Biology 2, Chapter 23

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

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the recessive allele in this population?

0.8

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

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the dominant allele in this population?

0.2

All the genes in a population are that population's _____.

gene pool

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift

Which of the following statements correctly describe(s) characteristics of genetic drift?

it can cause allele frequencies to change at random, nit is significant in small populations, it can lead to a loss of genetic variation in a population, it can cause harmful alleles to become fixed in a population

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.

meiosis

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase I

The ease with which humans travel across the globe is likely to increase _____.

gene flow

Genetic variation _____.

must be present in a population before natural selection can act upon the population

All of the following conditions are required for Hardy-Weinberg equilibrium except __________.

natural selection

Which type of selection tends to increase genetic variation?

Disruptive selection

Which statement below is true about sexual selection?

sexual selection can result in sexual dimorphism- marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction

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

A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________.

the bottleneck effect

In the Hardy-Weinberg equation, 2pq represents __________.

the expected frequency of the heterozygous genotype

In the Hardy-Weinberg equation, q2 represents __________.

the expected frequency of the homozygous recessive genotype

A storm separates a small number of birds in a migrating population. These birds end up at a destination different from where they usually migrate and establish a new population in this new area. This is an example of __________.

the founder effect

In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.

the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up

The sickle-cell allele, which is recessive, causes anemia but confers resistance to malaria in individuals who possess it. However, homozygous recessive individuals often die from anemia but not from malaria, and homozygous dominant individuals do not have anemia but could die from malaria. Heterozygous individuals have the highest relative fitness. This is an example of __________.

the heterozygote advantage

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is __________.

the reshuffling of alleles in sexual reproduction

Genetic drift is a process based on _____.

the role of chance

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

In the context of populations, how do we define evolution?

Evolution is a change in a populations allele frequencies over generations

Natural selection leads to adaptation, but there are many organisms on Earth that exhibit characteristics that are less than ideal for their environment. Which of the following statements correctly explain(s) this?

Evolution is limited by historical constraints, Selection can act only on existing variations. Chance, natural selection, and the environment interact., Adaptations are often compromises.

Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors?

Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population

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

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.

At what level does gene variability quantify genetic variation?

Whole-gene

Which of the following is the best example of gene flow?

Wind blows pollen from one population of plants to another and cross-fertilization occurs.

The gene pool of a population consists of __________.

all the copies of every type of allele at every locus in all members of the population

If there is no gene flow, the curve shifts to the left or to the right, and the population size consequently increases over successive generations, which of the following is most likely occurring?

directional selection

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?

disruptive selection

Stabilizing selection __________.

favors intermediate variants in a population

When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of _____.

frequency-dependent selection

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency.

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

Duplication

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 sets of conditions is required for Hardy-Weinberg equilibrium?

Random mating, no natural selection, and a large population

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

In a certain group of people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group is heterozygous for the sickle hemoglobin allele?

32%

Which statement about variation is true?

All new alleles are the result of nucleotide variability.

Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium?

Allele and genotype frequencies in the population will remain constant from generation to generation.

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

Balancing selection

Antibiotic resistance in bacteria is an example of which of the following?

Directional selection

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

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

Disruptive 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 of the following would seem to be an example of neutral variation?

Human fingerprints

Which of the following can form entirely new alleles?

Mutation

In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?

Mutation led to increased genetic variation.

Point mutations in non-coding regions of DNA result in __________.

neutral variation

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes