Chapter 18 Part 1 - Exam 5

A population of rabbits was divided up based upon the color of their fur, represented by a single locus with two alleles (B for the dominant brown allele, and b for the recessive white allele): BB (brown fur) 100 Bb (brown fur) 88 bb (white fur) 25 Calculate the allelic frequencies of the fur color locus for this population of rabbits.

B = 0.68, b = 0.32 Allelic frequency is the number of one allele (2 × # of homozygotes + 1 × # of heterozygotes) divided by the total number of alleles (2 × # of individuals). The allelic frequency of B = (100 × 2) + (88)/(100 + 88 + 25) × 2.

If you have data on genotype frequencies at a locus for a population, what steps would you follow to determine if these genotypes are in Hardy-Weinberg equilibrium?

Calculate allele frequencies from the observed genotype frequencies, use the allele frequencies to calculate the expected number of genotypes under Hardy-Weinberg equilibrium, and conduct a chi-square test. Allele frequencies are used to calculate the expected numbers of each genotype under Hardy-Weinberg equilibrium. The chi-square test allows you to statistically evaluate whether or not the two sets of numbers match.

Which of the following will not increase genetic variation within a population?

genetic drift

You have determined that a trait within a population is not in Hardy-Weinberg equilibrium. You have also determined that mutation, migration and natural selection are not present for this trait. What factor is keeping this trait out of Hardy-Weinberg equilibrium?

genetic drift This population is undergoing genetic drift, which can keep a population out of Hardy-Weinberg equilibrium, especially if the population is small.

The forward mutation rate for the melanic form (dark grey color) in a population of peppered moths is 5 × 10-7and the reverse mutation rate is 1 × 10-9. If the population is in mutational equilibrium, what is the expected allelic frequency of the melanic form?

0.998 Allelic frequency for a trait in mutational equilibrium is equal to the forward genetic rate divided by the sum of both forward and reverse mutation rates.

If the assumptions of the Hardy-Weinberg law are met, the genotype frequencies in a population will stabilize after _____ generation(s) of random mating.

1

The sum of all genotypic frequencies always equals _____.

1

If the frequency of a particular homozygous recessive disease in a population is 1 in 10,000, what percent of the population is homozygous dominant for the wild-type trait?

98%

Why is the frequency of a heterozygote in the Hardy-Weinberg equilibrium multiplied by 2?

A heterozygote can be produced through two different combinations of egg and sperm.

In a population of diploid individuals in Hardy-Weinberg equilibrium, if the probability of the A allele is 0.6 and the probability of the a allele is 0.4, what are the genotype frequencies in the next generation?

AA = 0.36 and Aa = 0.48, aa = 0.16

In which of the following scenarios would you expect the greatest impact of genetic drift on differences in allele frequencies among a group of ten populations?

Each population starts with a size of 20 and allele frequencies of p = 0.5 and q = 0.5

True or false? A population in Hardy-Weinberg equilibrium is actively evolving.

FALSE

True or false? Mutation and recombination occur in response to an individual's need to adapt to its environment.

FALSE

True or false? Mutations do not occur, at any rate, in populations in Hardy-Weinberg equilibrium.

FALSE

From a sample of individuals the following genotypes were counted for ABO blood types where IA, IB, and i represent different alleles: IAIA (A blood type) 28 IAIB (AB blood type) 10 IBIB(B blood type) 15 IBi (B blood type) 12 IAi (A blood type) 20 ii (O blood type) 15 Calculate the allele frequencies of the ABO blood group locus for this population.

IA = 0.43, IB= 0.26, I = 0.31

Why is there typically more variation in genotype than phenotype in a population?

Mutations can be made in the genome that still result in the same protein.

From the individuals in your genetics class, the following phenotypes and corresponding genotypes were counted for tasters versus non-tasters of the chemical compound phenylthiocarbamide (PTC), where P and p represent different alleles: PP (severe tasters) 11 Pp (mild tasters) 18 pp (non-tasters) 20 Calculate the genotypic frequencies of the PTC-taste locus for this population.

PP = 0.22, Pp = 0.37, pp = 0.41 Genotypic frequency is the number of individuals with a particular genotype divided by the total number of individuals. PP = 11/(11 + 18 + 20), Pp = 18/(11 + 18 + 20), pp = 20/(11 + 18 + 20).

_____ refers to a deviation from expected results due to a limited sample size.

Sampling error

True or false? A single generation that produces Hardy-Weinberg equilibrium frequencies means that this population has not been affected by natural selection, mutation, and migration since the last time random mating took place.

TRUE

`True or false? You can use the Hardy-Weinberg law to determine whether natural selection or other selection pressures are acting upon a population at any given time.

TRUE

Why is it easier to use allelic frequency than genotypic frequency to characterize a population's gene pool?

The gene pool can be described using fewer parameters.

Migration begins between two genetically diverse populations. What will happen to the gene pools of these two populations?

The gene pools will become more similar.

Which of the following is a correct statement about the Hardy-Weinberg Law?

The law requires random mating for only the locus under consideration.

Which of the following is not an assumption of populations exhibiting Hardy-Weinberg equilibrium for a given trait?

The population is undergoing natural selection.

How is it possible for a population to have extensive molecular variation?

There are no advantages or disadvantages to one molecular variant over another.

The continuity of a population from one generation to the next can be described by the number and types of _____.

alleles

Genetic rescue is when _____.

an inbred populations genetic variation is increased, usually through the introduction of new individuals.

In which method of calculating allelic frequency would you not need to know the actual numbers of the different genotypes in the population?

calculating by genotypic frequencies

The splitting of one population into two, resulting in new species, is called _____.

cladogenesis

The influx of genes from other populations is known as _____.

gene flow

The first step required for evolution to occur is _____.

genetic variation

Inbreeding leads to a decrease in the proportion of _____ in a population.

heterozygotes

In a Mendelian population that is inbred, would the gene pool have more or less variation than a population that is not inbred?

less variation

Change in allelic frequencies can be caused by _____.

mutation genetic drift natural selection migration ALL THE ABOVE

The study of population genetics is similar to the study of evolution for all of the following reasons, except _____.

population geneticists only study populations that are affected by artificial selection.

If the probability of an egg containing the allele b is q and the probability of a sperm containing the allele b is q, then what is the probability of a gamete being homozygous for b?

q2

Sampling error produced by _____ tends to _____ of genetic drift in a population.

the founder effect; increase the effect

What actually evolves in a group of organisms?

the gene pool

The field of population genetics studies _____.

the genetic makeup of groups of individuals and how it changes through time.