evolution exam 2

Each individual has two copies of a gene at a given locus and the two gene copy separate with equal probability during gamete production

What is Mendel’s law of segregation?

Alleles passed to offspring at one locus are independent from alleles passed to offspring at other loci (if unlinked)

What is Mendel’s law of independent assortment?

No, mutations occurs randomly and selection acts on mutation after they occur, which filters mutations from beneficial, harmful, or neutral

Do beneficial mutations occur in response to selective pressures?

Most mutations are neutral or deleterious (reduce fitness). Very few are beneficial

What is the fitness consequence of most mutations?

Transition

purine purine; pyridine pyridine

Transversion

purine pyridine; pyridine purine

synonymous mutations

base substitution does not change the amino acid encoded by codon (A → T)

missense mutation

base substitution that changes the amino acid encoded by codon (G → A)

nonsense mutation

base substitution that creates a stop codon where there was none before (stop) pause

in-frame mutation

an insertion or deletion that shifts reading frame by a multiple of 3 nucleotidef

frameshift mutation

an insertion or deletion that shifts the reading frame by a multiple of less than 3

Dominance only describes how an allele is expressed, not how often it appears in a population; it depends on selection, mutation, and drift. Allele frequency describes how common that allele is in the population.

How can dominant traits be rare in populations (allele frequency vs. dominance)?

Establishes what will happen over time to allele frequencies in the absence of evolutionary processes

Hard-Weinberg Model (HWM). What does it do?

Allele frequencies of a population will not change if:

• Population is infinitely large: populations are always finite

• Genotypes do no confer differences in fitness: natural selection imposes differential survival and reproduction

• There is no mutation: mutation rates have been studied and are known

• Mating is random: mating is often not random

• There is no migration: this may occasionally be true but not often

Assumptions of the HWM.

p²+2pq+q²=1 (genotype frequency)

p+q=1 (allele frequency)

Allele frequencies can be used to predict genotype frequencies

where p = the frequency of one allele at a locus, and q = the frequency of the other allele at the same locus. Hence, p+q=1

Basic understanding of how to predict genotype frequencies based on allele frequencies under the HWM. p+q=1; p^2 + 2pq + q^2 = 1

Null models are used to provide specific, quantitative conditions under which something is not expected.

Widely used across all of the sciences.

By comparing what we see in nature to what we expect if the assumptions of our null model are correct, we can identify cases where those assumptions are broken.

What is a null model?

• Do allele or genotype frequencies change between generations?

• Are genotype frequencies as we would expect under random mating?

• Chi-square

How do we test if alleles on a locus are at HW equilibrium?