Question 1

Mutation may be the ultimate source of genetic variation, but sexual reproduction and similar processes like bacterial conjugation or transformation are also important in continually generating novel genetic combinations.

Accepted Answer

Mutation introduces new genetic variations, while sexual reproduction and processes like bacterial conjugation or transformation shuffle existing genes to create new combinations.

Question 2

In the early twentieth century, evolutionary biologists argued whether there was enough genetic variation in populations to explain the diversity of life by natural selection. With the advent of protein electrophoresis and DNA-level analysis, the problem turned on its head: the neutralist school arose from the idea that there was too much genetic variation to be maintained by natural selection. What are some of the arguments and observations neutralists cited to support the idea that much variation is neither favored nor disfavored by natural selection?

Accepted Answer

The answer of In the early twentieth century, evolutionary biologists...

Question 3

According to the Hardy-Weinberg principle, at equilibrium the allele frequencies are dependent on the genotypic frequencies.

Accepted Answer

The Hardy-Weinberg principle states that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences, and genotypic frequencies are dependent on allele frequencies, not the other way around.

Question 4

Two neighboring Caribbean islands harbor iguana populations. One island (island

Accepted Answer

The answer of Two neighboring Caribbean islands harbor iguana populations....

Question 5

Two populations experience equally severe bottlenecks, reducing each to one-tenth their original size. One population is in the bottleneck for one generation, and the other is in the bottleneck for five generations. You assess heterozygosity of both populations after they have been restored to their prebottleneck size. What do you expect to find, and why?

Accepted Answer

The answer of Two populations experience equally severe bottlenecks, reducing...

Question 6

The deciduous forest of eastern North America experienced dramatic changes over the past two to three centuries, transitioning from a nearly continuous forested area to increasingly patchy forest broken up by farming and development. Some species are more sensitive to severe habitat fragmentation than others; what are some characteristics that might make a species more susceptible to the effects of habitat and population fragmentation?

Accepted Answer

The answer of The deciduous forest of eastern North America...

Question 7

A selection coefficient of 1 means zero fitness.

Accepted Answer

A selection coefficient of 1 means that every individual with a certain genotype is eliminated from the population, indicating zero fitness.

Question 8

Observed genotypic frequencies in populations rarely match HW expectations exactly. Why is this so, and how can you determine if the frequencies you observe depart from HW in a biologically meaningful degree?

Accepted Answer

The answer of Observed genotypic frequencies in populations rarely match...

Question 9

Why do we expect that postzygotic isolation evolutionarily precedes prezygotic isolation in the speciation process?

Accepted Answer

The answer of Why do we expect that postzygotic isolation...

Question 10

The population mean for a given measured trait is observed to decline over the course of several generations. This is an example of disruptive selection.

Accepted Answer

Disruptive selection favors extreme values of a trait over intermediate values, leading to two or more contrasting phenotypes in the population. A decline in the population mean suggests directional selection, where one extreme is favored over the other.

Question 11

Some recessive mutations can be exceedingly debilitating or lethal when expressed in homozygotes. If their effects are so severe, why doesn't natural selection simply purge such alleles from the population completely?

Accepted Answer

The answer of Some recessive mutations can be exceedingly debilitating...

Question 12

Two closely related insect species are active at different times of day, with one diurnal and the other nocturnal. This is an example of spatial isolation.

Accepted Answer

This is an example of temporal isolation, as the two species are isolated by the timing of their activity, rather than by physical location or habitat.

Question 13

The northern elephant seal, Mirounga angustirostris, suffered a significant population bottleneck in the late nineteenth century, when hunting reduced their population size to as few as 20 individuals. It has since rebounded to several tens of thousands. The related southern elephant seal, M. leonine, was not hunted as intensively. What prediction can you make about the relative levels of heterozygosity in populations of these two species?

Accepted Answer

The answer of The northern elephant seal, Mirounga angustirostris, suffered...

Question 14

With respect to a gene with two alleles, for each generation of complete inbreeding the proportion of heterozygotes is expected to be reduced by 1/2 while the proportion of each homozygous class is expected to increase in frequency by 1/4. Explain why this is so.

Accepted Answer

The answer of With respect to a gene with two...

Question 15

In light of the fact that the assumptions of the Hardy-Weinberg principle are unrealistic (no mutation, no selection, etc.), how can the principle be useful to population geneticists?

Accepted Answer

The answer of In light of the fact that the...

Question 16

Show algebraically that under Hardy-Weinberg equilibrium, allele frequencies will not change from one generation to another.

Accepted Answer

The answer of Show algebraically that under Hardy-Weinberg equilibrium, allele...

Question 17

Populations that suffer significant reductions in number may experience two population-genetic consequences that together can hasten their decline. Which two processes are likely to act in concert in small populations, and what is their effect?

Accepted Answer

The answer of Populations that suffer significant reductions in number...

Question 18

The frequency of a recessive X-linked allele is equal to the phenotypic frequency of males exhibiting that allele.

Accepted Answer

This statement is true, as recessive X-linked alleles will only be expressed in males if they inherit the allele from their carrier mother, while females would need to inherit two copies of the allele, one from each parent. Therefore, the proportion of males exhibiting the phenotype is the same as the frequency of the recessive allele.

Question 19

Survival is the single most important process in evolution by natural selection.

Accepted Answer

While survival is certainly an important factor in natural selection, it is not the single most important process. Natural selection also depends on reproductive success, genetic variation, and environmental factors influencing which traits are advantageous in a given population.

Question 20

The Hardy-Weinberg relationship cannot be used to compute allele frequencies when one or more alleles are recessive.

Accepted Answer

The Hardy-Weinberg principle can be used to compute allele frequencies regardless of whether alleles are dominant or recessive, as it applies to all alleles in a population under certain conditions.

Quiz 1: Genetics of Bacteria and Bacteriophages