature.

Describe the biological species concept.

It defines a SPECIES as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring with members of other populations. The members of a biological species are united by being reproductively compatible.

Describe the phylogenetic species concept.

It defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life . Members of a species descend from a common ancestor. Hence, they have a shared and unique evolutionary history. Through tracing morphological characteristics or molecular sequences.

What are the limitation of the ecological species concept?

It does not take into account the species' morphology and reproductive compatibility.

What is the definition of a population?

It is a group of individuals of the same species that live in a defined geographic area. The individuals of a population are capable of interbreeding (free to reproduce with any other individual) and producing fertile offspring. This group of individuals is considered as belonging to a sexually reproducing species, in which the individuals share a common gene pool. Random mating occurs in the population and therefore genes of individuals are free to mix within the gene pool. Thus, a population is the smallest unit that can evolve.

What is the definition of biological evolution?

It is defined as descent with modification through the mechanism of natural selection and refers to the cumulative changes that occur in a population from generation to generation over time. This leads to differences in populations and explains the origin of all the organisms that exist today or have ever existed. It encompasses both microevolution and macroevolution.

What is adaptive radiation?

It is evolutionary diversification of many related species from one or a few ancestral species in a relatively short period of time.

What are uniform / background extinctions?

It is the continuous, low-level extinction of species. Members of taxonomic groups are lost gradually over long time periods without abrupt loss of large numbers.

What is extinction?

It is the end of a lineage and occurs when the last individual of a species dies. The lost is permanent. Once a species goes extinct, it never reappears. Extinctions have occurred continually since the origin of life; by one estimate, only 1 species is alive today for every 2000 that have become extinct. Extinction is the eventual fate of all species, in the same way that death is the eventual fate of all individual organisms.

What is the definition of speciation?

It is the evolution / origin of species. Evolution occurs whenever the inherited characteristics of a population or of a species change over a period of time. When these changes lead to the formation of one or more new species, speciation has taken place.

What is the definition of microevolution?

It is the form of evolutionary change that involves small-scale evolutionary change within the species level. It is caused by changes in allele or genotype frequencies that occur within a population of a particular species over a few generations. Microevolution is the evolutionary event seen close up, and zoomed in; we are concerned with patterns of change within a population or species. It is also a short-term perspective. Changes in allele frequencies in or between populations are examples of microevolution.

What is macroevolution?

It is the large-scale evolutionary events over geological times. Macroevolution results in phenotypic changes in populations that are significant enough to warrant their placement in taxonomic groups at species level and higher. It involves the descent of different species from shared ancestors over many generations. Macroevolution is an evolutionary event seen zoomed back, the overall pattern; the origin of species and higher-level taxa, such as families or classes, are the concerns of macroevolution. It is also a long-term view, attending to such phenomena as the rise, diversification and demise of dinosaurs; the origin of birds; and the appearance of mammals.

What is phylogeny?

It is the organization of species according to particular characteristics which takes into consideration the evolutionary relationship between species. Phylogeny reflects evolutionary history and represents a hypothesis about patterns of evolutionary relationships among species. It showcases the branching relationships of organisms as they give rise to multiple descendant species over evolutionary time.

What is biogeography?

It is the study of the range and geographical distribution of extinct and modern species of organisms in different places throughout the world. The geographic distribution of organisms is influenced by many factors including continental drift, the slow movement of Earth's continental plates over time. It yields clear evidence for evolution for not only new species but also new genera and families of organisms that are formed.

What is biodiversity?

It is the variety of living organisms (i.e. distinct biological species) and their range of behavioural, ecological, physiological and other adaptations in an area such as an ecosystem.

What are the limitations of the morphological species concept?

It may be difficult to decide how many morphological characters to consider when characterizing individuals. It is difficult to analyze quantitative traits that vary in a continuous way among members of the same species. Researchers often disagree about how much morphological difference is necessary to separate different species. Members of the same species sometimes look very different and con- versely, members of different species sometimes look remarkably similar to each other.

Describe the Hardy-Weinberg Equilibrium / Principle.

It states that the frequencies of alleles and genotypes in a population′s gene pool remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work. This model describes a gene pool whose various allele frequencies are at equilibrium under certain conditions. It predicts genetic equilibrium (non-evolution). Such equilibrium is rarely attained in natural populations but it is a good starting point for explaining how gene pools change.

