Finite Populations

Question 1

Genetic Drift

Answer 1

Allele frequencies fluctuate over time in the absence of natural selection, mutation, and migration

Question 2

Effective Population Size

Answer 2

The individuals in a population who contribute to the next generation
-Effective population size may be much smaller than measured population size
-Fluctuating population size over time dramatically reduces the effective population size
-Not everyone in a population can create offspring; too young or too old

Question 3

Genetic Bottleneck

Answer 3

A population is greatly reduced in size, limiting the genetic diversity of the species

Question 4

Founder Effect

Answer 4

Reduced genetic diversity of a population because it was founded by a small # of individuals

Question 5

Neutral Theory of Molecular Evolution

Answer 5

Most variation is selectively neutral and most changes to DNA sequences over time are selectively neutral
-Variation in genomes is not largely due to selection but due to drift

Question 6

What are the effects of genetic drift on different populations?

Answer 6

-Effect of genetic drift is stronger in smaller populations
-Finite populations lead to one allele becoming fixed
-Fixation takes longer in large population
-Probability that an allele will become fixed is equal to its frequency in the population
-Some alleles are fixed while others are lost

Question 7

How to calculate heterozygosity

Answer 7

1. Heterozygosity decreases at a rate of 1/2N
2. H_offspring= (1- (1/2N)) H_parental
3. Heterozygosity (He): He= 1- (sum of each allele)^2

Question 8

How to calculate effective population size based on # of females and # of males

Answer 8

Ne=~ (4NmNf)/(Nm+Nf)
-m is male
-f is female

Question 9

How to calculate effective population size based on number of years at a certain population size

Answer 9

Ne=~ k/((1/N1)+(1/N2)+…+(1/Nk)
-k is years
-N is number in population

Question 10

Explain the relationship between selection and allele fixation compared to fixation in genetic drift

Answer 10

The probability that an allele is fixed due to selection depends on the strength of selection AND population size

Question 11

Given Ka/Ks ratio, state what type of selection is occurring

Answer 11

Ka= # of nonsynonymous substitutions per nonsynonymous site
Ks= # of synonymous substitutions per synonymous site
Ka/Ks<1; purifying selection
Ka/Ks~1; near neutrality
Ka/Ks>1; positive selection