Unit 3 Learning Goals - IB 150

Differentiate between different sources of diversity among individuals in a population, including heritable variation and environmentally-induced variation due to phenotypic plasticity.

∙ heritable variation: based on organism's genes

∙heritability: proportion of observed differences in a trait among individuals of a population due to genetic differences

∙environmentally-induced variation: variation that results from environmental influences

Identify variation that is of evolutionary significance

∙ Evolution only applies to heritable variation in traits, and specifically to changes in allele frequency of different alleles of a given gene associated with such a heritable trait over time or between generations

∙Variation provides options for natural selection to "choose" what is best for the population as a whole. This is why genetic variation is important to natural selection.

Define biological evolution with respect to allele frequencies

∙When we talk about evolution in biology, (specifically microevolution), we are talking about changes in the frequency (abundance) of different alleles of a gene in a population over time. Note: this means that not everything that changes in a population over time hence falls under this definition of biological evolution

∙ Group of same species and live in same geographic area and at the same time and regularity interbreed

∙Evolution is defined as any change in the frequency of alleles within a gene pool of a population from one generation to the next

Calculate allele frequencies given genotype frequencies or number of individuals with each genotype

∙ Allele frequency calculation: p + q = 1

∙ p=frequency of dominant allele

∙ q=frequency of recessive allele

Explain (in your own words) the predictions of the Hardy-Weinberg (HW) Principle.

∙ This predicts how gene frequencies will be transmitted from generation to generation given a specific set of assumptions; if an infinitely large, random mating population is free from outside evolutionary forces, then the gene frequencies will not change over time and the frequencies in the next generation will be p² for the AA genotype, 2pq for the Aa genotype and q² for the aa genotype. In other words, a population is not evolving if in HW equilibrium.

∙ p² + 2pq + q² = 1

→p²= homozygous dominant allele frequency

→ q²= homozygous recessive allele frequency

List and restate (in your own words) the five assumptions/conditions of the Hardy-Weinberg principle, and know under which conditions it is OK to make these assumptions, or why you are testing for violations of these assumptions.

∙ five conditions for HW Principle:

1. no mutation

2. random mating

3. no gene flow

4. infinite population size

5. no natural selection

∙ These violations of HW equilibrium represent evolutionary forces:

- Mutations → violate HW equ. by the addition of alleles to population

- Genetic drift → violate HW equ. due to sampling error leading to random fluctuations of allele frequencies

- Gene flow → violate HW equ. by the addition of alleles to population

- Natural selection → violate the HW equ. assumption that all individuals are equally likely to reproduce and produce same number of offspring

-Non-random mating (is a violation of HW , but doesn't change allele frequencies) → violates HW assumption of random mating

∙ Conditions and Violations of the HW Principle:

→ Any population will be in HW Equilibrium with respect to their genotype frequencies, IF:

- Every individual produces gamete genotype in the same proportions as alleles represented by their genotype

- Every individual is likely to pass on their alleles to the next generation (everyone leaves the same number of offspring)

- Every individual is equally likely to reproduce with any other individual in the population, regardless of genotype (random mating)

- There is no other external factor altering allele or genotype frequencies

Predict allele and genotype frequencies of rare genetic disorders in a population from phenotypic data alone, ASSUMING that the population is in Hardy-Weinberg Equilibrium, and understand the limitations of your estimates.

Calculate the expected frequencies of offspring of particular genotypes or phenotypes expected in the next generation if the population is in Hardy-Weinberg equilibrium given allele or genotype frequencies in the current generation

Be able to apply the Hardy-Weinberg equation to estimate the frequencies of carriers in a population, assuming alleles of the gene in question is in Hardy-Weinberg Equilibrium

Understand in what sense the Hardy-Weinberg equation represents the prediction of the null hypothesis of biological evolution.