Describe the ecological species concept.

It views a species in terms of its ecological niche that is within its native environment, focusing on unique adaptations to particular roles in a biological community. Species from different evolutionary branches may come to resemble one another if they have the same ecological niche - result of convergent evolution. Species which are distributed over a wide geographical range or have occupied well- separated geographical habitats for a long period of time may show considerable phenotypic differences - result of divergent evolution.

Describe how chromosomal aberrations lead to genetic variation in a gene pool.

Key potential source of variation are the duplication of genes due to errors in meiosis (such as unequal crossing over) and slippage during DNA replication. Duplications of large chromosome segments, like other chromosomal aberrations, are often harmful, but the duplication of smaller pieces of DNA may not be. Gene duplications that do not have severe effects can persist over generations, allowing mutations to accumulate. The result is an expanded genome with new genes that may take on new functions.

What are the five condition for non-evolving populations (Hardy-Weinberg)?

Large population Random mating No migration / no gene flow No mutations occur No natural selection occurs

Describe allopatric speciation.

Long and slow process It refers to the formation of new species when one population becomes geographically separated from the rest of the species and subsequently evolves by natural selection and / or genetic drift. Any physical barrier that prevents individuals of different populations from meeting will inevitably prevent them from interbreeding, i.e. block gene flow. More likely to occur if the original isolated population is small. The different selection pressures of the new environment to which the population is exposed further accentuate the divergence caused by genetic drift.

Describe how balanced polymorphism leads to maintenance of genetic variation.

Many species of organisms have two or more forms that are genetically distinct from one another, but which are contained within the same interbreeding population. This condition is known as POLYMORPHISM. In transient polymorphism, one form is gradually replaced by the other. Selection itself may preserve variation at some gene loci. Balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population, a state called BALANCED POLYMORPHISM.

Describe the early embryonic development in biological evolution.

Many vertebrates contain structures with reduced or no functions that resemble functional structures of other vertebrates, suggesting that the structures are inherited from a common ancestor. Comparing early stages of development in different animal species reveals additional homologies not visible in adult organisms. At some time during development, all vertebrates bear striking anatomical similarities: they all have a post anal tail and exhibit paired pharyngeal (throat) pouches. These temporary similarities are called developmental homologies.

What is the link between microevolution and macroevolution.

Mechanisms that bring about microevolution like natural selection, mutation, genetic drift and gene flow account for not only the genetic variation within populations but also the origin of new species and higher taxa as well. Mass extinctions create new ecological opportunities that can be exploited by surviving organisms (which possess evolutionary novelties) to evolve, and bring about rapid adaptive radiations forming many descendant species within a short period of time. Macroevolution thus occurs as a result of microevolution and macroevolution cannot take place without microevolution.

Describe directional selection using the example of methicillin-resistant S. aureus (MRSA).

Methicillin works by deactivating a protein that bacteria use to synthesize their cell walls. However, S. aureus populations exhibited variations in how strongly their members were affected by the drug. In particular, some individuals were able to synthesize their cell walls using a different protein that was not affected by methicillin. These individuals survived the methicillin treatments and reproduced at higher rates than did other individuals. some MRSA strains are resistant to multiple antibiotics-probably because bacteria can exchange genes with members of their own and other species. Thus, the present-day multidrug-resistant strains may have emerged over time as MRSA strains that were resistant to different antibiotics exchanged genes. 1. Natural selection is a process of editing, not a creative mechanism. A drug does not create resistant pathogens; it selects for resistant individuals that are already present in the population. 2. Natural selection depends on time and place. It favors those characteristics in a genetically variable population that provide advantage in the current, local environment. What is beneficial in one situation may be useless or even harmful in another.

Describe the bottleneck effect using the example of greater prairie chick in US.

Millions of greater prairie chickens (Tympanuchus cupido) once lived on the prairies of Illinois. As these prairies were converted to farmland and other uses during the 19th and 20th centuries, the number of greater prairie chickens plummeted The few surviving birds had low levels of genetic variation, and less than 50% of their eggs hatched, compared to much higher hatching rates of the larger populations in Kansas, Nebraska, and Minnesota. These data suggest that genetic drift during the bottleneck may have led to a loss of genetic variation and an increase in the frequency of harmful alleles. To counteract possible negative effects of genetic drift, the researchers added a total of 271 birds from neighbouring states to the Illinois population over four years. This strategy succeeded. New alleles entered the population, and the egg-hatching rate improved to over 90%.

