ANTH 4040

Structural genes

directly related to cellular activities and structure eg collagen, actin and myosin for muscle fibers, lysozymes, hemoglobin, fibrinopeptides

Systematics: Three systematic approaches

evolutionary systematics phenetic systematics phylogenetic systematics (cladistics)

Ultimate result of genetic drift is

fixation of an allele.

Evolutionary systematics

Birds Reptiles Crocodilians Lizards and snakes Turtles Mammals

Phylogenetic Systematics

Birds w/ Crocodilians Lizards and snakes w/ turtles Mammals alone

postzygote mechanisms

Hybrid zygote (embryo or fetus) does not survive; Hybrid survives but is sterile

Natural Selection

differential reproductive success among individuals in a population (or species).

Consensus among evolutionary theorists

1. biological species concept is the most useful 2. Speciation occurs in allopatry - difference of opinion as to whether "classic" or peripatric (including punctuated equilibrium) mode is predominant. 3. Sympatric speciation either does not occur or is infrequent

Critical issues with punctuated equilibrium

1. extinct species are diagnosed by morphological traits. We define fossil specimens to be of the same species if they share morphologies. Fossil specimens are assigned to different species based on morphological differences. Consequently, we implicitly impose some degree of morphological stasis on extinct species. 2. Is there no meaningful anagenesis? Is macroevolution fundamentally different from microevolution?

3 Tenets of theory of punctuated equilibrium:

1. speciation is raped - there is major genetic reorganization in a small population - mutation and genetic drift are the principal forces of evolution in speciation 2. all morphological differences between parent and offspring species arise at speciation event - morphological innovations occur simultaneously with origin of species- changes in morphology that occur at speciation are random with respect to ecological circumstances. 3. no meaningful anagensis subsequent to origin of species - that is, gene pool and morphology of new species are intransigent/resistant to intra-specific change Different from peripatric model

Example of discordance b/t speciation and morphological change

Sibling species demonstrate that speciation can occur without significant morphological change

Evolutionary Species

A lineage (i.e., ancestor-descendant sequence of populations) evolving separately from other lineages and having its own evolutionary role and tendencies; That is, a lineage that evolves separately from all other lineages and can be identified by having one or more distinctive traits;Evolutionary species may have two or more chronospecies (i.e., paleospecies) within it; Problem in identifying whether chronologically separate groups are chronospecies or separate species

Why are there different taxonomies?

A researcher "does" taxonomy only after having done a systematic analysis - only after having determined the "relationships" among taxa. Researchers differ in their: assessment of relationships, approach to systematics. different systematic approaches can lead to different taxonomic classifications

Geographical separation of populations within a species

Allopatry; Parapatry; Sympatry

Anagenesis

Also called phyletic evolution; Entire species evolves as a unit over time in response to change in selection pressures; Anagenesis is due to combined action of gene flow and directional selection; Use biological and evolutionary species concepts; Paleospecies are identified; Gaps in fossil record allow us to subdivide a continuously evolving lineage into paleospecies; No increase in number of species at any point in time

Mutation as a force of evolution

Although mutation rate is too low for mutation to be the principal force of evolution, mutation is the source of new genes in a species (see force of evolution table)

Limitations of Ecological species concept

Assumes meaningful gaps or discontinuities in niches to which species can adapt How to delimit a species that include populations that are geographically widespread and adapted to somewhat different niches

Multiple definitions of the term "species":

Biological species, Evolutionary species, Morphological species, Ecological species, Recognition species

Tempo of speciation

Comparing different modes of speciation in their relative time to speciation; Vicariant speciation takes the longest time; Stasipartic speciation takes the least time; based on the intensity of natural selection

Issues about accuracy of Molecular Clock Model

Computation of mutation rate: Problem - estimates of dates of evolutionary divergence based on fossil record are always the minima because of the low likelihood that we find fossils that demonstrated the absolutely earliest evidence of lineage divergence.

