Chapter 23 Exam Questions

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

Evolution is a change in a population's allele frequencies over generations.

Which of the following mechanisms can alter allele frequencies?

Natural selection, gene flow, and genetic drift can all cause microevolutio

Which example below correctly describes average heterozygosity?

Average heterozygosity refers to the average percentage of loci that are heterozygous in a population.

The human genome consists of approximately 3 billion base pairs. If humans typically differ from one another by about 3 million base pairs, what is the nucleotide variability of Homo sapiens?

Nucleotide variability in humans is about 0.1%, indicating that Homo sapiens is a fairly young species.

Which example below would most likely exhibit a cline?

Rabbits that live in colder regions tend to have smaller ears than rabbits of the same species that live in warmer regions. A cline is a graded change in a trait along a geographic axis.

Which of the following can form entirely new alleles?

Mutations

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

Meiosis

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

Duplication

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

In the Hardy-Weinberg equation, p2 represents _____.

the expected frequency of homozygous dominant individuals in the population; p = the frequency of the dominant allele (A); thus p2 represents the frequency of homozygous dominant individuals (AA: p × p = p2).

In a large population of bonobos, the frequency of the recessive allele is initially 0.1. There is no migration and no selection. What is the frequency of the dominant allele? Assume that there are two alleles of this gene.

90%; p (the frequency of the dominant allele) = 1 − q (the frequency of the recessive allele), or 0.9.

In a population in Hardy-Weinberg equilibrium, 1% of the individuals in a population show the recessive trait of a certain characteristic. In this situation, what is the value of p?

0.9; In this equation q2 = .01, q = 0.1, 1 − 0.1 = p = 0.9

In the equation for Hardy-Weinberg equilibrium, 1 represents _____.

the sum of the frequencies of the genotypes for a particular gene locus

Approximately 1 out of every 2,500 Caucasians in the United States is born with the recessive disease cystic fibrosis. According to the Hardy-Weinberg equilibrium equation, approximately what percentage of people are carriers?

If q2 equals 1/2,500, then q equals .02, p equals .98, and 2pq equals approximately .04, or 4%.

In a certain group of African people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group has the selective advantage of being more resistant to malaria (heterozygous) than those individuals who are homozygous for normal hemoglobin or for sickle-cell disease?

32%

Assume a population in Hardy-Weinberg equilibrium for a character trait with these genotypic frequencies: AA = 0.25, Aa = 0.50, and aa = 0.25. If you remove all the homozygous dominants and allow the remaining population to reproduce (again under Hardy-Weinberg conditions), what will be the frequency of homozygous dominants in the next generation?

0.11

Which of the following sets of conditions is required for Hardy-Weinberg equilibrium?

random mating, no natural selection, and a large population, no mutations and no movement of alleles into or out of the population

_____ and _____ generate variation, whereas _____ results in an adaptation to the environment.

Mutation ... sexual recombination ... natural selection

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