UW Biology 180 Exam 2

Hardy-Weinberg principle

Allele frequencies will remain constant from generation to generation in an ideal population (one that is not affected by evolutionary forces)

What are the 5 assumptions of Hardy-Weinberg principle?

1.) Random mating

2.) No mutation

3.) No gene flow

4.) No genetic drift (assumes large population)

5.) No selection

How does Hardy-Weinberg serve as a null hypothesis?

It represents a scenario where no evolution is occurring (that allele frequencies are not changing)

How to interpret p-value in regards to Hardy-Weinberg?

If p-value is low (

What does it mean if a population is deviating from Hardy-Weinberg principle/if p-value is less than 5%?

Suggests that at least one evolutionary mechanism is at play: mutation, selection, genetic drift or gene flow.

How to use hardy-weinberg in testing?

Calculated observed allele frequencies from real data. Use hardy-weinberg equation to predict expected allele frequencies under equilibrium. Use tests like chi-square to compare expected vs observed results. If p-value < 0.05 (the difference in expected and results is accurate) then you reject the null hypothesis/reject hardy-weinberg, meaning evolution is likely occurring.

What are the 4 sources of genetic variation?

1.) mutation

2.) independent assortment

3.) recombination (+crossing over)

4.) outcrossing

What is outcrossing?

Reproducing across different individuals. Allows for more genetic variation/diversity.

Is it possible for mean to change without allele frequency changing?

No, in order for mean to change there has to be some shift in allele frequency.

With respect to fitness, drift is:

random

What happens when drift continues, generations after generations (especially in small populations)?

Loss or fixation

What is loss/fixation?

When a fixed/favored allele reaches 100% frequency and a deleterious/unfavored allele reaches 0% frequency.

Why is drift a concern for endangered species?

An endangered species (by def) is a small population, so any mating that occurs has the potential of having huge allele shifts in a population.

What do the genetic variation sources explain?

Explains why we don't always see the most fit trait as the only trait in a population

What is a t-test?

A t-test compares the means of two groups of data on a continuous variable, while considering a categorical variable with only two categories. (1 contin. and 1 categ.).

What is a chi-square test?

Compares the observed frequencies and expected frequencies of two categorical variables.

How do you interpret R^2 tests?

___% of the variation in __(insert your y-variable)__ can be explained by variation in __(insert your x-variable)__.

How is p-value represented in a regression model? How would you interpret this.

The slope of the line. Assuming the null hypothesis is true, there is a __% chance that the slope of the best-fit line will be what we saw or greater.

What is purifying selection?

Natural selection against deleterious alleles (alleles that function poorly and lower fitness of an individual).

New definition of evolution:

Evolution is the change in allele frequency in a population over time

Different types of selection and what it does to mean/variation:

1.) **Directional (mean changes and variation decreases--loss/fixation occurs)

2.) **Stabilizing (variation decreases, mean stays the same)

3.) Disruptive (variation increases)

4.) Balancing

What is directional about directional selection? What happens to the variation?

The mean shifts/changes. Variation decreases.

Why is mutation considered the ultimate source of genetic variation?

Only mutation introduces new alleles.

What is genetic drift

A change in allele frequency due to chance.

What does it mean when mutations are deleterious versus beneficial?

Deleterious means mutation lowers fitness. Beneficial increases fitness.

Which evolutionary mechanisms introduces RANDOM component to evolution and why? Which is NON-random?

Mutation (does not occur based on fitness, just happens) and genetic drift (by definition, it is change in allele frequency by chance). Natural selection is not random (differential reproductive success based on different heritable traits).

What is the founders effect?

When a group of individuals immigrates to a new geographic area and establishes a new population

What is the bottleneck effect?

When a large population experiences a sudden reduction in size (and allele diversity).

How significant is mutation in evolution?

By itself, it is not a very significant mechanism of evolution (can be more so in bacteria and archaea) but it can have VERY large effects when combined with gene flow, genetic drift and selection. WITHOUT MUTATIONS EVOLUTION WOULD EVENTUALLY STOP.

In regression analysis, what is "best" about the line of best-fit?

It fits the data most accurately (minimizes a measure of the overall distance from the line to the datapoints).

In a regression analysis, what does the slope of the line of best fit represent?

How much the y variable tends to change with a 1-unit change in the x variable.

What is linear regression?

Statistical method used to describe the relationship between two variables by fitting a linear equation to observed data. The model predicts the value of a dependent variable (Y) based on the value of one or more independent variables (X).

What is standard error and how does sample size affect it?

Standard error (SE) is a measure of how much the sample mean (or another statistic) is expected to vary from the true population mean. The greater the sample size, the smaller the standard error.

Genetically, does gene flow make populations more alike, more dissimilar, or no impact?

It makes populations more ALIKE. Flow makes them more similar over time (comes close to 50/50).

In recipient population, what happens to fitness?

It depends on the environment it is in and the conditions it is under: some new alleles can confer higher fitness, lower fitness or NO impact on fitness at all.

How is gene flow affecting human populations?

Gene flow is the highest it's ever been in human population (with transportation) --> humans are becoming more alike over time.

Non-random mating

Inbreeding (breeding with similarly related individuals); MOST extreme is self fertilization.

Why does inbreeding depression occur?

Accumulation of deleterious recessive alleles (in the homozygous recessive allele populations)

How does inbreeding affect allele frequencies with a A1A2 plant that self fertilizes?

They stay the same/does not affect allele frequencies.

How does inbreeding affect genotype frequencies with a A1A2 plant that self fertilizes?

Increases the number of homozygotes (our original population was ONLY heterozygotes but after there were homozygotes and heterozygotes).

Why might it be advantageous for plants to be able to self?

If it is hard to reproduce with others it can be helpful to just self reproduce, but also in some environments, those with deleterious alleles are killed off so there's no worry of deleterious accumulation.

When can you say there is causation? When can you not?

When you have conducted an experiment on it—cannot if you just did observational research.

How does gene flow affect genetic variation and fitness?

Gene flow increases genetic variation with immigration until the point where the 2 populations (flowing with each other) are equal in variation BUT it *could decreases during emigration because you are losing alleles. It is random with respect to fitness (it depends).

How does drift affect genetic variation?

Drift lowers variation on average (because of the random subsets it is unlikely that the new subsets chosen represent all of the diversity found in the original population).