∙ The null hypothesis that is being tested is whether the observed and expected values are not significantly different from one another

∙ Reject null hypothesis if chi square test results are p<0.05

∙HW equation provides a null hypothesis for evolutionary change

Determine whether or not a population is in Hardy-Weinberg equilibrium using the Chi-Square statistic to compare expected and observed genotype frequencies of a population, and explain the biological implications of either rejecting or failing to reject the null hypothesis based on your results.

List the four processes that change allele frequencies and the five that change genotype frequencies in populations through time.

∙ Four processes that change allele frequencies: mutations, selection, genetic drift, gene flow

∙ Five that change genotype frequencies in populations through time: mutation, genetic drift, gene flow, natural selection, assortative (non-random) mating

∙ Process that does not alter allele frequency: assortative mating

Restate (in your own words) what it means for an allele to be fixed in a population or lost from a population.

∙ Before an event, there are at least two variants of an allele. After an event, such as genetic drift, only one of those variants remain as they had been favored.

∙ Fixation is when an alleles frequency in a population reaches 100%. This would result in no more variability in the population for this gene. Individuals would always be producing offspring carrying only that allele.

Relate allele fixation to genetic diversity (e.g., what is the effect of fixation on genetic diversity?).

∙ There would be no genetic diversity

∙ When an allele becomes fixed, genetic diversity decreases since only one of the many variants remains at the end.

Identify processes that can cause alleles to be fixed or lost and re-introduced.

∙ genetic drift

→ Drift contributes more to changes in allele frequencies, the smaller the population is

→ Allele frequencies shift randomly and sometimes may disappear/reappear in populations, so variations of a certain allele may disappear completely, leaving at most one variant in the population. The loss of alleles can always come back →Genetic drift is due to chance.

Describe the concept of "random sampling of alleles" in genetic drift making specific reference to the parental gene pool and offspring genotypes.

∙ Small samples are often different from the wider populations, and differences in small populations don't get "averaged out" as compared to differences in large populations from generation to generation. Random pairings from the parental gene pool meant that for a small selection, there is a higher chance that the offspring phenotype will be skewed from those of the overall population

∙ When two individuals of particular genotypes mate and produce offspring, which alleles the offspring inherit are simply due to chance, thus being a process of "random sampling of alleles" since that random chance determines the next generation's gene pool

Understand how genetic drift can cause alleles to become more or less common or fixed in populations

∙An allele becoming fixed by genetic drift alone is most likely in a very small population.

∙ Strong genetic drift in very small populations can increase the chances of fixing a random allele even if the allele is deleterious

∙ Individuals with a certain allele leave the population then they become less common and possibly making a different allele that was left behind in the population makes the that allele more common and possibly fixed

∙Individuals with a certain allele leave/enter a population take/bring certain alleles with them, changing allele frequencies. That said, they can become more or less common, depending on how great of an impact genetic drift has on a population (whether it be small/large population size or how many individuals are migrating). With the help of genetic drift, allele fixation may occur as well because variants may leave/enter.

Predict the relative effects of genetic drift in large vs. small populations and predict the relative time to allele fixation for large vs. small populations undergoing drift.

∙ Small populations = larger probability of error

→ Do not capture all the alleles; larger chance of creating different allele frequencies from one generation to the next

∙ Drift would not contribute as much to changes in allele frequencies in large populations

∙Genetic drift is a negligible evolutionary force in large populations

Compare and contrast the causes and consequences of the "founder effect" and population bottlenecks.

∙Founder effect

→ New territory is colonized by a group of individuals

→ Population starts from few individuals arriving in a new place

→ Ex: island that was never previously occupied by a new species

→ Single founder event

→ Repeated founder effect due to a migration front

→Can cause a fixation of alleles in population

∙Bottleneck events

→ Population size shrunk down to small number

→ Event that happens to crash population size and whoever survives it was because of chance, the survivor alleles are overrepresented

→May lose alleles after event

→ Human bottleneck event

- Toba volcanic explosion

→ Likelihood of passing on alleles due to chance is lower

→ Genetic footprints

Define gene flow and relate it to migration between populations

∙ Migration of individuals between populations

∙ Even low amount of gene flow can help allele diversity

∙Increases genetic diversity

∙ The movement of alleles between populations; occurs when individuals leave one population, join another, and breed

Explain how gene flow influences effective population size, allele frequencies, and genetic divergence between populations living in different regions.

