Mastering Biology Chapter 23

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

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

nonsister chromatids of homologous chromosomes

Which of these individuals is a homozygous genotype?

AA

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

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

Genetic drift is a process based on _____.

the role of chance

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

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

genetic drift

What are the expected genotype frequencies in the offspring generation?

0.49 CRCR (red flowers), 0.42 CRCW (pink flowers), 0.09 CWCW (white flowers)

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

metaphase I

5. The frequency of the green allele in this beetle population is

0.6

3. In this beetle population, the total number of alleles is

20

2. That a gamete from this population carries a CW allele?

20%

7. In the offspring generation, what is the frequency of the CW allele?

20%

3. When an Rr female is crossed with an Rr male, what is the probability of producing a homozygous dominant (RR) offspring?

25%

4. What is the probability of producing a homozygous recessive (rr) offspring?

25%

5. What percentage should have the genotype CRCW?

32%

4. What percentage should have the genotype CWCW?

4%

1. According to Mendel's law of segregation, what is the probablity that a gamete (egg or sperm) from an Rr parent carries an R allele?

50%

2. What is the probability that a gamete from an Rr parent carries an r allele?

50%

5. What is the probability of producing a heterozygous (Rr) offspring?

50%

3. Of all the offspring resulting from all the matings in this population, what percentage should have the genotype CRCR?

64%

2. In this beetle population, the number of brown alleles is

8

1. What is the probability that a gamete (egg or sperm) from this population carries a CR allele?

80%

6. In the offspring generation, what is the frequency of the CR allele?

80%

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. Drag each statement into the appropriate bin depending on whether it applies to natural selection, genetic drift, or gene flow.

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 bottleneck effect -responsible for the founder 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

Consider a wildflower population with the following allele and genotype frequencies. Frequency of the CR allele: p = 0.6 Frequency of the CW allele: q = 0.4 Frequency of CRCR : 50% Frequency of CRCW : 20% Frequency of CWCW : 30% Is this population in Hardy-Weinberg equilibrium?

No, the frequency of genotype CRCW is too low.

4. The frequency of the brown allele in this beetle population is

0.4

Which of these gametes contain one or more recombinant chromosomes?

B, C, F, and G

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Consider a population of wildflowers in which the frequency of the red allele CR is p = 0.7. What is the frequency of the white allele (CW ) in this population?

0.3

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

2-3

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.

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

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.

1. To calculate the frequency of the brown allele, count the number of ________ and divide by the total number of alleles in this population.

brown alleles

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

gene pool