Chapter 21

The reason spontaneous mutations do not have an immediate effect on allele frequencies in a large population is that: a. mutations are random events, and mutations may be either beneficial or harmful. b. mutations usually occur in males and have little effect on eggs. c. many mutations exert their effects after an organism has stopped reproducing. d. mutations are so rare that mutated alleles are greatly outnumbered by nonmutated alleles. e. most mutations do not change the amino acid sequence of a protein.

The phenomenon in which chance events cause unpredictable changes in allele frequencies is called: a. gene flow. b. genetic drift. c. inbreeding. d. balanced polymorphism. e. stabilizing selection.

Which of the following phenomena explains why the allele for sickle-cell hemoglobin is common in some tropical and subtropical areas where the malaria parasite is prevalent? a. genetic drift b. heterozygote advantage c. sexual dimorphism d. neutral selection e. stabilizing selection

The neutral variation hypothesis proposes that: a. complex structures in most organisms have not been fostered by natural selection. b. most mutations have a strongly harmful effect. c. some mutations are not affected by natural selection. d. natural selection cannot counteract the action of gene flow. e. large populations are subject to stronger natural selection than small populations.

Phenotypic characteristics that increase the fitness of individuals are called: a. mutations. b. founder effects. c. heterozygote advantages. d. adaptive traits. e. polymorphisms.

Which of the following represents an example of qualitative phenotypic variation? a. the lengths of people's toes b. the body sizes of pigeons c. human ABO blood types d. the birth weights of humans e. the number of leaves on oak trees

A population of mice is at Hardy-Weinberg equilibrium at a gene locus that controls fur color. The locus has two alleles, \(M\) and \(m .\) A genetic analysis of one population reveals that \(60 \%\) of its gametes carry the \(M\) allele. What percentage of mice contains both the \(M\) and \(m\) alleles? a. \(60 \%\) b. \(48 \%\) c. \(40 \%\) d. \(36 \%\) e. \(16 \%\)

If the genotype frequencies in a population are \(0.60 \mathrm{AA}, 0.20 \mathrm{Aa}\) and 0.20 aa, and if the requirements of the Hardy-Weinberg principle apply, the genotype frequencies in the offspring generation will be: a. \(0.60 \mathrm{AA}, 0.20 \mathrm{Aa}, 0.20\) aa. b. \(0.36 \mathrm{AA}, 0.60 \mathrm{Aa}, 0.04\) aa. c. \(0.49 \mathrm{AA}, 0.42 \mathrm{Aa}, 0.09 \mathrm{aa}\) d. \(0.70 \mathrm{AA}, 0.00 \mathrm{Aa}, 0.30 \mathrm{aa}\) e. \(0.64 \mathrm{AA}, 0.32 \mathrm{Aa}, 0.04 \mathrm{aa}\)

An Eastern European immigrant carrying the allele for TaySachs disease settled in a small village on the St. Lawrence River. Many generations later, the frequency of the allele in that village is statistically higher than it is in the immigrant's homeland. The high frequency of the allele in the village probably provides an example of: a. natural selection. b. the concept of relative fitness. c. the Hardy-Weinberg genetic equilibrium. d. phenotypic variation. e. the founder effect.

If a storm kills many small sparrows in a population, but only a few medium- sized and large ones, which type of selection is probably operating? a. directional selection b. stabilizing selection c. disruptive selection d. intersexual selection e. intrasexual selection

Most large commercial farms routinely administer antibiotics to farm animals to prevent the rapid spread of diseases through a flock or herd. Explain why you think that this practice is either wise or unwise.

In what ways are the effects of sexual selection, disruptive selection, and nonrandom mating different? How are they similar?