Chapter 23 Homework

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

nonsister chromatids of homologous chromosomes

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

founder effect

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 of these gametes contain one or more recombinant chromosomes?

B, C, F, and G

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

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

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

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

gene flow

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

gene pool

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

genetic drift

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

genetic drift

Which of the following are causes of evolutionary change?

genetic drift natural selection mutation gene flow

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

Which of these individuals is a homozygous genotype?

AA

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2? 0.42

0.42

Populations evolve for many reasons. Suppose there is a population of plants that have either purple flowers or white flowers, and the allele for purple flowers is dominant. This means that plants with two purple alleles have purple flowers. Plants with one purple allele and one white allele also have purple flowers. Only plants with two white alleles have white flowers. For each event or condition described below, answer the following questions. Which mechanism of evolution is at work? How does this event affect the population's gene pool? Do the frequencies of the two alleles change, and if so, how?

1. During an extreme heat wave, plants with white flowers survive better. 2. A person uproots the five closes plants, which all happen to have white flowers. 3. A storm kills many plants at random. 4. Plants with purple flowers attract more insects, which pollinates the plants. 5. Workers from a nearby greenhouse accidentally introduce white flower seeds into this population's habitat. 1a: Natural Selection 1b: Frequency of white allele increases 2c: Genetic Drift 2d: Frequency of purple allele increases 3e: Genetic Drift 3f: Allele frequencies change but not predictably 4g: Natural Selection 4h: Frequency of purple allele increases 5i: Gene flow 5j: Frequency of white allele increases

In the beetles described in the animation, there were two alleles for color, brown and green. Suppose that you discover a very small population of these beetles, consisting of the individuals shown below. How can you calculate the frequency of each allele in this population? 1.To calculate the frequency of the brown allele, count the number of __ and divide by the total number of alleles in this population. 2.In this beetle population the number of brown alleles is __. 3.In this beetle population the total number of alleles is __. 4.The frequency of the brown allele in this beetle population is __. 5.The frequency of the green allele in this beetle population is __.

1: brown alleles 2: 8 3: 20 4: 0.4 5: 0.6

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

2-3

You read about soapberry bugs and select the correct statement describing relative fitness in these individuals.

A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age.

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.

The three major mechanisms of evolution differ in how they work, and as a result often have different effects on a population. Review your understanding of natural selection, genetic drift, and gene flow by sorting the statements below into the correct bins.

Natural Selection: -Consistently causes a population to become better adapted to its environment -A result of differential success in reproduction -Cannot cause a harmful allele to become more common Genetic Drift: -Responsible for the founder effect -Responsible for the bottleneck effect -Causes allele frequencies to fluctuate randomly Gene flow -Can introduce new alleles into a population's gene pool -A result of the movement of fertile individuals or their gametes

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.

In evolutionary terms, an organism's fitness is measured by its

contribution to the gene pool of the next generation

Natural selection changes allele frequencies because some _______ survive and reproduce more successfully than others.

individuals

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

metaphase I

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

microevolution

The original source of all genetic variation is

mutation Mutation is, in itself, very important to evolution because it is the original source of the genetic variation that serves as the raw material for evolution.

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

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