Limitations of biological species concept

Different species can interbreed with one another, sometimes producing sterile but other times producing fertile offspring; Concept does not apply to asexual species; How to identify reproductive (in)compatibility in extinct species?

Prezygote mechanisms

Different species occupy different habitats, even though the species may be sympatric; Mate at different times; Different mating behaviors; Mechanical problems with copulation; Vagina/uterus of one species does not permit sperm from another species to survive

Evolutionary Systematics:

ES expresses both evolutionary relationships and evolutionary history in taxonomic classification. ES bases taxonomic classifications on the twofold aspects of evolutionary processes: speciation and adaptation. That is, evolutionary history consists of emergence of new species (cladogenesis) and subsequent divergence of a species from its ancestor (anagenesis). ES expresses both phylogenetic relationships and grade of adaptation in taxonomy Grade - group of organisms with same level of structural organization, including biology and behavior. ES considers all traits in systematic analysis. Some traits are considered to be more important than others in illustrating adaptive divergence. These important traits are assigned differential "weight" in analysis. Taxonomic classification seems to be subjective; individual researchers decide which traits are most important in illustrating adaptive divergence. Therefore, taxonomy seems subjective and arbitrary, and may not be repeatable.

Limitations of recognition species concept

Epigamic traits are those that attract members of the opposite sex. How do we identify epigamic traits? Are all sexually dimorphic traits epigamic, and how do we identify epigamic traits in extinct species? Biological species concept is the most commonly used Conjoin Biological and Evolutionary species concepts - for extinct species, identify distinctive suite of traits for a lineage; assume that possession of these traits is due to shared gene pool

Speciation and morphological change:

Evolution is change in genetic structure of a species; Genes code for protein; Proteins make up morphology; Therefore, change in genetic structure of a species should correspond with change in morphology; Alternatively stated, magnitude of morphological change should correspond to magnitude of genetic change; Analyzed 44 proteins in humans and chimpanzees; Compared human-chip differences with those of sibling species; Postulated that there is a hierarchy in the genome: regulator genes and structural genes

Interpretation of fossil record

Extinct species are "morphological" species, albeit interpreted within biological species concept; That is, a paleontologist must decide whether individuals with different morphologies would have been members of the same gene pool.

Gene duplication

For a particular gene, there may be selection against its mutation. With gene duplication, one of the duplicate genes can mutate and may not be selected against because the other gene produces the necessary protein. The mutated gene may become an (dis)advantageous or neutral variant, or dysfunctional (pseudogene). The suite of related genes is a gene family. Gene duplicated may be an important process for creating genetic variation

Structure of a genome: gene family

Gene family - series of genes (often contiguous on a chromosome) with related function. Gene family arises by gene duplication (due to unequal recombination).

Structure of a Genome

Gene is subdivided into exons and introns. Exon - part of the gene that is translated into a protein. Intron - part of the gene that is not translated into a protein. Only exons are expressed phenotypically in protein and, therefore, subject to natural selection.

Unit of natural selection

Gene; Individual organism; classic Darwinian theory; Group (i.e., population); species

Mutation Rate

Gross generalization: mutation rate per gene per generation is 10^-5 or 10^-6 (i.e., 1/100,000 to 1/1,000,000); 25,000 - estimated number of protein coding genes in humans; Mutation rate (0.025 to 0.25) is too low to be the principal force in evolution; Between 5% and 44% of us carry a genetic mutation compared to our parents

Morphological Species (phenetic)

Group of organisms that shares a suite of traits and looks different from other groups of organisms;This is a typological concept - subjective; except differences among researchers in defining "types"

Biological Species

Group(s) of actually or potentially interbreeding organisms that are reproductively isolated from other such groups. A species is a "bounded" gene pool; members of the same species are part of the same gene pool; members share genes. A biological species is the unit of evolution. Reproductive isolation protects a species (i.e., its gene pool) from hybridization with another species; Natural selection leads to adaptations in a species to an ecological niche. The bounded gene pool prevents unwanted incursion of genes/allele from other species not adapted to the same niche. Although hybridization with another species would increase genetic variability, hybridization would also disrupt adaptations.