∙ Gene flow determines the gene pool (the stock of different genes in an interbreeding population) that the others can act upon (genetic drift, mutation, and natural selection)

∙Gene flow can also reintroduce an allele

∙Gene flow can introduce new alleles to a population

∙Effective Population Size: The number of individuals in a population that contribute offspring to the next generation. When gene flow is present, more individuals with new alleles become part of that effective population size, contributing their own alleles to the offspring

∙In order for genetic divergence to occur, where a population speciates (separates into distinct species), gene flow must be absent. To diverge, populations must be isolated from one another, evolve independently, and then become reproductively isolated to be truly diverged

Understand how non-random mating can influence genotype frequencies, and be able to illustrate graphically why non-random mating alone will not change allele frequencies

∙ Assortative mating does not necessarily lead to a change in allele frequency because alleles are still passed on in the same proportion as they occur in genotype frequencies

∙ non-random mating (inbreeding and outbreeding), meaning the organisms look for specific traits in another organism to mate with, causing certain genotypes or allele frequencies to increase or decrease because there is an interest in them

∙Non-random mating (positive and negative assortative mating) changes genotype frequencies because homozygotes become much more common than heterozygotes. But, because heterozygotes still contribute to allele frequencies, allele frequencies do not change due to non-random mating

Predict how inbreeding will change genotype frequencies, and be able to graphically illustrate why non-random mating will not by itself change allele frequencies.

∙Reproduction with closer relatives often leads to a phenomenon called inbreeding depression, a reduction in fitness among offspring due to increased phenotypic expression of deleterious, recessive alleles

∙Inbreeding depression results in a decline in average fitness

∙Will increase amount of homozygous recessive individuals and work to increase frequency of the recessive allele

∙Always moving towards fixation for that allele

∙INCREASES genotypic frequency of homozygous recessive individuals in the population

∙natural selection then acts on the recessive phenotype and allele

∙while non-random mating on its own does not lead to changes in allele frequencies, it can indirectly act to enhance selection

∙Inbreeding, in a way, is non-random mating. The difference between the two is that inbreeding will most likely change genotype frequencies because, for example, if individuals of a family are predisposed to be carriers of a certain gene, and members of those families breed with each other, they are likely to contribute affected offspring. The affected offspring change genotypic frequencies in a population because then homozygous recessive individuals become more and more common as individuals continue to inbreed

Justify why inbreeding does not cause evolution directly, yet can speed the rate of evolutionary change.

∙Inbreeding only affects the genotypes of individuals in the population

∙Increases homozygosity by taking alleles from homozygotes and using them to create homozygotes

∙Inbreeding exposes deleterious recessive alleles to selection. After many, many generations of inbreeding, deleterious recessive alleles can be lost from the population. Once this occurs, a self-fertilizing population will not exhibit reduced fitness under additional generations of inbreeding.

∙Inbreeding can cause the expression of deleterious alleles, leading to very affected individuals. This greatly lowers the fitness of the individual and its ability to survive. But, inbreeding does not directly cause evolution because only a proportion of inbreds are affected and selected against. It is in the long run that we see evolutionary change. More inbreeding leads to more affected individuals, leading to natural selection selecting against the affected phenotypes, lowering those deleterious allele frequencies.

Justify why ALL natural populations will evolve, making reference to assumptions made under the Hardy-Weinberg Principle.

1. Some populations are large, some are small. Hardy-Weinberg assumes that an interbreeding population is indefinite because it is not evolving. But, even evolution occurs in large breeding populations because...