Describe the modern theory of evolution (the modern synthesis/neo-Darwinism).

Modern Synthesis incorporates principles of Mendelian genetics and knowledge of molecular biology, e.g. mutations and allele frequency changes, which were unknown to Darwin when he published his theory in 1859

What are the advantages of molecular methods in the study of evolutionary relationships? 1/9

Molecular data is genetic. Anatomical, behavioural, and physiological traits often have a genetic basis, but the relationship between the underlying genes and the trait may be complex. Nucleic acid and amino acid sequence variation has a clear genetic basis that is easy to interpret.

What are the advantages of molecular methods in the study of evolutionary relationships? 5/9

Molecular data is quantifiable. Nucleic acid and amino acid sequence data is precise, accurate, and easy to quantify, which facilitates the objective assessment of evolutionary relationships.

What are the advantages of molecular methods in the study of evolutionary relationships? 6/9

Molecular data often provides information about the process of evolution.

Describe the use of molecular/biochemical homologies in biological evolution.

Molecular evidence for evolution includes the universal genetic code and the conserved sequences of nucleotides in DNA/RNA and amino acids in proteins. Demonstrates evolutionary relatedness amongst different organisms

What are the advantages of molecular methods in the study of evolutionary relationships? 8/9

Molecular methods allow us to reconstruct phylogenies among groups of present-day prokaryotes and other microorganisms for which we have no fossil record at all. Molecular biology has helped to extend systematics to evolutionary relationships far above and below the species level, ranging from the major branches of the tree of life to its finest branches.

What are the advantages of molecular methods in the study of evolutionary relationships? 3/9

Molecular methods can be applied to a huge amount of genetic variation. An enormous amount of data can be accessed by molecular methods. The human genome, for example, contains more than 3 billion base pairs of DNA, which constitutes a large pool of information about our evolution.

What are the advantages of molecular methods in the study of evolutionary relationships? 2/9

Molecular methods can be used with all organisms. All living organisms possess nucleic acids and proteins, and so molecular data can be collected from any organism.

What are the processes that contribute to genetic variation in populations?

Mutations to generate new alleles Crossing-over and independent assortment of homologous chromosomes during meiosis Sexual reproduction

What is the definition of natural selection?

NATURAL SELECTION is the process by which the environment or nature selects for those well-adapted individuals with inherited traits that are best suited to the local environment. These selected individuals, possessing the selective advantage, are more likely to survive to maturity and reproduce, thus more likely to leave more offspring, than less fit / poorly adapted individuals. It increases the frequency of favourable genotypes / alleles in the gene pool, and the resultant population becomes adapted to its particular environment.

What are the three main mechanisms that can cause allele and genotype frequency change?

Natural selection (produces adaptive evolutionary changes as only in such a selection does the result depend on the nature of the environment) Genetic drift Gene flow

How is the seventh essential feature of Neo-Darwinism different from that of Darwin's theory? (Formation of new species)

Natural selection alone is not adequate to explain how new species are formed. The formation of a new species or speciation can happen only if populations are separated so that they DO NOT INTERBREED. The separated populations adapt to their own particular environments and may diverge, eventually forming new species over a very long period of time through reproductive / genetic isolation. This is known as the Speciation Theory.

Describe sympatric speciation.

Occurs rapidly and in a short time a new species evolves within the same geographic region as the parental species OR geographically overlapping population(s). The divergence of two populations in the same geographic range oc- curs when reproductive isolating mechanisms evolve at the start of the speciation process. Sympatric speciation occurs in at least two ways: ➢ Polyploidy i.e. change in ploidy level (the number of chromosome sets making up an organism's genome); ➢ Ecological isolation.

Describe stabilising selection using the example of sickle cell anaemia.