Explanation of genetic polymorphism: Natural Selection

Heterozygotes have natural selective advantage over homozygotes (called balanced polymorphism). Diversity of selection pressures such that different alleles have selective advantage

Explanations for intraspecific genetic variation: natural selection and genetic drift

Intraspecific genetic variation: polymorphism Polymorphism - situation in a population of having ≥ 2 alleles Of a gene, with the alleles having a frequency ≥ 1% Approximately 28% of human genome is polymorphic

Systematics and Taxonomy:

Kingdom (Animalia)-->Phylum (Chordata)-->Subphylum (Vertebrata)-->Class (Mammalia)-->Order (Camivora)-->Family (Canidae)--> Genus (Canis)-->Species (C. lupus)

Interpretation of fossil record

Marked morphological differences between species need not imply quantitatively marked genomic difference. Is morphological change "abrupt"; involving regulator genes; is speciation "rapid", occurring in peripatry? Theory of speciation by peripatry involving regulator genes does not nullify importance of coordinated evolution of structural genes.

Interpretation of fossil record

May underestimate or overestimate the number of species in a lineage; Speciation can occur without marked morphological change (sibling species); marked morphological change can occur without speciation (punctuated anagenesis)

Systematics and Taxonomy:

Modern biologists use taxonomy to communicate ideas about evolutionary relationships Pan paniscus, Pan troglodytes, Gorilla gorilla > explain or communicate relationships between these You can infer that two species categorized in the same genus are believed to be more closely related evolutionarily to each other than they are to species in another genus

Molecular Clock Model

Molecular clock model - estimates date of speciation between two living species. That is, when did two species last share a common ancestor. Neutral mutation theory is the foundation of molecular clock model. Assumptions of molecular clock model: Predominance pf mutations are neutral. For any two species, linear relationships between time since their lineage divergence and number of mutation between them. For a particular gene, mutation rate is constant among species.

Explanation of genetic polymorphism: Genetic Drift

Most mutations are "neutral" with respect to natural selection, and these mutations increase to polymorphic levels due to genetic drift Theory of neutral mutation

Molecular Clock Model

Mutation rate is calculated by ascertaining the number of nucleotide differences between two living species, and dividing the difference by the length of time since their evolutionary divergence. Time of evolutionary divergence is determined by fossil evidence. Once mutation rate is calculated, then apply it in reverse. That is, determine date of evolutionary divergence of another pair of species using calculated mutation rate and number of nucleotide differences between those species. Apply in reverse for another pair of species: number of years since evolutionary divergence = # nucleotide differences between two living species/mutation rate.

Issues about accuracy of molecular lock model

Natural selection and generation length may upset calibration of the clock. Genes evolve at a different rates, which implies natural selection. Which aspects of the genome would be best for using molecular clock model: exons, introns, or pseudogenes? For a particular gene, length of time o fixation of a mutation should be proportional to generation length. Species with shorter generation lengths should accumulate more mutations than species with longer generation lengths.

Theory of neutral mutation

Neutral (silent) mutation - mutation that does not change the natural selective advantage of the phenotype Reasons that a mutation can be "neutral": Redundancy of genetic code - 64 codons for 20 amino acids Mutation alter the protein, but the change occurs in a part of the protein that does not meaningfully affect the phenotype Mutation occurs in an intron or pseudogene

Principle of Competitive Exclusion leads to character displacement

No two species can occupy the same niche. There will be one of three outcomes: (1) one species goes extinct; (2) one species emigrates; or (3) the species undergo character displacement to reduce their direct competition

