Question 17.15

Malaria, one of the most pervasive and destructive of all infectious diseases, is caused by protozoan parasites of the genus Plasmodium, which are transmitted from person to person by mosquitoes. Plasmodium parasites are able to evade the host immune system by constantly altering the expression of their var genes, which encode Plasmodium surface antigens (L. H. Freitas-Junior et al. 2005. Cell 121:25–36). Individual var genes are expressed when chromatin structure is disrupted by chemical changes in histone proteins. What type of chemical changes in the histone proteins might be responsible for these changes in gene expression?

Question 17.16

A geneticist is trying to determine how many genes are found in a 300,000-bp region of DNA. Analysis shows that four H3K4me3 modifications are found in this piece of DNA. What might their presence suggest about the number of genes located there?

Question 17.17

In a line of human cells grown in culture, a geneticist isolates a temperature-sensitive mutation at a locus that encodes an acetyltransferase enzyme; at temperatures above 38°C the mutant cells produce a nonfunctional form of the enzyme. What would be the most likely effect of this mutation when the cells are grown at 40°C?

Question 17.18

What would be the most likely effect of deleting flowering locus D (FLD) in Arabidopsis thalania?

Question 17.19

X31b is an experimental compound that is taken up by rapidly dividing cells. Research has shown that X31b stimulates the methylation of DNA. Some cancer researchers are interested in testing X31b as a possible drug for treating prostate cancer. Offer a possible explanation for why X31b might be an effective anticancer drug.

Question 17.20

How do repressors that bind to silencers in eukaryotes differ from repressors that bind to operators in bacteria?

Question 17.21

Examine Figure 17.7. What would be the effect on transcription if a mutation occurred in the gene that encodes GAL3, so that no functional GAL3 was produced?

Question 17.22

What would be the effect of moving the insulator shown in Figure 17.8 to a position between Enhancer II and the promoter for gene B?

Question 17.23

An enhancer is surrounded by four genes (A, B, C, and D), as shown in the adjoining diagram. An insulator lies between gene C and gene D. On the basis of the positions of the genes, the enhancer, and the insulator, the transcription of which genes is most likely to be stimulated by the enhancer? Explain your reasoning.

Question 17.24

What will be the effect on sexual development in newly fertilized Drosophila embryos if the following genes are deleted?

• a. sex lethal
• b. transformer
• c. double-sex

Question 17.25

Examine Figure 17.12. What would be the effect of a mutation that eliminated the second 3′ splice site at the end of exon B in the tra pre-mRNA?

Question 17.26

Some eukaryotic mRNAs have an AU-rich element in the 3′ untranslated region. What would be the effect on gene expression if this element were mutated or deleted?

Question 17.27

A strain of Arabidopsis thaliana possesses a mutation in the APETALA2 gene, in which much of the 3′ untranslated region of mRNA transcribed from the gene is deleted. What is the most likely effect of this mutation on the expression of the APETALA2 gene?

Question 17.28

What will be the effect of a mutation that destroys the ability of poly(A)-binding protein (PABP) to attach to a poly(A) tail?

Question 17.29

Suppose a geneticist introduced a small interfering RNA (siRNA) that was complementary to the FLC mRNA in Figure 17.3. What would be the effect on flowering of Arabidopsis? Explain your answer.