CHAPTER 11 Test Your Knowledge

Driving Question 1

By answering the questions below and studying Infographics 11.1, 11.2, and 11.3, you should be able to generate an answer to the broader Driving Question above.

KNOW IT

How do the two alleles of the CFTR gene in a lung cell differ?

a. They were inherited from different parents.

b. One is on chromosome 7 and one is on chromosome 3.

c. Only one is expressed.

d. all of the above

e. There is no difference because they are both the same gene.

Consider a liver cell.

a. How many chromosomes are present?

b. How many alleles of each gene are present?

Consider a gamete.

a. How many chromosomes are present?

b. How many alleles of each gene are present?

USE IT

A diploid cell of baker’s yeast has 32 chromosomes. How many chromosomes are in each of its haploid spores?

a. 32

b. 16

c. 8

d. 64

e. 1

In diploid organisms, having two homologues of each chromosome can be beneficial if one allele of a gene encodes a nonfunctional protein. Can haploid organisms survive the presence of nonfunctional alleles? Explain your answer.

From which parent did Emily inherit cystic fibrosis? Explain your answer.

Driving Question 2

By answering the questions below and studying Infographics 11.3, 11.4, and 11.5, you should be able to generate an answer to the broader Driving Question above.

KNOW IT

A human female has _________ chromosomes in each skin cell and _________ chromosomes in each egg.

a. 46; 46

b. 23; 46

c. 46; 23

d. 23; 23

e. 92; 46

A woman is heterozygous for the CF-associated gene (the alleles are represented here by the letters A and a). Assuming that meiosis occurs normally, which of the following represent eggs that she can produce?

a. A

b. a

c. Aa

d. AA

e. aa

f. A or a

g. A, a, or Aa

Draw a maternal version of chromosome 7 in one color and a paternal version of chromosome 7 in another color. Maintaining this color distinction, now draw a possible version of chromosome 7 that could end up in a gamete following meiotic division.

USE IT

An alien has 82 total chromosomes in each of its body cells. The chromosomes are paired, making 41 pairs. If the alien’s gametes undergo meiosis, what are the number and arrangement (paired or not) of chromosomes in one of its gametes? Give the reason for your answer.

Describe at least two major differences between mitosis (discussed in Chapter 9) and meiosis.

If meiosis were to fail and a cell skipped meiosis I, so that meiosis II was the only meiotic division, how would you describe the resulting gametes?

Driving Question 3

By answering the questions below and studying Infographics 11.7, 11.8, and 11.9, you should be able to generate an answer to the broader Driving Question above.

KNOW IT

What is the genotype of a person with CF?

a. homozygous dominant

b. homozygous recessive

c. heterozygous

d. any of the above

e. none of the above

Strictly on the basis of the following CFTR genotypes, what do you predict the phenotype of each person to be?

a. heterozygous

b. homozygous dominant

c. homozygous recessive

How many copies of the CF-associated allele does a person with CF have in one of his or her lung cells? How does this compare to someone who is a carrier for CF? How does it compare to someone who is homozygous dominant for the gene CFTR?

Women can inherit alleles of a gene called BRCA1 that makes puts them at higher risk for breast cancer. The alleles associated with elevated cancer risk are dominant. Of the genotypes listed below, which carries the lowest genetic risk of developing breast cancer?

a. BB

b. Bb

c. bb

d. BB and Bb carry less risk than bb.

e. All carry equal risk.

USE IT

A person has a heterozygous genotype for a disease gene and no disease phenotype. Does this disease have a dominant or a recessive inheritance pattern?

Assume that Emily (who has CF) decides to have children with a man who does not have CF and who has no family history of CF.

a. What combination of gametes can each of them produce?

b. Place these gametes on a Punnett square and fill in the results of the cross.

c. On the basis of the Punnett square results, what is the probability that they will have a child with CF?

d. On the basis of the Punnett square results, what is the probability that they will have a child who is a carrier for CF?

From the discussion in this chapter, why might a person with a homozygous recessive CFTR genotype have a somewhat different phenotype from someone who also has a homozygous recessive CFTR genotype?

Phenylketonuria is considered to be an inborn error of metabolism. It is a recessive genetic condition in which the enzyme that breaks down the amino acid phenylalanine is defective or missing. Testing of all newborns allows this condition to be detected at birth. A special diet that severely minimizes phenylalanine (e.g., by avoiding diet sodas and most usual sources of protein) can treat the condition. If two carriers of both cystic fibrosis and phenylketonuria were to have a child, what is the probability that the child will have a. both cystic fibrosis and phenylketonuria?

b. cystic fibrosis and be a carrier for phenylketonuria?

c. neither condition?

d. neither condition and not be a carrier for either?

Driving Question 4

By answering the questions below and studying Infographics 11.6, 11.7, 11.8, and 11.9, you should be able to generate an answer to the broader Driving Question above.

KNOW IT

Can cystic fibrosis be diagnosed prenatally by examining the fetal chromosomes (as shown in the inset in Infographic 11.2)? Why or why not?

INTERPRETING DATA

Ivacaftor (trade name Kalydeco) is a drug designed to enhance the activity of the CFTR protein encoded by the G55lD allele. The protein encoded by this allele is present in the cell membrane, but it is not very active. The drug has been shown in laboratory studies to enhance the activity of this protein. To determine if ivacaftor has an impact on disease symptoms in people with cystic fibrosis, the drug was tested in a randomized, double-blind clinical trial.

a. From the information provided here and in the graph below, describe the experimental design of the trial. Include who the participants were, how participants were assigned to the experimental and the control group, and what treatment(s) were given to participants in each group. Why was it important that this was a blind trial?

b. Before treatment started, baseline measurements of lung function were obtained. One of these measurements is the amount of air that a participant can forcibly exhale from the lungs in 1 second (expressed as % of total lung volume). This measurement is known as the predicted FEV. The drug was given to the experimental group every 12 hours, and the predicted FEV was measured. The results are shown in the graph. The average value of N (the number of subjects) is shown for each group, as well as the variability of the measurement (indicated by error bars, vertical lines extending above and below the data point for each average value).
How soon did the experimental group experience an improvement in lung function as measured by predicted FEV?
How long was the improvement sustained?
By the end of the study, what was the absolute improvement of the experimental group relative to baseline?

c. The ?F508 allele causes the CFTR protein to be absent from the cell membrane. Is ivacaftor likely to be a viable treatment for patients whose CF is caused by this allele? Why or why not?

SOURCE: Ramsey, B. W., et al. (2011) A CFTR potentiator in patients with cystic fibrosis and the G551D mutation. Figure 1A. New England Journal of Medicine 365:1663–1672.