2. assortative mating is much more likely than random mating. Individuals usually choose their mates, not just spontaneously breed (ex. female choice and male-male competition)

3. Changes in allele frequency is inevitable. Genetic drift is the result of random changes in allele frequency.

Mutations are random and spontaneous that cannot be prevented

4. It is possible to isolate a population, which then leads to speciation, but, sometimes, that is not the case

5. Environmental pressures WILL favor certain genotypes over the other.

∙Remember the 5 conditions required to be in HW Equilibrium: large breeding population, random mating, no mutation, no immigration, no natural selection

List the four postulates of natural selection

1. pre-existing phenotype variation in the population

2. variation is heritable (has a genetic basis)

3. differences in reproductive success among individuals

4. reproductive success depends on this phenotypic trait

Discuss the consequences of differential survival and reproduction for variation in a population. (Why is "Survival of the fittest" not capturing the whole story?)

∙You have to be able to survive to produce offspring

∙You have to be able to acquire a mate and mate with that organism

∙Fitness

∙The reproductive success of an individual with respect to other individuals in the same population

∙While it is beneficial to be strong, fast, and healthy in order to survive for the longest amount of time, what really matters is one's ability to reproduce. A person with more offspring will have a higher fitness than that of someone with no offspring.

Compare and relate the roles of reproduction and survival in natural selection.

∙ Natural selection is the process by which traits that confer higher reproductive success in a particular environmental setting become more common in the next generation

∙If an offspring receives a trait that is environmentally favorable, they are more likely to survive and reproduce in that same environment than an organism who did not receive said trait.

Identify sexual selection as a sub-category of natural selection that increases reproductive success through mate acquisition.

∙Sexually selected traits can include mating displays in the context of "female choice" or "male - male competition"

∙Traits that may lower survival rate, but increases the chances of attracting a mate, can be evolved by natural selection

Define fitness in the context of natural selection.

∙ reproductive success: how many offspring an individual produces over their lifetime

∙ the ability of an individual to produce viable offspring relative to others of the same species

Identify that evolution by natural selection results directly from intraspecific competition between individuals of different genotypes.

∙results from competition among individuals of the SAME species with each other

∙natural selection operates via intraspecific competition

→ the changes in allele frequency in a population due to natural selection are always due to intraspecific competition between members of the same species that differ in genotype

Explain why natural selection does not result in evolution of a trait because a population "needed it", but can only operate on pre-existing variation in the population.

∙Natural selection a non-thinking process that individuals are generally not aware that it occurs

∙Mutations themselves are random, and natural selection does not cause them.

∙Natural selection operates where there is variation in a population. There is no natural selection simply because an environment needs it, it occurs when there is variation that is favorable over other sorts of variation.

Defend the statement that selection is reactive, and not a directed process with foresight.

Natural selection only works on the immediate, with individuals sexually selecting for and natural selection favoring individuals with certain phenotypes, without regard to possible future events. For example, in times of drought, a drought-resistant strain of a plant may become dominant, without regards to the possibility of rainy times coming.

Justify why traits/behaviors for the "good of the species" (but at the cost of an individual's fitness) would not be favored by natural selection.

∙ natural selection cannot favor traits simply "good of the species"

∙Because "survival of the fittest" takes precedence over all. Natural selection favors traits that allow for greater differential reproductive success in a population, and this comes at the cost of traits that could benefit the species

Predict how biotic and abiotic selection pressures result in changes of allele frequencies in a genetically diverse population.

∙ Abiotic: non-living aspects of the environment (temperature, pH, climate)

∙Biotic: interactions with other organisms such as predation, competition

Discuss the causes of heritable variation and the consequences of differential survival and reproduction for variation in a population.

Heritable variation allows for possibly beneficial, negative, or even neutral mutations to get filtered during each generation by natural selection--weeding out negative mutations, passing on positive and neutral ones. Without heritable variation, species would quickly fall victim to parasites who take advantage of identical genetic material in a population and evolution would not occur.

Justify why mutation is a random process to introduce alleles, but evolution by natural selection is a nonrandom process that can alter allele frequencies in a population.

Mutation happens spontaneously, but evolution is based on phenotype; a healthier phenotype that contributes to survival and higher fitness would be selected for.