One might expect the allele HbS to be selected against and eventually eliminated from the human populations. However the distribution of the allele coincides with that of malaria (very high in malaria-infested Africa). Heterozygotes (HbAHbS) are more tolerant to malaria than homozygotes of the normal allele (HbA). There are therefore 2 conflicting selection pressures acting on the mutant allele HbS in malaria-prone regions: 1. A strong selection pressure against the allele in the homozygous condition (HbSHbS) which results in sickle-cell anaemia 2. A strong selection pressure for the allele in the heterozygous condition (HbAHbS), as the normal allele in the homozygous condition (HbAHbA) has a selective disadvantage in malaria-infested regions. Therefore the situation selects for the heterozygotes, which are fitter than either of the homozygotes, is known as heterozygote advantage. The action of the two opposing selection pressures thus retains the sickle-cell allele in the human population

Describe allopatric speciation using the example of Galapogos Finches.

One of the islands was colonized by a small population of finches from South America. This was a very rare event and the colonists were very few in number. Natural selection resulted in adaptations to local conditions on the island and reproductive isolating mechanisms (RIMs). Geographical isolation permitted additional speciation. Later, a few individuals of this island species reached neighbouring islands. After diverging on one of these other islands, a new species re colonized the island from which its founding population emigrated, and co-existed there with its parent species. Due to the mechanisms of natural selection and changes in the gene pool, each population of finches became more adapted to its own environment on one of the different islands. Due to various food sources available on the different islands, different bills had different selective advantage, and were selected differentially on different islands.

What are the advantages of the biological species concept?

One strength of the biological species concept is its focus on reproductive barriers, which directs our attention to how speciation occurs: by the evolution of reproductive isolation. Such analysis can distinguish groups of individuals that are sufficiently different to be considered separate species and is thus particularly valuable for studying how species originate.

Describe the seventh essential feature of Darwin-wallace's theory. (formation of new species )

Over many generations, the proportion of individuals possessing the advantageous traits increases whereas the proportion of those lacking the characteristics decreases, leading to evolution of the population. The inheritance of one characteristic alone may lead to the formation of a new subspecies / breed / variety / strain but not the formation of a new species. It is the accumulation of modifications and adaptations that may bring about a new species. A new species is formed only after the development and accumulation of several characteristics and adaptive mechanisms in a particular population over many generations. Described as the origin of species or speciation.

Describe immigration in evolution.

Population can gain alleles when they are introduced form other gene pools (gene flow)

What are postzygotic barriers and their examples.

Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult. Postzygotic barriers occur when prezygotic ones are overcome. They are mechanisms that create sterile hybrids. Types of post zygotic barriers: - physiological isolation - hybrid breakdown

What are prezygotic barriers and their examples.

Prezygotic barriers impede mating between species or hinder the fertilization of ova if members of different species attempt to mate. Such mechanisms are those that prevent formation of zygotes by blocking fertilization. Types of prezygotic barriers: - habitat isolation - temporal isolation - behavioural isolation - physiological isolation

Describe how polyploidy leads to sympatric speciation.

Reproductive isolation occurs in a single generation when a polyploid species with more than two sets of chromosomes arises from diploid parents.

What is the definition of homologous structures?

Same set of bones that are modified to allow vertebrate to perform different functions and to conquer different environments. Descent with modification through natural selection by shared/common ancestry

Describe behavioural isolation as a prezygotic barrier.

Sexual attraction between males and females of different animal species is limited due to differences in behaviour or physiology.

Describe stage 1 of species formation.

Single population: All members of the species actually or potentially interbreed and are reproductively / genetically isolated from other species.

What is convergent evolution?

Species from different evolutionary branches may come to resemble each other if they have similar ecological roles and natural selection has shaped similar adaptations.

Describe temporal isolation as a prezygotic barrier.

Species have different mating or flowering seasons or times of day, or become sexually mature at different times of the year. Different flowering times in plants may mean that cross-pollination is impossible. These are both examples of seasonal isolation.

Describe habitat isolation as a prezygotic barrier.

Species may occupy different habitats, so they never come in contact with each other.

Describe mutations in evolution.

Spontaneous mutations can develop that alter the allele frequencies of the gene pool and even create new alleles. Original source of genetic variation that provides new material for natural selection.

What is stabilising selection?

