Chapter 23
In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?
The value of a particular characteristic; characteristics of an organism can include such traits as size and color.
Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.
directional selection
What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?
founder effect
What process is illustrated by this animation?
gene flow
Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?
genetic drift
There are 40 individuals in population 1, all with genotype A1A1, and there are 25 individuals in population 2, all with genotype A2A2. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of
genetic drift.
Generation-to-generation change in the allele frequencies in a population is _____.
microevolution
The original source of all genetic variation is _____.
mutation
What is the only evolutionary mechanism that consistently leads to adaptive evolution?
natural selection
What process is illustrated by this animation?
natural selection
According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.
sexual reproduction
The evolutionary effects of genetic drift are greatest when _____.
the population size is small
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele?
0.09
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?
0.32
What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
0.4
In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?
0.80
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?
0.81
Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?
Directional selection
Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?
Disruptive selection
Which type of selection tends to increase genetic variation?
Disruptive selection
___ can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met.
Evolution
True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.
False
Which of the following are basic components of the Hardy-Weinberg model?
Frequencies of two alleles in a gene pool before and after many random matings
Which of the following evolutionary forces could create new genetic information in a population?
Mutation
What is true of natural selection?
Mutations occur at random; natural selection can preserve and distribute beneficial mutations.
You are studying three populations of birds. Population A has ten birds, of which one is brown (a recessive trait) and nine are red. Population B has 100 birds, of which ten are brown. Population C has 30 birds, and three of them are brown. Which population is most likely to be subject to the bottleneck effect?
Population A
You are studying three populations of birds. Population A has ten birds, of which one is brown (a recessive trait) and nine are red. Population B has 100 birds, of which ten are brown. Population C has 30 birds, and three of them are brown. In which population would it be least likely that an accident would significantly alter the frequency of the brown allele?
Population B
Which of the following evolutionary forces results in adaptive changes in allele frequencies?
Selection
Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards?
Stabilizing selection
Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?
Stabilizing selection
What is true of microevolution?
It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations.
Which of the following is a true statement concerning genetic variation?
It must be present in a population before natural selection can act upon the population.
What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene?
The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2, and A2A2, respectively.
What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?
The frequency of the A1 allele is 0.3.
Which of the following statements is not a part of the Hardy-Weinberg principle?
The genotype frequencies in the offspring generation must add up to two.
True or false? The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.
True
Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer, or more, than this have reduced fitness. Which of the following terms best describes this situation?
stabilizing selection
Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating
stabilizing selection.
