Chapter 21: biology

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 population of 200 mice, brown fur is dominant to gray fur. If 120 of the 200 mice have brown fur, what is the frequency of mice that are heterozygous?

0.46

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus,

The alleles frequency shouldn't change from one generation to the next but its representation in homozygous and heterozygous genotypes may change

In seedcracker finches from Cameroon, small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?

directional selection

What is the result of adaptive evolution?

increase in frequency of alleles that provide reproductive advantage

Sexual dimorphism is most often a result of

intersexual selection

Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then

sexual dimorphism was developing over time in these species.

Heterozygote advantage should be most closely linked to which of the following?

stabilizing selection

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

When evolution occurred on the Galápagos Islands, the finch beaks

varied in size across the population and sometimes conferred benefits in feeding, survivorship, and reproduction that were passed down to surviving offspring.

What is the founder effect?

when a few individuals become isolated from a larger population and their gene pool differs from that source population

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

Phenylketonuria (PKU) is a birth defect that causes an amino acid called phenylalanine to build up in the body. The frequency of individuals born in a population with PKU is q2. There is one PKU (q2) birth per 10,000 births. The frequency of the recessive allele for PKU in this population is q = 0.01. The frequency of the dominant allele in this population is p = 1 - q = 0.99. What is the frequency of carriers (2pq) in this population?

2%

Why is the Hardy-Weinberg model useful?

It allows you to calculate genotype frequencies of a population and compare them to what was expected under the assumptions.

Which of the following is correct about genetic variation?

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

Why don't similar genotypes always produce the same phenotype?

Phenotypes can vary depending upon environment

Mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology. In Tibet, for example, people have broader arteries and capillaries. In the Andes, they can dissolve more oxygen into their blood. These different traits of people who live in high altitudes illustrate

adaptive evolution

What is the Hardy-Weinberg equation?

an assessment of evolution at a particular locus

How can gene flow improve adaptation of population?

beneficial alleles are transferred to a new population

How did Mendel's model of inheritance help explain Darwin's theory of natural selection?

by proposing a mechanism of how organisms could transmit discrete, heritable units to offspring

Evolution of a gene

can happen whenever any of the conditions for Hardy-Weinberg equilibrium are not met for that particular gene

Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing

gene flow

The Hardy-Weinberg equation p2 + 2pq + q2 = 1 allows you to calculate

genotype frequencies

In the formula for determining a population's genotype frequencies, the 2 in the term 2pq is necessary because

heterozygotes can come about in two ways based upon parental gametes.

It is estimated by a wide body of scientists that in recent decades we have begun another mass extinction event on Earth. Amphibians in particular have been in decline, sometimes due to climate change, and they therefore provide a possible early sign of dramatic biodiversity change to come. With respect to climate change and natural selection acting upon a population of one species of frog in a tropical rain forest, mutations of DNA sequences of the frog genome that are inherited by offspring

may have no effect at all, be beneficial, or be harmful.

Which of the following consistently improves the degree to which organisms are well suited for life in their environment?

natural selection