Cladogenesis

One species splits into two species; At a point in time, there is an increase in the number of species; Different modes are based on: (1) extent of geographical separation of populations within a species, and (2) different mechanisms of evolution that are principal in producing speciation; "classic" allopatric speciation. As natural selection leads to adaptation within a species the speciation process can be considered to be adaptive. At speciation the new species is already adapted to its environmental circumstances, and the reproductive isolation that accompanies speciation serves to protect the new species gene pool from hybridization with the parental species as well as other species

Two limitations in making phylogenetic statements using taxonomy

Phylogeny - evolutionary lines of descent; ancestor-descendant relationships Two limitations: cannot express chronology cannot express exact ancestor-descendant relationships

Comparative evolutionary biology of polymorphism: Natural Selection

Polymorphism is a more stable phenomenon. Stability of polymorphism is based on stability of natural selective pressure. Change in selective pressures will lead to change in allelic frequencies

Comparative evolutionary biology of polymorphism: Genetic Shift

Polymorphism is a more transient phenomenon. The multiple alleles of a gene randomly fluctuate in their frequencies until one allele becomes "fixed". Subsequent to fixation, a new neutral mutation may occur. By genetic drift, the new mutation increases in frequency, and the "fixed" gene now becomes polymorphic. The genome is in flux; genes that are currently fixed will become polymorphic, and genes that are currently polymorphic will become fixed.

Polymorphism due to genetic drift

Polymorphism occurs by genetic drift acting on neutral mutations o That is, by chance some mutations will increase in frequency to polymorphic levels

Gradualism

Population of a species are large and initially genetically homogeneous due to gene flow; The population diverge from one another genetically principally by natural selection. The populations become geographically isolated from one another, gene flow is blocked; If the gene pool differences preclude interbreeding between the two populations then speciation has occurred

Sympatry

Populations have broad geographical overlaps; share the same geographical area "classic" sympatry Principal force of evolution: (diversifying) natural selection Stasipatry

Parapatric speciation

Principal force of evolution - natural selection; Populations have narrow range of geographical overlaps; sharp ecological gradient between contiguous populations

Statsipatric speciation

Principal force of evolution; Gross chromosomal mutation; Possible explanation for hominoid evolution; Punctuated equilibrium: different mode of speciation, or just peripatric speciation

Phylogenetic Systematics (Cladistics):

Problems distinguishing between traits that are homologies vs. homoplasies a synapomorph must be an homology (trait must not be a homoplasy and misclassified as synapomoprh) This distinction is important for ES as well; not relevant for phonetics Definitions: Homology - similarity in form between two species due to common ancestry Homologous traits are indicative of common ancestry Homoplasy - similarity in form between two species due to common adaptation (i.e., convergent or parallel evolution) and not due to common ancestry. The similar structures evolved independently.

Structure of a genome: pseudogene

Pseudogene - sequence of nucleotides that is similar to the sequence of nucleotides in a functional gene, but the pseudogene is not translated into a functional protein. The pseudogene is rendered inactive by one or more mutations

Speciation and Hierarchy in genome

Regualtor and structural genes imply co-adapted gene complexes (speciation involving peripatry or punctuated equilibrium?)

Interpretation of fossil record

Researcher's theoretical position influences interpretation of evolutionary history species' identification: biological, evolutionary, morphological, ecological, recognition mode of speciation: saltational or gradual Despite theoretical differences among researchers, we can interpret adaptive change within a lineage over time. Change in morphology that persists over a long period of time represents adaptation, which is due to natural selection

Problems with phylogenetic systematics

Selection of correct genealogy Cladists create a branching diagram of paired associations among species based on the number of shared derived traits (i.e., synapomorphs). There may be inconsistencies in the analysis due to unidentified homoplasy. Cladists select the cladogram with the fewest inconsistencies. Creation of biological puzzling taxonomic classifications

Peripatric speciation

Small population's gene pool influenced by mutation, genetic drift, and inbreeding; Genome consists of regulatory genes and integrated gene complexes; heterozygosity is disadvantageous

Gene's code for proteins

Step one - transcription: formation of MRNA Step two - translation: formation of protein Sequence of nucleotides in a gene determines sequence of amino acids in a protein

Comparison of systematic methods

Systematic approach: goals and traits used. Evolutionary systematics: geneaology and adaptive divergence all traits; differential importance of some traits. Phenetic systematics: overall similarity all traits; each trait is equally important. Phylogenetic systematics: genealogy shared derived traits.

