Question 22.10

If telomeres are normally shortened after each round of replication in somatic cells (see Chapter 12), what prediction would you make about the length of telomeres in Dolly, the first cloned sheep?

Question 22.11

A drug causes the degradation of Cactus protein. What would be the effect of administering this drug to developing Drosophila embryos?

Question 22.12

What would be the effect of deleting the toll gene in Drosophila embryos?

Question 22.13

Why do mutations in bicoid and nanos exhibit genetic maternal effects (a mutation in the maternal parent produces a phenotype that shows up in the offspring, see Chapter 5), but mutations in runt and gooseberry do not? (Hint: See Tables 22.3 and 22.4.)

Question 22.14

Give examples of genes that affect development in fruit flies by regulating gene expression at the level of (a) transcription and (b) translation.

Question 22.15

Using Figure 22.6, indicate at which stage segmentation genes, homeotic genes, and egg polarity genes would have an effect on development.

658

Question 22.16

What would be the most likely effect on development of puncturing the posterior end of a Drosophila egg, allowing a small amount of cytoplasm to leak out, and then injecting that cytoplasm into the anterior end of another egg?

Question 22.17

Christiane Nüsslein-Volhard and her colleagues carried out several experiments in an attempt to understand what determines the anterior and posterior ends of a Drosophila larva (reviewed in C. Nüsslein-Volhard, H. G. Frohnhofer, and R. Lehmann. 1987. Science 238:1675-1681). They isolated fruit flies with mutations in the bicoid gene (bcd⁻). These flies produced embryos that lacked a head and thorax. When they transplanted cytoplasm from the anterior end of an egg from a wild-type female into the anterior end of an egg from a mutant bicoid female, normal head and thorax development took place in the embryo. However, transplanting cytoplasm from the posterior end of an egg from a wild-type female into the anterior end of an egg from a bicoid female had no effect. Explain these results in regard to what you know about proteins that control the determination of the anterior–posterior axis.

Question 22.18

What would be the most likely result of injecting bicoid mRNA into the posterior end of a Drosophila embryo and inhibiting the translation of nanos mRNA?

Question 22.19

What would be the most likely effect of inhibiting the translation of hunchback mRNA throughout the embryo?

Question 22.20

Molecular geneticists have performed experiments in which they altered the number of copies of the bicoid gene in flies, affecting the amount of Bicoid protein produced.

• a. What would be the effect on development of an increased number of copies of the bicoid gene?
• b. What would be the effect of a decreased number of copies of bicoid? Justify your answers.

Question 22.21

What would be the most likely effect on fruit-fly development of a deletion in the nanos gene?

Question 22.22

Give an example of a gene found in each of the categories of genes (egg-polarity, gap, pair-rule, and so forth) listed in Figure 22.13.

Question 22.23

In Chapter 1, we considered preformationism, the early idea about heredity that suggested that inside the egg or sperm is a tiny adult called a homunculus, with all the features of an adult human in miniature. According to this idea, the homunculus simply enlarges during development. What types of evidence presented in this chapter prove that preformationism is false?

Question 22.24

Explain how (a) the absence of class B gene expression produces the flower structures seen in class B mutants (see Figure 22.15c) and (b) the absence of class C gene product produces the structures seen in class C mutants (see Figure 22.15d).

Question 22.25

What would you expect a flower to look like in a plant that lacked both class A and class B genes? In a plant that lacked both class B and class C genes?

Question 22.26

What will be the flower structure of a plant in which expression of the following genes is inhibited?

• a. Expression of class B genes is inhibited in the second whorl, but not in the third whorl.
• b. Expression of class C genes is inhibited in the third whorl, but not in the fourth whorl.
• c. Expression of class A genes is inhibited in the first whorl, but not in the second whorl.
• d. Expression of class A genes is inhibited in the second whorl, but not in the first whorl.

Question 22.27

William Jeffrey and his colleagues crossed surface-dwelling Mexican tetras that had fully developed eyes with cave-dwelling blind Mexican tetras. The progeny from this cross had uniformly small eyes compared with those of surface fish (Y. Yamamoto, D. W. Stock, and W. R. Jeffrey. 2004. Nature 431:844–847). What prediction can you make about the expression of shh in the embryos of these progeny relative to its expression in the embryos of surface fish?

Question 22.28

In a particular species, the gene for the kappa light chain has 200 V gene segments and 4 J segments. In the gene for the lambda light chain, this species has 300 V segments and 6 J segments. If only the variability arising from somatic recombination is taken into consideration, how many different types of light chains are possible?

Question 22.29

Based on the information provided in Figure 22.21, what would be the likely effect of a mutation that prevented the formation of memory cells?

Question 22.30

In the book Chromosome 6 by Robin Cook, a biotechnology company genetically engineers individual bonobos (a type of chimpanzee) to serve as future organ donors for clients. The genes of the bonobos are altered so that no tissue rejection takes place when their organs are transplanted into a client. What genes would need to be altered for this scenario to work? Explain your answer.

[Ronald van der Beek/Shutterstock.]