Stabilizing selection favours the existing mean and both extremes are selected against / eliminated, leading to a reduction in variance and favouring intermediate phenotypes. This type of selection is typical of an unchanging environment where competition is not severe. In effect, stabilizing selection is operating to prevent deviations away from this middle range of values. It does not change the most common phenotype of the population, but rather makes it even more common by eliminating extremes.

What are the advantages of phylogenetic species concept?

Such analysis can distinguish groups of individuals that are sufficiently different to be considered separate species. Phylogenetic information sometimes reveals the existence of "sibling species": species that appear so similar that they cannot be distinguished on morphological grounds. Scientists can then apply the biological species concept to confirm the phylogenetic distinction is confirmed by reproductive incompatibility.

Why can evolutionary relationships be inferred by analysing synapomorphies?

Synapomorphies identify evolutionary branch points. The process called speciation starts when two populations become genetically isolated, meaning that gene flow is reduced or absent. When genetic isolation occurs and species begin evolving independently, some of the homologous traits in each population undergo changes due to mutation, natural selection, and genetic drift. These changed traits are synapomorphies that identify the populations belonging to the two independent, descendant lineages Synapomorphies are nested. As you move through time and trace a tree from its root to its tips, each branching event adds one or more shared, derived traits

Describe hybrid breakdown as a post zygotic barrier.

The Fl interspecies hybrid is viable and fertile, but succeeding generations (F2, etc.) become increasingly inviable. This is usually due to the formation of less fit genotypes by genetic recombination.

What are the advantages of molecular methods in the study of evolutionary relationships? 7/9

The database of molecular information is large and growing. The large database of DNA and amino acid sequences can be used for making comprehensive evolutionary comparisons between many groups of organisms.

What are the limitations of phylogenetic species concept?

The difficulty is in determining the degree of difference required to indicate separate species.

Describe continent biogeography.

The evolution of major animal groups is also correlated with known changes in the distribution of land masses on the Earth. The first placental mammals, which have long internal gestation and give birth to offspring that are well developed, evolved after continental drift separated Australia from the other continents through continental drift

Describe homologous structures and homology in biological evolution.

The evolutionary relationships between species are determined mainly by structural / anatomical similarities in homologous structures, which suggest that they all descended from a common ancestor with that feature. Such a condition is known as homology which is the similarity in characteristics resulting from a shared ancestry.

What are the advantages of molecular methods in the study of evolutionary relationships? 4/9

The molecular approach helps us to understand phylogenetic relationships that cannot be determined by non-molecular methods such as comparative anatomy. All organisms have certain molecular traits in common, such as ribosomal RNA sequences and the amino acid sequences of some fundamental proteins. These molecules offer a valid basis for comparison among all organisms.

Describe how no gene flow leads to non-evolving populations.

The net movement of individuals between populations (either by immigration or emigration) must not be extensive enough to change gene frequencies. In natural populations the degree of migration varies considerably.

What are the limitations of the biological species concept?

The number of species to which this concept can be usefully applied is limited. (a) no way to evaluate the reproductive isolation of fossils (b) The biological species concept also does not apply to organisms that reproduce asexually all or most of the time, such as prokaryotes and self-fertilizing species (hermaphrodites). (c) In the biological species concept, species are designated by the absence of gene flow. There are, however, many pairs of species that are morphologically and ecologically distinct, but yet gene flow occurs between them forming rare hybrids between different species. (d) Some individuals of the same species rarely interbreed

Describe directional selection using the example of industrial melanism (peppered moth).

The peppered moth (Biston betularia) has two main forms, black melanic form (mutant) and pale / light / white form (wild-type) The moth flies at night and rests by day on tree trunks. This increase in frequency of black melanic forms, which was linked to industrialization, is thus called INDUSTRIAL MELANISM • In unpolluted areas with lichen-covered trees, the pale / light form had a selective advantage of being camouflaged by the lichens on the trees. • In the polluted areas with soot-blackened trees, the melanic / black form had a selective advantage. • He concluded that BIRDS EXERTED THE MAIN SELECTION PRESSURE by feeding on moths differentially, depending on the colour of the background environment.

What is the definition of genetic drift?

The random change of allele and genotype frequencies, as a result of chance alone, can differ from generation to generation in a small gene pool / population. This phenomenon is known as genetic drift. There are two forms of genetic drift: (a) founder effect and (b) bottleneck effect.