Which taxonomy is correct?

Taxonomic classification depends on a researcher's goal

Molecular Evolution

Theory of molecular evolution and fossil record Issues to discuss: genetic variation within a species - natural selection vs. neutral mutation and genetic drift molecular clock model to estimate date of speciation event

What is a Codon?

Triplet sequence of nucleotides, in DNA or messenger RNA (mRNA), that specifies a particular amino acid · Protein is made up of amino acids

Natural Selection

differences among individuals in reproductive success

Allele

a genetic marker i.e. blood types (A, B AB, O)

Ecological species

a group of organisms exploiting (or adapted to) a single niche

Peripatric speciation tempo

adaptive landscape is of rough topography a species gene pool occupies a summit of a hill genome consists of integrated complexes of genes in speciation, emergent species may pass from one summit to another summit. To do so, species must pass through a valley of lowered adaptation. Valley must be transgressed quickly or the emergent species will go extinct. Therefore, genomic change in speciation must be done quickly.

Inclusive Fitness

an individual's genetics contribution to the next generation is based on both one's own reproduction and the reproduction of one's relatives; My genetic representation in the next generation is the same whether I have 1 child, my sibling has 2 children, or my first cousin has 8 children.

Mode of speciation

anagenesis and cladogenesis

Sibling species

are different species that are virtually morphologically identical.

Substitution Point Mutation

can be synonymous (neutral or silent) or non-synonymous (meaningful)

Taxonomic Categories:

categories above "species" are arbitrary constructs to enable researchers to make "sense" out of diversity of species. Researchers can include as many categories as necessary to make explicit phylogenetic relationships

Microevolution

change in allele (genetic structure) frequencies of species overtime

Point Mutation

change in one nucleotide;Resulting protein is so altered that it is typically functionless

Macroevolution

change which results in origin of new species; change in allele frequencies overtime

Non-synonymous (meaningful) point mutation

codon that results from mutation specifies a different amino acid from the codon prior to mutation; result is a change in the protein that is produced.

Synonymous (neutral, silent) point mutation

codon that results from mutation specifies the same amino acid as the codon prior to mutation; result is no change in the protein that is produced

Regulator genes

control timing and rate of activity of structural genes ex. Hox genes: are regulator genes; Hox genes modulate activities of suite of structural genes One regulator gene may modulate activity of a group of structural genes. Change in a regulator gene may profoundly affect growth and development.

Mutations affecting larger sections of a chromosome

deletions, duplication, inversion, insertion, and translocation; gene position may or may not be important in its expression; mutation can affect number of chromosomes (trisomy 21 - down syndrome)

Utility of Molecular Clock Model

despite limitations of Molecular clock, its results are generally concordant with paleontological and comparative anatomical evidence in terms of nearness of phylogenetic relationships. If molecular clock and paleontological evidence are in disagreement, then prompts both sets of researchers to reevaluate their interpretations.

Phenetic Systematics:

developed to be a more "objective" method than ES in doing taxonomic classification. Pheneticists consider as many traits as possible in systematic analysis, and assign equal weight/significance to each trait Multivariate statistical analysis identifies organisms that share clusters of traits. Assignment of organisms to a taxon is based on overall similarity. Pheneticist regards morphological similarity as being informative of genealogical relationships Problem - may unintentionally differentially weight traits traits are part of integrated, morphological complexes; an organism cannot be dissociated into a series of independent traits. Phenetics is not objective and repeatable as it was designed. Could get different taxonomic classification depending on traits selected for analysis

Systematics and Taxonomy:

formal way to write species' name - Genus species or Genus species Taxonomic classification creates a suprastructure of order on biological diversity Only the "specie" category is a true biological unit; a species is the evolving unit Higher taxonomic categories (genus - kingdom) are not real biological units. They are our imposition of order on the diversity of species.

