Ch 23 HW

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

0.4

Part A - Calculating allele frequencies in a population The first step in testing whether a population is in Hardy-Weinberg equilibrium is to calculate the allele frequencies in the population. Remember that the frequency of an allele in a gene pool is the number of copies of that allele divided by the total number of copies of all alleles at that locus. Using the day 7 data, what is the frequency of the CG allele (p)?

0.484

Part A Which of these individuals is a homozygous genotype?

AA

Part E 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.

Part K Which of these gametes contain one or more recombinant chromosomes?

B, C, F, and G

Part A Which type of selection tends to increase genetic variation?

Disruptive selection

Part A 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

Part E - Determining whether a population is in Hardy-Weinberg equilibrium Compare the observed genotype frequencies you just calculated with the genotype frequencies expected if the population is in Hardy-Weinberg equilibrium. At day 7, is the seedling population in Hardy-Weinberg equilibrium, or is evolution occurring?

The population is in Hardy-Weinberg equilibrium.

Part B 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.

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

gene flow

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

nonsister chromatids of homologous chromosomes

Part C Genetic drift is a process based on _____.

the role of chance

Part D A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Part C 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.

true

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

2-3

Part F 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

Part E 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

Part G 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

Part B 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.

Part L This animation illustrates _____ as it occurs during _____.

crossing over ... prophase I

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

gene pool

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

genetic drift

Part F Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?

selection

Part B Using the day 7 data, what is the frequency of the CY allele (q)?

0.516

Part H - Formulating a hypothesis Homozygous CYCY individuals cannot produce chlorophyll. The ability to photosynthesize becomes more critical as seedlings age and begin to exhaust the supply of food that was stored in the seed from which they emerged. What hypothesis could explain the data for days 7 and 21?

At day 7, CYCY individuals were not being selected against because they had not used up the supply of food that was stored in the seed; by day 21, they had run out of stored food and many plants were not surviving.

Part D 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

Part C - Calculating expected genotype frequencies Next, use the Hardy-Weinberg equation (p 2 + 2pq + q 2 = 1) to calculate the expected frequencies of genotypes CGCG , CGCY , and CYCY for a population in Hardy-Weinberg equilibrium. Fill in the table with the expected frequencies for each genotype. Enter your answers to three decimal places.

The expected frequency of genotype CGCG is p 2 = 0.484 × 0.484 = 0.234. The expected frequency of genotype CGCY is 2pq = 2 × 0.484 × 0.516 = 0.499. The expected frequency of genotype CYCY is q 2 = 0.516 × 0.516 = 0.266.

Part G 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.

Part E 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.

Part I - Making a prediction How do you expect the frequencies of the CG and CY alleles to change beyond day 21?

The frequency of the CY allele will decrease, and the frequency of the CG allele will increase.

Part F Now calculate the observed frequencies of genotypes CGCG , CGCY , and CYCY at day 21. Fill in the table with the observed frequencies for each genotype at day 21. Enter your answers to three decimal places.

The observed frequency of genotype CGCG is 47÷173 = 0.272. The observed frequency of genotype CGCY is 106÷173 = 0.613. The observed frequency of genotype CYCY is 20÷173 = 0.116.

Part D - Calculating observed genotype frequencies Now that you know the expected genotype frequencies, you need to calculate the observed frequencies of genotypes CGCG , CGCY , and CYCY at day 7. Remember that the observed frequency of a genotype in a population is the number of individuals with that genotype divided by the total number of individuals. Fill in the table with the observed frequencies for each genotype at day 7. Enter your answers to three decimal places.

The observed frequency of genotype CGCG is 49÷216 = 0.227. The observed frequency of genotype CGCY is 111÷216 = 0.514. The observed frequency of genotype CYCY is 56÷216 = 0.259.

Part G Compare the genotype frequencies at day 21 to the expected frequencies and the observed frequencies at day 7. Is the seedling population at day 21 in Hardy-Weinberg equilibrium, or is evolution occurring?

The population is evolving, and there appears to be selection against genotype CYCY .

Part C 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

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

metaphase I

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

mutation