Compare and contrast expected changes in allele frequency in a population depending on if that allele is under selection vs. experiencing drift.

∙Selection: based on the phenotype's effect on the organism's fitness/survival; this is not random

∙Drift: completely random and due to chance

Compare and contrast different modes of natural selection and relate them to differences in fitness of phenotypes and resulting changes in allele frequencies: (Directional, Stabilizing, Disruptive Selection)

∙Directional: an increase in a type of phenotype is always beneficial. Not found too often in populations. Happens in smaller populations before stopping.

∙ Stabilizing: an increase in a type of phenotype is only beneficial for a certain amount (ex: beak size) but any bigger/"better" will lead to a lower fitness and so it goes back down. Happens with bigger populations.

∙ Disruptive selection: Individuals of extreme phenotypes are favored, and any intermediate phenotypes are selected against (U-shaped curve)

Explain multiple ways in which a deleterious allele can persist in a population.

∙ "hiding" in heterozygous carriers at low frequency

∙ if the population is small, may be maintained (or even fixed) due to drift. in VERY small populations, the effects of drift can outweigh the effect of selection

∙ gene with deleterious allele may be closely linked to an allele of a different gene that is under strong positive selection, and increase in abundance by "hitchhiking" along. this is called "selective sweep."

∙ fitness associated with deleterious trait may change with environment

Define a biological species

∙Has to do with reproductive success; gene flow; sexual reproduction

∙Biological species concept: the definition of a species as a population or group of populations that are reproductively isolated from other groups. Members of a species have the potential to interbreed in nature to produce viable, fertile offspring but cannot interbreed successfully with members of other species.

→Limitations include fossil organisms (morphology) and the fact that not all species reproduce sexually

Define reproductive isolation and relate it to gene flow among populations

∙Reproductive isolation = cannot produce offspring w/ other species, no gene flow; when members of different populations are unable to mate and successfully reproduce

∙Isolation occur when a population has been separated long enough, so that (with the absence of gene flow) the original population has diverged to the point where descendants cannot reproduce successfully

Explain why gene flow makes speciation by reproductive isolation less likely

If a population split into two, but each new population still interacts with each other, it is less likely for those populations to speciate since they are not reproductively isolated (speciation needs reproductive isolation to occur)

Compare and contrast forms of pre-zygotic and post-zygotic reproductive isolation and be able to give examples of each.

Prezygotic reproductive isolation

∙ resulting from any combination of several mechanisms that prevent individuals of two different species from mating (prevents fertilization)

→ Habitat (wrong place)

→ Temporal (wrong time)

→ Behavioral (wrong pick up line)

→ Mechanical (doesn't fit)

→Gametic barrier (gametes can't combine)

Postzygotic reproductive isolation

∙reproductive isolation resulting from mechanisms that operate after mating of individuals of two different species occurs. The most common mechanisms are the death of hybrid embryos or reduced fitness of hybrids

→ Hybrid inviability (frog example)

→Hybrid infertility (a mule)

Contrast allopatric and sympatric speciation.

Allopatric speciation

speciation that occurs when populations of the same species become geographically isolated, often due to dispersal or vicariance

sympatric speciation

the divergence of populations living within the same geographic area into different species as the result of their genetics (not physical) isolation

Define the concept of "divergence" with respect to two recently isolated populations

∙When genetic isolation is accompanied by genetic divergence - due to genetic drift, mutation, and selection -speciation results.

∙ Dispersal: geographic barrier between populations was already there

∙Vicariance: geographic barrier splits a population that was already there

→Island-Mainland (genetic isolation)

∙The populations are free to genetically diverge, as there is no gene flow to standardize their allele frequencies

Be able to identify how genetic drift and different modes of natural selection can enhance divergence between recently isolated populations.