Fixation

frequency of one allele is 1.0, and all other alleles of the gene have been eliminated from the population

Theory of punctuated Equilibrium

gaps in fossil record present data about tempo of speciation

Theory of gradualism

gaps in fossil record represent imperfections/vagaries in fossilization process

1 force inhibits speciation

gene flow

Structure of Genome

gene is a segment of chromosome genes codes for production of protein protein is a sequence of amino acids protein is functional in the body; polypeptide is: chain of amino acids. genetic code is redundant: 64 codons and 20 amino acids codon - triplet sequence of nucleotides in DNA

Peripatric Speciation

geographical isolation of small population; small population has less genetic variability than the large pop (founder effect); principal forces of evolution in speciation - mutation and genetic drift; inbreeding in the small population, although not a force of evolution, promotes; speciation by increasing homozygosity

Could lineage divergence between humans and great apes be due to stasipatric speciation?

great apes have 48 chromosomes, whereas humans have 46 chromosomes reduction of chromosome number due to fusion of 2 chromosome in hominoid ancestor

Stasipatric speciation: another type of sympatric speciation:

gross chromosomal mutation occurs, which is not necessarily adaptive; heterozygous for gross chromosomal mutation has lower fitness than a homozygote (for either non-mutated chromosome or mutated chromosome) that is, selection against heterozygotes; inbreeding leads to homozygosity for mutation; speciation is fast; principal force of evolution - mutation

Recognition Species

group that shares a common method of recognizing mates and shares a common fertilization system

Evolutionary species concept

has a diachronic (i.e., across time) perspective, whereas biological species concept has a synchronic (at one time) perspective.

Heterochrony

heterochrony is change in growth pattern, involving rate, onset, and duration. Perhaps due to regulator gene involvement.

Unit of natural selection

individual organism

Frameshift point mutation

insertion or deletion of a nucleotide, which changes the "reading frame" for codons

Kin selection

just more natural selection at level of individual organism; individual may reduce her/his reproductive success by aiding the reproductive success of her/his "kin" (e.g., altruism); Kin selection is simply part of an organism's inclusive fitness and can be considered to be natural selection among individual organisms.

Gene Flow

movement of alleles from one population to another due to matings between populations; Gene flow can introduce new alleles into a population or change frequency of existing alleles.

sequence of processes leading to speciation

mutation occurs in regulator gene heterozygosity for regulator gene is disadvantageous; homozygosity is more favorable homozygosity can be achieved quickly by genetic drift and inbreeding many small, founder populations go extinct because they occupy a marginal habitat fate of species that arise by peripatric speciation due to major genetic change many species go extinct because the change was selectively disadvantageous some species are successful because the change was selectively advantageous populations have narrow range of geographical overlap; sharp ecological gradient between contiguous populations ecological gradient restricts gene flow between populations hybrids between the two populations have lower fitness compared to individuals whose parents are both members of one population or the other each population adapts by natural selection to its environmental conditions speciation occurs if diversifying effect of natural selection on the two populations gene pools is greater than the homogenizing effect of gene flow principal force of evolution - natural selection

Four forces of mutation

mutation, gene flow , genetic drift, natural selection

3 forces of evolution that promote speciation

mutation, genetic drift, natural selection

Adaptation occurs

only if differences among individuals in reproductive success have some inheritable basis.

Fundamental Theorem of Natural Selection

opportunity for natural selection is directly related to genetic variability in a population (or species); There must be genetic differences among individuals in a population (or species), and correspondingly phenotypic differences, for there to be natural selection; Natural selection "acts" directly on phenotypic variability, and indirectly on genetic variability.

