Exam III - Intro to Evolution

What does the Hardy Weinberg Model assume?

That the population is not evolving

What is the Hardy Weinberg Model used to prove?

This null model is used to prove that populations are evolving

When is a population/gene in equilibrium?

When a gene/population is not changing over time in terms of allele frequencies

When is a population/gene NOT in equilibrium mathematically and what process is used to confirm/refute this?

When observed genotype counts are significantly different from expected counts, Chi squared test

What is the Chi squared formula?

Summation of (observed-expected)^2/(expected)

When is a population evolving?

If the Chi squared test is greater than the cut off

What are the 5 assumptions of the Hardy Weinberg model?

No mutations, no selection, no gene flow, random mating, infinite population size

What are the 5 evolutionary forces?

Mutation, selection, gene flow, non-random mating, genetic drift

What is the relationship between macroevolution and microevolution?

Microevolutionary processes are the process of change (factors that influence allele changes between generations) and macroevolution is the resulting pattern of change (as these generational changes accumulate over long periods of time populations diverge and new species can arise)

What is gene flow?

Transfer of genetic variation from one population to another

What does the Island continent model assume?

That gene flow occurs in only one direction from a donor population to a recipient population

What factors affect the rate of change of allele frequencies within gene flow?

Starting frequencies, migration rate, size of the island, and distance

Gene flow is _____

Homogenizing

What does it mean that gene flow is homogenizing?

Gene flow makes island species look like continental species over time

What are the two types of non random mating?

Disassortative mating, assortative mating

Which type of mating maintains diversity, increases heterozygotes, and decreases homozygotes?

Disassortative mating

Which type of mating decreases diversity, decreases heterozygotes, and increases homozygotes?

Assortative mating

Why does one allele tend to become fixed during assortative mating?

Random genetic drift

True or False: There can be only 2 alleles within a population

False, there can be more than two alleles for a gene in a population but only 2 alleles within an individual

True or False: Equilblirum is when an allele has been fixed

False, an allele is fixed when it is the only allele present for a gene in the entire population, while equilibrium is when a gene does not change over time

Genetic drift is when _____

Random changes in allele frequencies occur over time simply because populations are finite

What does genetic drift tend to do?

Fix alleles

Why can genetic drift result in “bad” alleles becoming fixed?

Because evolution does not occur based on need

Which populations are more likely to experience genetic drift and at a faster pace?

Smaller populations

Which populations are more prone to random sampling errors?

Small populations

What is the Bottleneck effect?

When a population experiences a drastic reduction in size resulting in a loss of genetic and phenotypic variation

True or False: If a population size increases after experiencing the Bottleneck effect it will be accompanied by greater genetic diversity as well

False, an increase in the size later of a population after experiencing the Bottleneck effect will not result in an increase in genetic variation as well

Why is variation so important for a population’s health?

Selection chooses between variation and selection usually makes a population better

Why is it important to maintain variation?

It takes a long time for new variation to accumulate and if you have no variation you cannot make a population better

What is genetic diversity limited to within the Founder effect?

Genetic diversity limited to what is found in the founding individuals

When does the Founder effect occur?

When a small number of individuals from a “source” population start a new population

What are 2 causes of the Bottleneck effect?

Natural disasters and humans (over hunting, deforestation, pollution)

True or False: Populations can only experience one evolutionary force at a time

False, populations can experience multiple evolutionary forces together that might be competing with each other

How does genetic drift affect a population graph?

Causes “noise” (allele frequency bouncing up and down)

What occurs in small populations with heterozygote advantages?

Alleles are usually still fixed/lost due to genetic drift

What occurs in large populations with heterozygote advantages?

Both alleles are maitnained and more heterozygotes are produced

How does selection impact variation?

Selection usually decreases genetic variation

Selection is _____

Non random because it favors certain traits/alleles

When does selection not decrease variation?

During disruptive selection

How does genetic drift impact variation?

Genetic drift decreases genetic variation

Genetic drift is _____

Random

How does gene flow impact variation

Gene flow (usually large → small population) could increase or decrease genetic variation

What does genetic flow depend on when analyzing its impact on variation?

Depends on what variation is present in each population and whether there are opposing forces, like selection

How does mutation impact variation?

Mutation increases genetic variation (source of all new variation!)

How does assortative mating impact variation?

Assortative mating decreases variation (reduces heterozygosity)

How does disassortative mating impact variation?

Disassortative mating maintains variation (creates heterozygotes)

What is the difference between primary and secondary literature?

Primary literature is a first hand account of the time period studied, while secondary research is primary research that has been taken, summarized, analyzed, or interpreted

What is the primary difference between marsupials and placental mammals?

Marsupials raise newborn offspring inside an external pouch, while placenta mammals complete embryo development inside the mother

What is exaptation?

The shift in function of a trait acquired during evolution

What should happen to the number of alleles for any gene in a small population over time?

Decrease due to fixation/loss (ultimately loss of diversity)

What should happen to heterozygosity as genetic drift occurs?

Decreases (genetic drift leads to greater fixation leads to greater homozygosity in turn less heterozygosity)

What is the general relationship between population size, drift, and heterozygosity?

Population size decreases, genetic drift increases, and heterozygosity decreases

What is population structure?

The presence of a systematic difference in allele frequencies between subpopulations or the absence of gene flow

How do populations reach population structure?

By experiencing a lack of gene flow and eventually becoming genetically different

What is the HW EQ cutoff?

3.841