∙Genetic drift

→ Allele frequencies changing due to chance alone

→The larger the population, the smaller the genetic drift (the smaller the fluctuations of allele frequency)

∙ modes of natural selection: directional, disruptive, stabilizing

∙ directional

→New direction in which selection wants to favor individuals with a particular heritable trait

→ Decreases variance

∙ stabilizing

→ Most of the individuals already have the phenotype that maximizes fitness for the particular selective pressures in the environment

→Decreases variance

∙ disruptive

→ Bimodal distribution

→ Natural selection with 2 fitness optima (extremes of the range of variation and low fitness of individuals in between)

→Increases variance

directional selection

A mode of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population.

stabilizing selection

A mode of natural selection that favors phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population.

disruptive selection

A mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Increases overall genetic variation in a population.

Identify why disruptive selection is a conducive mechanism to result in sympatric speciation.

Disruptive selection is the result of when two extreme ends of a phenotype spectrum are favored by natural selection. With assortative mating, individual of the same extreme phenotype tend to mate with each other, eventually leading to divergence between both extreme phenotypes

Explain how secondary traits (such as sexually selected traits) that lead to increased reproductive isolation can increase fitness of individuals among sympatrically diverging populations.

∙ Sexually-selected traits, like all traits, are subject to fitness trade-offs: red beaks and feathers may be attractive to mates, but they also draw predators. In some species, ecological selection favors females and/or males that have "cryptic" coloration that helps them to blend in with their environments for part or all of their life cycle.

∙Sexually dimorphic traits can help to attract mates and/or deter competitors for mates

nodes

∙ in a phylogenetic tree, the point where two branches diverge, representing the point in time when an ancestral group split into two or more descendant groups; also called a fork

branches

a part of a phylogenetic tree that represents populations through time

Explain how we can use traits/characters to group related organisms

The closer the relativity of DNA sequences between two species, the more likely they are related. This also applies to traits and characters. The process of grouping organisms based on these traits is called cladistics.

Define a clade and know that clades are nested groupings of organisms, clade within clade, that group organisms by ever more distant common ancestors.

Clade: an evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a lineage

Compare and contrast shared derived traits and shared ancestral traits, and know which is used to define a clade

Shared ancestral trait

a character, based on a common ancestor that brings all clades together (beginning point of a phylogenetic tree); a trait shared by members of a particular clade and related to species beyond the clade currently considered

Shared derived traits

a character that defines a clade (based on the most recent common ancestor); a trait that evolved into the most recent common ancestor of all members of this clade; no species outside this clade possess it, so it defines the clade currently being considered

Understand that any character that is a shared derived character for one clade, can be a shared ancestral character for another clade.

Some clades consist of many branches, some may only consist of two. The more branches a clade consists of, the more and more recent common ancestors there are. So, for clades like that, a less recent ancestor (shared ancestral trait) can be the most recent ancestor (shared derived character) for clades with only a few branches.

Contrast Monophyletic, Paraphyletic, Polyphyletic groupings

Monophyletic group

∙ An evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage.

∙ a valid clade

∙ group all descendants of a common ancestor into a group

Paraphyletic group

∙ a group that includes an ancestral population and some but not all of its descendants

∙ missed some species that belong within a clade (not a valid clade)

Polyphyletic groupings

∙ groups distantly related species into an unnatural grouping (not a valid clade)

Be able to use a set of characters for different species to create a cladogram, using the principle of maximum parsimony.

∙ parsimony

→ The principle that the most likely explanation of a phenomenon is the most economical or simplest. When applied to comparison of alternative phylogenetic trees, it suggests that one requiring the fewest character changes is most likely

∙maximum parsimony means that the phylogenetic tree that minimizes the total number of character-state changes is preferred (the most simplest form possible)

Contrast homologous versus analogous characters, be able to give examples.

homologous character

∙ a character that is shared by a group of organisms because it evolved in the most recent common ancestor of that

∙ ex: four limbs of tetrapods

analogous character

∙ also called a homoplasy

∙ a character that evolved independently via convergent evolution in two unrelated lineages that make them appear more similar

∙ ex: wing of a fly, moth and bird (bc they developed independently as adaptations to a common function - flying)

Be able to identify a character as homologous versus analogous when presented with a cladogram of a lineage that displays these characters.

