Question 11.17

The introduction to this chapter discussed a study of telomere length in Romanian children. The study demonstrated that children raised in orphanages had shorter telomeres than children raised in foster homes. What effect, if any, do you think having shorter telomeres in childhood might have on adult life?

Question 11.18

Compare and contrast prokaryotic and eukaryotic chromosomes. How are they alike and how do they differ?

Question 11.19

(a) In a typical eukaryotic cell, would you expect to find more molecules of the H1 histone or more molecules of the H2A histone? Explain your reasoning. (b) Would you expect to find more molecules of H2A or more molecules of H3? Explain your reasoning.

322

Question 11.20

Based on the DNA sensitivity to DNase I illustrated in Figure 11.7, which type of chicken hemoglobin (embryonic or adult) is likely produced in highest quantity at the following tissues and developmental stages?

• a. Erythroblasts during the first 24 hours.
• b. Erythroblasts at day 5
• c. Erythroblasts at day 14
• d. Brain cells throughout development

Question 11.21

Suppose that a researcher briefly added radioactively labeled uridine to the Drosophila larva whose polytene chromosome is shown in Figure 11.6. Label on the figure where you would expect to see accumulation of radioactive uridine.

Question 11.22

A diploid human cell contains approximately 6.4 billion base pairs of DNA.

• a. How many nucleosomes are present in such a cell? (Assume that the linker DNA encompasses 40 bp.)
• b. How many histone proteins are complexed to this DNA?

Question 11.23

Would you expect to see more or less acetylation in regions of DNA that are sensitive to digestion by DNase I? Why?

Question 11.24

Gunter Korge examined several proteins that are secreted from the salivary glands of Drosophila melanogaster during larval development (G. Korge. 1975. Proceedings of the National Academy of Sciences of the United States of America 72:4550–4554). One protein, called protein fraction 4, was encoded by a gene found by deletion mapping to be located on the X chromosome at position 3C. Korge observed that, about 5 hours before the first synthesis of protein fraction 4, an expanded and puffed-out region formed on the X chromosome at position 3C. This chromosome puff disappeared before the end of the third larval instar stage, when the synthesis of protein fraction 4 ceased. He observed that there was no puff at position 3C in a special strain of flies that lacked secretion of protein fraction 4. Explain these results. What is the chromosome puff at region 3 and why does its appearance and disappearance roughly coincide with the secretion of protein fraction 4?

Question 11.25

Suppose a chemist develops a new drug that neutralizes the positive charges on the tails of histone proteins. What would be the most likely effect of this new drug on chromatin structure? Would this drug have any effect on gene expression? Explain your answers.

Question 11.26

Which of the following two molecules of DNA has the lower melting temperature? Why?

Question 11.27

In a DNA hybridization study, DNA was isolated from a particular species, labeled with ³²P, and sheared into small fragments (S. K. Dutta et al. 1967. Genetics 57:719–727). Hybridizations between these labeled fragments and denatured DNA from different species were then compared. The following table gives the percentages of labeled wheat DNA that hybridized to DNA molecules of wheat, corn, radish, and cabbage.

What do these results indicate about the evolutionary differences among these organisms?

Question 11.28

A wheat plant that is light green in color is found growing in a field. Biochemical analysis reveals that chloroplasts in this plant produce only 50% of the chlorophyll normally found in wheat chloroplasts. Propose a set of crosses to determine whether the light-green phenotype is caused by a mutation in a nuclear gene or in a chloroplast gene.

Question 11.29

A rare neurological disease is found in the family illustrated in the following pedigree. What is the most likely mode of inheritance for this disorder? Explain your reasoning.

Question 11.30

Assume that the disorder shown in the pedigree in the Worked Problem on p. 313 is a rare disease that results from a defect in mitochrondrial DNA. If individual III-8 has a daughter, what is the probability that the daughter will inherit the muscle disorder from her affected parent?

323

Question 11.31

Fredrick Wilson and his colleagues studied members of a large family who had low levels of magnesium in their blood (see the pedigree below). They argued that this disorder of magnesium (and associated high blood pressure and high cholesterol) is caused by a mutation in mtDNA (F. H. Wilson et al. 2004. Science 306:1190–1194).

• a. What evidence suggests that a gene in the mtDNA is causing this disorder?
• b. Could this disorder be caused by an autosomal dominant gene? Why or why not?

[After F. H. Wilson et al. 2004. Science 306:1190–1194.]

Question 11.32

In a particular strain of Neurospora, a poky mutation exhibits biparental inheritance, whereas poky mutations in other strains are inherited only from the maternal parent. Explain these results.

Question 11.33

A scientist collects cells at various points in the cell cycle and isolates DNA from them. Using density-gradient centrifugation, she separates the nuclear and mtDNA. She then measures the amount of mtDNA and nuclear DNA present at different points in the cell cycle. On the following graph, draw a line to represent the relative amounts of nuclear DNA that you expect her to find per cell throughout the cell cycle. Then, draw a dotted line on the same graph to indicate the relative amount of mtDNA that you would expect to see at different points throughout the cell cycle.

Question 11.34

In 1979, bones found outside Ekaterinburg, Russia, were shown to be those of Tsar Nicholas and his family, who were executed in 1918 by a Bolshevik firing squad in the Russian Revolution (see the introduction to Chapter 14). To prove that the skeletons were those of the royal family, mtDNA was extracted from the bone samples, amplified by PCR, and compared with mtDNA from living relatives of the tsar’s family.

• a. Why was DNA from the mitochondria analyzed instead of nuclear DNA? What are some of the advantages of using mtDNA for this type of study?
• b. Mitochrondrial DNA from which living relatives would provide useful information for verifying that the skeletons were those of the royal family?

Question 11.35

Antibiotics such as chloramphenicol, tetracycline, and erythromycin inhibit protein synthesis in eubacteria but have no effect on protein synthesis encoded by nuclear genes. Cycloheximide inhibits protein synthesis encoded by nuclear genes but has no effect on eubacterial protein synthesis. How might these compounds be used to determine which proteins are encoded by mitochondrial and chloroplast genomes?