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Mastering Biology Chapter 23

Which of these individuals is a homozygous genotype?


All the genes in a population are that population's_____.

gene pool

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

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.

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

genetic drift

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

gene flow

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

metaphase I

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

nonsister chromatids of homologous chromosomes

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


Which of these gametes contain one or more recombinant chromosomes?

B,C,F, and G

This animation illustrates _____ as it occurs during _____.

crossing over.... prophase I

The original source of all genetic variation is _____.


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 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.


What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?


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 evolutionary forces results in adaptive changes in allele frequencies?


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.

Which of the following evolutionary forces could create new genetic information in a population?


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

What process is illustrated by this animation?

gene flow

What process is illustrated by this animation?

natural selection

Generation-to-generation change in the allele frequencies in a population is _____.


The evolutionary effects of genetic drift are greatest when _____.

the population size is small

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 is the only evolutionary mechanism that consistently leads to adaptive evolution?

natural selection

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

Which statement correctly describes the role of chance in evolution?

The ultimate source of new alleles is mutation, random changes in the nucleotide sequences of an organism's DNA.

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