∙ homologous = characters of the same clade

∙analogous = characters of different clades

Explain how convergent evolution can result in analogous traits

∙ When two species of different ancestry undergo similar environmental pressures, the species will evolve in a way that they develop similar traits

∙ the independent evolution of similar traits in different species due to adaptation to similar environmental conditions and a similar way of life

Understand how DNA sequences can be used as characters in cladistic analysis.

∙ DNA sequences (or amino acid sequences encoded in genes) are powerful characters for use in cladistics because each nucleotide in the sequence is a separate character, yielding millions of characteristics

Explain the basic assumptions made in cladistic analyses, what errors can occur, what causes these errors in inferring evolutionary relationships to occur, and how to guard against errors in constructing phylogenies/cladograms.

∙ errors that can occur include paraphyletic groupings and polyphyletic groupings

∙ these are common mistakes when one creates phylogeny

∙ how to avoid: ensure that when grouping, the group consists of all descendants of a common ancestor into a group (monophyletic grouping)

Contrast proximate versus ultimate explanations

proximate explanation/causation

the immediate, mechanistic cause of a phenomenon (how it happens), as opposed to why it evolved

ultimate explanation/causation

the reason that a trait or phenomenon is thought to have evolved; the adaptive advantage of that trait

Highlight the main evolutionary changes associated with the origin of tetrapods, and tetrapod limbs in particular

Some of the selection pressures for the evolution of tetrapod limbs is the changing environment. The environment slowly developed into rainforest. The rainforest provided additional food, and this forced the fish to adapt to have tetrapod limbs to take advantage of the food source the rainforest had to offer

Define "pre-adaptations".

structures that evolved under different selection pressures that could be co-opted for a new function later

Contrast the selective pressures that tetrapod limbs originally evolved under, with what they were later co-opted for in terrestrial tetrapod lineages.

Tetrapod limbs originally evolved for use on water, but later were used to walk on land

Explain why we essentially never see the appearance of a brand-new structure "from scratch", but rather tinkering with pre-existing structures that can be co-opted for new functions.

Evolution of the tetrapod "hand" did not involve the evolution of entirely new regulatory genes, but rather involved changes in expression patterns of regulatory genes involved in growth and forewarning of developing limb buds in tetrapods

Reconstruct basic developmental organization of a common ancestor, given information about shared regulatory genes among members of descendant species.

Compare and contrast the general outline of the mammalian/avian circulatory system with that in fish, lungfish, and amphibians.

∙ vertebrate group: ray-finned fish

∙ number of circuits:

∙ presence of septum:

∙ separation of ventricle:

∙ vertebrate group: ray-finned fish

∙ number of circuits: 1

∙ presence of septum: absent

∙ separation of ventricle: absent

∙ vertebrate group: amphibians

∙ number of circuits:

∙ presence of septum:

∙ separation of ventricle:

∙ vertebrate group: amphibians

∙ number of circuits: 2

∙ presence of septum: absent

∙ separation of ventricle: absent

∙ vertebrate group: reptiles

∙ number of circuits:

∙ presence of septum:

∙ separation of ventricle:

∙ vertebrate group: reptiles

∙ number of circuits: 2

∙ presence of septum: present

∙ separation of ventricle: partial

∙ vertebrate group: mammals

∙ number of circuits:

∙ presence of septum:

∙ separation of ventricle:

∙ vertebrate group: mammals

∙ number of circuits: 2

∙ presence of septum: present

∙ separation of ventricle: complete

Be able to generate hypotheses regarding the evolutionary origin of anatomical structures given information on the phylogenetic relationships between lineages.

derived structures

refers to a character or feature found within a single lineage of a larger group; not shared with all organisms in the larger group

analogous structures

a character that evolved independently via convergent evolution in two unrelated lineages that make them appear more similar

shared ancestral structures

a trait shared by members of a particular clade AND related species beyond the clade currently considered

phylogenetic constraint

a developmental pathway in a group of organisms that can be modified by natural selection but that is difficult to reverse