What is the definition of genotype frequency?

The relative proportion of a particular genotype present in a population.

What is the definition of allele frequency?

The relative proportion of the alleles of a gene present in a population.

Describe the fourth essential feature of Darwin-wallace's theory. (variation within a population)

The sexually produced offspring of an individual organism show individual variations such that no two offspring are identical. Such variations are absolute pre-requisites for evolution by natural selection. These variations occur spontaneously before a change in the environment. They are NOT formed as a result of the new environment to make the individuals better adapted. The environment merely selects those individuals that happen by chance to be better adapted. Observation III: variation in structure and behaviour within a population

What is analogy?

The similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait

What is the definition of a gene pool?

The total collection of all genes (i.e. all the alleles at all gene loci) of all breeding individuals (represented by their gametes) in a population at any one time. Dynamic Each population has a gene pool

What is divergent evolution?

The tracing of a species back to the common ancestor can indicate how these organisms have diversified and diverged to colonize the different environments.

How is the fourth essential feature of Neo-Darwinism different from that of Darwin's theory? (Variation within a population)

The variations within a population arise as a result of spontaneous mutations and not in response to the needs of the individuals. Variation is controlled by genes.

Describe how random mating leads to non-evolving populations?

This indicates that there is no tendency for certain genotypes to mate with other specific genotypes. If individuals preferentially choose mates with certain genotypes, including close relatives (e.g. inbreeding), random mixing of gametes does not occur.

What is coevolution?

This process in which species mutually affect one another's evolution. Predator-prey relationships

Describe the sixth essential feature of Darwin-wallace's theory. (Differential reproduction leading to reproductive success)

Those that survive to breed are likely to produce offspring similar to themselves. The advantageous traits that give them the edge in the struggle for existence are likely to be passed on to the next generation. The result would be adaptation. Observation IV: like produce like

Why do adaptive radiations occur?

Two general mechanisms can trigger adaptive radiations: (a) new resources (ecological opportunities) and (b) new ways to exploit resources (evolutionary novelties).

What are vestigial structures?

Vestigial structures are those that have no apparent function but they resemble structures present in their ancestors. When they have no clear function and they are no longer subject to natural selection, they will remain unchanged through a lineage. It is sometimes argued that some vestigial organs are not truly vestigial, i.e. they may perform some small function. While this may be true in some cases, the features can still be considered vestigial if their new role is a minor one, unrelated to their original function.

What are shared derived characters (synapomorphies)?

When two populations become separated and begin to evolve independently, some of their homologous traits change as a result of mutation, natural selection, and genetic drift. Shared derived characters originate in a recent common ancestor and are present in its descendants. Species that share derived characters form a CLADE. Systematists use shared derived characters to identify points where groups diverged from one another

How is the sixth essential feature of Neo-Darwinism different from that of Darwin's theory? (Differential reproduction i.e. like produces like)

With each succeeding generation, the proportion of individuals who possess the favourable genes / alleles and are at a selective advantage increases while the proportion of those at a selective disadvantage decreases. This would lead to changes in allele and genotype frequencies, and over a long period oftime, it could lead to evolutionary changes.

What can the number of mutations in molecular sequence tell us?

Within a given taxonomic group, mutations are assumed to have occurred at a fairly steady rate over millions of years. Thus, if more differences occur in homologous DNA sequences of one species compared to those of another, more time has elapsed since the two species diverged from a common ancestor

What is a taxon?

a formal grouping of organisms at any given level, such as species, genus, or phylum. Moving down the taxonomic ranks, there is: • decreased number of organisms • increased similarities amongst organisms within each taxon

What is the definition of adaptation?

an evolutionary modification that improves the chances of survival and reproductive success in a given environment.

What are the limitations of the genetic species concept?

common gene pool and common karyotypes of a species may change due to: - directional selection following changes in the environment, and - interbreeding between two different species.

