BIOL 1010 Lecture Notes - Lecture 18: Allele Frequency, Genotype Frequency, Zygosity

1. Humans and chimpanzees share several polymorphic loci. Which is the LEAST plausible explanation for this fact?

A. Balancing selection has maintained polymorphism in both species

B. Incomplete lineage sorting left polymorphic loci and those have persisted since the speciation event.

C. Interbreeding has allowed introgression of alleles at theses loci in both directions.

D. Genetic variation provided by the polymorphic alleles enhances resistance to pathogens.

2. According to the social brain hypothesis, we should expect primates living in larger social groups to have:

A. Larger brains, specifically, a neocortex of relatively larger size

B. Lager incisors and canines, to defend against more social competitors

C. Smaller brains, because many individuals can work together to solve problems

D. Great variation in brain and neocortex size, with the dominant individuals having the largest

3. You extract DNA from human bones in an ancient village buried by volcanic ash. You discover that there is an extremely high frequency of the LCT allele for lactase persistence. What might you reasonably conclude about the population?

A. This population is likely the source of the high frequency of the LCT gene in Northern Europe

B. The village could not be more than 4,500 years old

C. The members of this population likely used domesticated livestock for their milk

D. villagers had a diet rich in wheat or another domesticated crop

4. Why do populations father from Africa have more deleterious mutations in their genome?

A. Repeated bottlenecks and founder effects made drift more intense more often

B. Populations farther from Africa have been exposed to more mutagens in the environment

C. As people migrated over the globe they interbred with Neanderthals and Denisovans

D. The populations are younger, so purifying selection has not had time to purge delirious mutations from the populations.

Q1. What is the founder effect?

Sampling error that occurs during the establishment of a newpopulation by a small number of migrants.

Strong natural selection acting on the founders of a newpopulation because the environment they are now living in is sodifferent from the environment they came from.

A phenomenon named after William Founder, who observed that toppredators generally have low genetic diversity.

Rapid population growth following a bottleneck.

Q2. The effects of genetic drift are more pronounced in largerpopulations.

True

False

Q3. Inbreeding tends to increase the proportion of homozygousindividuals in a population (i.e. individuals that have two copiesof the same allele).

True

False

Q4. The effective size of a population is:

The size of an idealized randomly-mating population that is notunder selection and has the same heterozygosity as the actualpopulation.

The size of an idealized randomly-mating population that has thesame heterozygosity as the actual population, but does not loseheterozygosity over time.

The size of an idealized randomly-mating population losinghomozygosity at the same rate as the actual population.

The size of an idealized randomly-mating population losingheterozygosity at the same rate as the actual population.

Q5. Which of the following tends to reduce the effective size ofa population?

Check all that apply:

Increasing the population size.

A biased sex ratio.

Non-random mating.

Q6. If gametes from a gene pool combine randomly to make only asmall number of zygotes, the allele frequencies among the zygotesmay be different than they were in the gene pool because:

The effects of natural selection are more pronounced in smallpopulations.

The effects of genetic drift over several generations are morepronounced with small numbers of gametes.

The effects of differences in frequencies for different allelesare more pronounced with small numbers of zygotes.

The effects of sampling error are more pronounced with smallsamples.

Q7. Genetic drift is different from natural selectionbecause:

In natural selection allele frequencies change because somealleles confer higher fitness, whereas in genetic drift allelefrequencies change because of chance sampling error.

Natural selection acts primarily in large populations, whereasgenetic drift acts primarily in small ones.

Natural selection is a mechanism of evolution, whereas geneticdrift is an outcome of evolution.

Natural selection tends to cause rapid evolution, whereasgenetic drift tends to cause slow evolution.

Q8. Imagine a population evolving by genetic drift in which thefrequency of allele K is 0.65. What is the probability that at somepoint in the future allele K will drift to a frequency of 1?

Q9. A dwindling population of 1000 frogs occupies an isolatedwatershed in Costa Rica. To help preserve the species, scientistscaught 20 frogs to start a new population in a nearby watershed.This species has a gene that affects eye shape. The 1000-memberwild population has two alleles for this gene: R and r, withfrequencies 0.7 and 0.3, respectively. What will be the allelefrequencies of R and r in the 20-member founder population?

The frequencies will be 0.7 for R and 0.3 for r.

The frequencies will be 1.0 for R and 0 for r.

The expected frequencies are 0.7 for R and 0.3 for r. The actualfrequencies could be different.

The founder populations's allele frequencies will necessarily bedifferent than the source population's frequencies.

Q10. For a population containing 90 females and 10 males, whatis the effective population size, N_e ?