Genome is integrated

organism's genome is integrated. that is genome consists of hierarchy of gene complexes - genes interact with one another, and genes are under the control of other genes mutation in "higher level" genes (regulator genes) has multiplicative effect; natural selection acts on gene complexes rather than on individual genes

unit of evolution

population or species

Mechanisms that serve to maintain reproductive isolation of a species by blocking hybridization

prezygote and postzygote mechanisms

Genetic Drift

random change in allele frequencies; estimate of magnitude of evolution by genetic drift = (pXq/N)^0.5 where "p" and "q" are frequencies for 2 alleles of a gene, and "N" is population size. Two inferences from formula: 1. All populations evolve every generation by genetic drift. 2. Magnitude of evolution by genetic drift is greater in a smaller population than a larger population.

Bottleneck and Founder Effects

reduction in genetic variability by chance due to reduction in population size (bottleneck) or establishment of a new, founder population.

Adaptation

result of natural selection; Individuals are subject to natural selection, whereas populations (or species) adapt.

Gene

segment of DNA that codes protein

Stabilizing Selection

selection against individuals at both ends of the phenotypic distribution curve; Result is to reduce variability in the distribution curve, but no change in the mean value.

Diversifying Selection

selection against individuals in the intermediate range of the phenotypic distribution curve, and selection for individuals at the ends of the distribution curve. Result in two modalities in phenotypic distribution

Directional Selection

selection for individuals at one end of the phenotypic distribution curve; Result is a change in the mean value of the distribution

Mutation

source of new genes for a species; random change in genetic material; different levels of scale from one; nucleotide to the number of chromosomes; mutations can happen in somatic and sex cells

Punctuated Equilibrium: another mode of speciation or just peripatric speciation

speciation is rapid; a lineage's evolutionary history is characterized by brief pulses of speciation, followed by long periods of species' stasis (no anagentic change)

alternative argument for evolution of cichlid fishes

speciation occurred when populations were in allopatry, and species have now become sympatric current lake was subdivided into several lakes in the past. speciation occurred during this period of allopatry lakes than coalesced into the single lake of today

Character Displacement

species living in the same area and exploiting the same resources will undergo selection for traits that lowers their competition

Three "types" of natural selection

stabilizing selection, directional selection, and diversifying selection

Hierarchy in Genome

structural and regulator genes

Chronospecies

successively named species within a single evolving lineage; identified by significant morphological change in the lineage over time. Gaps in the fossil record provide the opportunity to name successive species

Systematics and Taxonomy:

systematics - study of diversity of organisms and relationships among them. Taxonomy - system for classifying organisms. use taxonomic scheme devised by Carolus Linnaeus. Category - rank in taxonomic classification. Taxon - group of real organisms that are classified together in a category.

Phylogenetic Systematics (Cladistics):

taxonomic classification is based exclusively on genealogy. Cladists evaluate all traits in a comparison of organisms. However, they partition traits into ancestral (plesiomorphic) and derived (apomorphic) traits. Definitions: Ancestral trait - not a recently evolved trait; trait that is possessed by a number of species within a lineage. Derived trait - trait that has been transformed from an ancestral trait. Symplesiomorph - ancestral trait shared by two or more species Synapomorph - derived trait shared by two or more species Autapomorph - trait that is unique to a species Cladists use only synapomorphs in systematic analysis species that share a derived trait by inference have a common ancestor in whom that trait first appeared

Classic sympatric speciation

theoretically difficult to accept; issue: how is gene flow blocked to allow speciation when two populations share the same geographical area? sympatric speciation may occur in a situation of ecological mosaicism; mosaicism promotes behavioral specialization; diversifying selection due to behavior specialization results in discrete populations; reason is that hybrid individuals between the sympatric populations have low fitness in both ecological contexts

Codon

triplet sequence of nucleotides that specifies a particular amino acid (24 amino acids and 64 codons)