How is the distance between species or population measured?

count up the number of base pair differences and to use this tally as the molecular distance between the two species. (can be for nucleotide or amino acid sequences)

Describe how meiosis and sexual reproduction leads to genetic variation in a gene pool.

crossing over at prophase I of meiosis, independent assortment of chromosomes at metaphase I of meiosis, and fertilization of gametes During meiosis, homologous chromosomes, one inherited from each parent, trade some of their alleles by crossing over. These homologous chromosomes and the alleles they carry are then distributed at random into gametes. Then, because myriad possible mating combinations exist in a population, fertilization brings together gametes that are likely to have different genetic backgrounds

What are some examples of vestigial traits in humans?

ear-wiggling muscles tail appendix wisdom teeth

Why does similarity of organisms alone not necessarily correlate with their evolutionary relatedness?

evolutionary change is not constant in rate and direction.

Describe disruptive selection using the example of beak size in black-bellied seed crackers.

individuals with either very short or very long beaks survive best and that birds with intermediate phenotypes are at a disadvantage. In this case, the selection pressure is food. At a study site in south-central Cameroon, West Africa, a researcher found that only two sizes of seed are available to the seedcrackers: large and small. - Birds with small beaks crack and eat small seeds efficiently. Birds with large beaks handle large seeds efficiently. - But birds with intermediate beaks have trouble with both, so alleles associated with medium-sized beaks are subject to purifying selection. Disruptive selection maintains high overall variation in this population.

What is an outgroup?

is a species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes all the species we are studying

Describe geographical barriers in evolution.

isolate the gene pool and prevent regular gene flow between populations

What is the significance of the Hardy-Weinberg principle?

microevolution can be detected by noting deviations from the Hardy-Weinberg equilibrium of the allele and genotype frequencies in the gene pool of a population. Such deviations suggest that one or more of the five conditions is/are NOT occurring in a population.

Describe the second essential feature of Darwin-wallace's theory. (environmental restrictions/constancy in numbers) (same for Neodarwinism)

most populations actually maintain relatively constant numbers. This is due to the limited resources available such as food, water, light, appropriate habitat, presence of diseases and unfavourable environmental conditions. Majority of offspring die before they reach sexual maturity. Observation II: limited resources

Describe physiological isolation as a postzygotic barrier.

o Hybrid inviability: The egg of one species is fertilized by the sperm from another species, but the fertilized egg fails to develop past the early embryonic stages. o Hybrid sterility: The interspecies hybrid survives, but it is sterile.

Describe physiological isolation as a prezygotic barrier.

o Mechanical isolation: Morphological features such as size and incompatible genitalia may prevent two members of different species from interbreeding. o Gametic isolation: Gametic transfer takes place, but the gametes fail to unite with each other. This can occur because the male and female gametes fail to attract, because they are unable to fuse, or because the male gametes are inviable in the female reproductive tract of another species.

What is the significance of gene mutations in the gene pool?

random mutations within pre-existing genes are a source of new alleles that are new heritable variations on which other evolutionary processes can act. It is important to understand that mutations are not goal- directed, as they do not arise as a result of, or in anticipation of, environmental necessities. The mutation from one allele to another can obviously change the allele frequency in the gene pool of a population. Mutations are rare and slow, so they have little effect on the Hardy-Weinberg equilibrium. Nonetheless, beneficial mutations are the only source of genetic variation that makes evolution possible.

Describe the fifth essential feature of Darwin-wallace's theory. (survival of the fittest by natural selection)

some will be better- adapted (fitter) to survive in the struggle for existence. These are more likely to survive long enough to breed. Inference II: survival of the fittest by natural selection

What is biological classification of living organisms

the act of systematically arranging organisms into groups based on particular shared characteristics (mainly morphology) and their similarities. It may not take into consideration evolutionary relationship between species.

What are the advantages of the ecological species concept?

the ecological species concept can accommodate asexually reproducing as well as sexually reproducing species. According to this concept, species are formed because evolutionary mechanisms control how each type of species uses resources. This species concept is particularly useful in distinguishing between bacterial species that reproduce asexually.

What is reproductive isolation?

the existence of biological factors (barriers) that impede members of two species from producing viable, fertile hybrids. These barriers are known as REPRODUCTIVE ISOLATING MECHANISMS (RIMs). Prezygotic barriers and postzygotic barriers.

Describe the third essential feature of Darwin-wallace's theory. (struggle for existence/survival) (same for Neodarwinism)

with more individuals than the environment can support, competition is inevitable. Organisms thus face a constant struggle for existence in an effort to survive. Only a few individuals will survive to reproduce in each generation. Inference I: competition