BIO FINAL 1050: CHP 13
What are the five micro-evolutionary processes?
1. Genetic Mutation (chance) ● Increases genetic variation and the rate is slow ● Mutations can change the meaning of genes 2. Genetic Drift (chance) ● The frequencies of alleles will be more stable from one generation to the next when a population is large. In a process called genetic drift, chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next. The smaller the population, the more impact genetic drift is likely to have. ● Earthquakes, floods or fires may kill large numbers of individuals, leaving a small surviving population that is unlikely to have the same genetic makeup as the original population. Such a reduction in population size is called the bottleneck effect. ● Genetic drift is also likely when a few individuals colonize an island or other new habitat, producing what is called the founder effect. The smaller the group, the less likely the genetic makeup of the colonists will represent the gene pool of the larger population they left. ● Sampling of gene pool is small→ decline of genetic diversity 3. Gene flow ● Effect of migration→ allele frequencies in a population can also change as a result of gene flow, where a population may gain or lose alleles when fertile individuals move into, or out of a population, or when gametes are transferred between populations. 4. Non-random mating (selection) ● Can do it visually 5. Natural Selection ● Populations consist of varied individuals, and some variants leave more offspring than others. (Birds with webbed feet may survive better and produce more offspring because they are more efficient at swimming and catching food than birds without webbed feet.) ● Survival and reproduction of the fittest→ individuals who best live to make babies (directed by environment requirement) ● Results in adaptation.
Does natural selection act on phenotypes or genotypes?
● Acts on phenotypes→ in direct contact with the environment
What is balancing selection? How does the dominance of alleles maintain genetic variation in a population?
● Balancing Selection is the superiority. ● Preserves variation by "hiding" recessive alleles ● Heterozygote→ only one allele determines the dominance ● Frequency-dependent→ two different phenotypic forms in a population o Existing variations, historical constraints, compromises, and environmental changes→ fit; good enough because you have to work with what you have.
What is the genetic definition of Evolution? Why is it more accurate?
● Biological or organic evolution: change in the biological properties in populations of organisms over the course of generations (change over time) ● Genetic: change in allele frequencies from one generation to the next in a biological population (not individual) o Change in frequencies of alleles in the gene pool
What are the two main causes of sorting among different alleles of genes that leads to evolution?
● Chance and natural selection (processes)
Be able to make connections between genotype frequencies and the evolution of phenotype through changing environmental requirements.
● Change in allele frequencies between generations in a biological population o Genes determine form of an organism (phenotype) and what is inherited (genotype into gametes) o Environment determines which phenotypes work the best→ survival and leaving more babies to the next generation (populations evolve) o Environments and requirements change over time ▪ Organism's phenotype follows what is required in the new environment→ population's evolve
Can we document that a population's traits are observed to change?
● Change in the ash content in the air= dark trunks ● Light→dark (sooty air) →light (clean air)
What affect does gene flow have on the genetic variation between populations?
● Decreases variability (makes the variation between the populations more similar)
Why do we know that evolution and natural selection are not goal oriented?
● Evolutionary trend does not imply that evolution is goal directed o We don't receive perfect traits
Which forces of evolution lead to a decline in genetic diversity in a population?
● Genetic drift and gene flow
Why can't natural selection produce a "perfect" phenotype?
● Good enough is "ok" because there are environmental changes and many traits have multiple functions. o Only possible to choose between traits that exist at the time.
Why was the voyage of the Beagle essential in shaping Darwin's thinking?
● He collected thousands of plants and animals as well as fossils. Darwin realized that natural forces gradually changed Earth's surface and that these forces are still operating in modern times. Darwin's experiences on his voyage led him to seriously doubt that earth and all its living organisms had been specially created only a few thousand years earlier. Darwin realized the earth was really old and constantly changing. ● The voyage allowed him to make observations o Similarity of forms on different continents o Diversity of environment (similar, but unique) o Ocean organisms were found at the tops of the Andes o Areas of high, unique species diversity o Unique island communities
What is the difference between natural and artificial selection?
● In artificial selection, humans choose the desirable traits and breed only orga ● nisms with those traits. ● In natural selection, the environment does the choosing: Individuals with traits best suited to the environment survive and reproduce most successfully, passing those adaptive traits to offspring
Are mutations a huge force in the evolution of most populations?
● It is the ultimate source of genetic variation
At what level of biological organization does natural selection occur?
● It occurs at the population and is seen with the individuals
Define microevolution, population, and population genetics.
● Microevolution: between generations, over short amounts of time o Changes in the gene pool of a population, or sorting of the variation from one generation to the next ● Sorting of the variations from one generation to the next o Proportion of population with a particular trait or allele shifts from one generation to the next
What is the ultimate source v. the primary source of genetic and phenotypic variation in asexual v. sexual reproducing organisms?
● Mutation: ultimate source of genetic variation ● Asexual: Mutation ● Sexual: fusion of gametes, unique independent assortment of alleles during meiosis, random fertilization, and crossing over between non-sister chromatids during synapse. ● Genetically variable as an individual→ unique ● Population: not all variation is heritable
What are sources of genetic variation?
● Mutations o Changes in DNA sequences o Source of new alleles o Rarely are advantageous ● Sexual reproduction o Crossing over- prophase 1 of meiosis o Metaphase I - orientation of homologous chromosomes (followed by separation in anaphase I) o Random fertilization ● Chromosomal duplication through errors in meiosis can provide an important source of genetic variation. If a repeated segment of DNA can persist over the generations, mutations in duplicated genes may accumulate, eventually leading to new genes with novel functions. ● Mutation: new alleles originate by mutation, a change in the nucleotide sequence of DNA. Mutation is the ultimate source for genetic variation that serves as raw material for evolution. In multicellular organisms, only mutations in cells that produce gametes can be passed to offspring and affect a population's genetic variability. ● Sexual Reproduction: in organisms that reproduce sexually, most of the genetic variation in a population results from the unique combination of alleles that each individual inherits.
How does natural selection lead to adaptation?
● Natural selection acts on phenotypes→ only genes get passed ● Natural selection is a blend of chance and sorting: chance in the random collection of genetic variation packaged into gametes and combined in offspring, and sorting in that some alleles are favored over others in a given environment. ● Because of this sorting effect, only natural selection continuously leads to adaptive evolution (evolution that results in a better fit between organisms and their environment.)
At what level of biological organization does evolution occur?
● Natural selection acts on the phenotypes of individuals→ seen in the organism ● Evolution is seen in population→ shifts average differences in a population's traits between generations
How does natural selection explain biodiversity?
● Natural selection leads to biodiversity ● The fossil record, which is the sequence in which fossils appear within layers of sedimentary rocks, provides some of the strongest evidence of evolution. The geographic distribution of species, known as biogeography, was the first thing that suggested to Darwin that organisms evolve from ancestral species. Anatomical similarities between species give signs of common descent. Similarity in characteristics that result from common ancestry is known as homology. ● Advances in molecular biology have enabled biologist to read a molecules' history of evolution in the DNA sequences of organisms.
Outline Darwin's logic of descent with modification through natural selection.
● Organisms produce lots of offspring. ● And yet, year after year, population levels (number of individuals) stay the same. ● Resources are limiting (Not enough resources for the entire population→ food, water, and shelter) o Conclusion 1: There is a struggle to survive more offspring are born than can be supported by the available resources. ● Individuals within populations vary in their physical traits. ● Some of that variation is heritable→ can be passed on to the offspring of the next generation o Conclusion 2: In the struggle for limited resources needed for existence, those variations that confer advantages are perpetuated and passed on to the next generation. The traits of the next generation are determined by which individuals survive and reproduce.
The probability of a gamete having a particular allele in a population is equal to what?
● P + q= 1
What is a mathematical model? What does HWE say about the change in allele frequencies between one generation and the next?
● P2+2pq+q2 ● Hardy- Weinberg principle is for a sexually-reproducing, diploid population • Alleles and genotype frequencies remain constant • UNLESS outside forces act to change the frequencies For a population to maintain genetic equilibrium (remain in Hardy-Weinberg equilibrium), five conditions must be true: 1. Very large population 2. No gene flow 3. No mutations 4. Random mating 5. No natural selection
What is genetic drift and how does it work?
● Random changes in allele frequencies ● Genetic drift→ (Chance): population is small o Bottleneck: not all alleles are represented in the new generation
Differentiate between assortative mating and sexual selection.
● Sexual Selection is non-random o Sexual selection is a form of natural selection, in which individuals with certain traits are more likely than other individuals to obtain mates. ● Assortative mating is random o Males tend to have the absurd morphologies ▪ Females make and nurture the babies
What are the three types of natural selection?
● Stabilizing Selection o Decrease variation, but the trait's average value does not shift. o Favors intermediate phenotypes. ● Directional selection o Shifts the overall makeup of the population by acting against individuals at one of the phenotypic extremes. o Average value moves and the variation either stays the same, or decreases a little. ● Disruptive selection o Typically occurs when environmental conditions vary in a way that favors individuals at both ends of a phenotypic range over individuals with intermediate phenotypes. o Variation increases, but the average value does not change.
Natural Selection can work at two different levels; what are they and how do they interact?
● Survival, or reproduction ● You have to survive to sexual maturity in order to get the chance to reproduce.
What is the importance of environmental context to natural selection?
● The environment can affect who survives
How is genetic variation maintained in populations?
● Through mutations (makes new varieties) and diploidy/sexual reproduction (processes of meiosis shuffle existing combinations of traits)
What four things must happen for natural selection to work in a population?
● Variation in traits ● Some traits heritable (not environment) ● Life is a struggle (more individuals are born than will survive to reproduce.) ● Some individuals with an advantage
Who was Alfred Wallace and what were his contributions to the study of evolution?
● Wallace wrote to Darwin and published jointly with him→ he pushed Darwin to publish it.