In Figure 13-2, the transplantation of certain regions of embryonic tissue induces the development of structures in new places. What are these special regions called, and what are the substances they are proposed to produce?

In Figure 13-5, two different methods are illustrated for visualizing gene expression in developing animals. Which method would allow one to detect where within a cell a protein is localized?

Figure 13-7 illustrates the expression of the Ultrabithorax (Ubx) Hox protein in developing flight appendages. What is the relationship between where the protein is expressed and the phenotype resulting from the loss of its expression (shown in Figure 13-1)?

In Figure 13-11, what is the evidence that vertebrate Hox genes govern the identity of serially repeated structures?

As shown in Figure 13-14, what is the fundamental distinction between a pair-rule gene and a segment-polarity gene?

In Table 13-1, what is the most common function of proteins that contribute to pattern formation? Why is this the case?

In Figure 13-20, which gap protein regulates the posterior boundary of eve stripe 2? Describe how it does so in molecular terms.

As shown in Figure 13-22, how many different transcription factors govern where the Distal-less (Dll) gene will be expressed?

As shown in Figure 13-26, the Sonic hedgehog gene is expressed in many places in a developing chicken. Is the identical Sonic hedgehog protein expressed in each tissue? If so, how do the tissues develop into different structures? If not, how are different Sonic hedgehog proteins produced?

Engrailed, even-skipped, hunchback, and Antennapedia. To a Drosophila geneticist, what are they? How do they differ?

Describe the expression pattern of the Drosophila gene eve in the early embryo.

Contrast the function of homeotic genes with that of pair-rule genes.

When an embryo is homozygous mutant for the gap gene Kr, the fourth and fifth stripes of the pair-rule gene ftz (counting from the anterior end) do not form normally. When the gap gene kni is mutant, the fifth and sixth ftz stripes do not form normally. Explain these results in regard to how segment number is established in the embryo.

Some of the mammalian Hox genes have been shown to be more similar to one of the insect Hox genes than to the others. Describe an experimental approach that would enable you to demonstrate this finding in a functional test in living flies.

The three homeodomain proteins Abd-B, Abd-A, and Ubx are encoded by genes within the Bithorax complex of Drosophila. In wild-type embryos, the Abd-B gene is expressed in the posterior abdominal segments, Abd-A in the middle abdominal segments, and Ubx in the anterior abdominal and posterior thoracic segments. When the Abd-B gene is deleted, Abd-A is expressed in both the middle and the posterior abdominal segments. When Abd-A is deleted, Ubx is expressed in the posterior thorax and in the anterior and middle abdominal segments. When Ubx is deleted, the patterns of Abd-A and Abd-B expression are unchanged from wild type. When both Abd-A and Abd-B are deleted, Ubx is expressed in all segments from the posterior thorax to the posterior end of the embryo. Explain these observations, taking into consideration the fact that the gap genes control the initial expression patterns of the homeotic genes.

What genetic tests allow you to tell if a gene is required zygotically or if it has a maternal effect?

In considering the formation of the A–P and D–V axes in Drosophila, we noted that, for mutations such as bcd, homozygous mutant mothers uniformly produce mutant offspring with segmentation defects. This outcome is always true regardless of whether the offspring themselves are bcd+/bcd or bcd/bcd. Some other maternal-effect lethal mutations are different, in that the mutant phenotype can be “rescued” by introducing a wild-type allele of the gene from the father. In other words, for such rescuable maternal-effect lethals, mut⁺/mut animals are normal, whereas mut/mut animals have the mutant defect. Explain the difference between rescuable and nonrescuable maternal-effect lethal mutations.

Suppose you isolate a mutation affecting A–P patterning of the Drosophila embryo in which every other segment of the developing mutant larva is missing.

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How does the Bicoid protein gradient form?

In an embryo from a homozygous Bicoid mutant female, which class(es) of gene expression is (are) abnormal?

Gene X is expressed in the developing brain, heart, and lungs of mice. Mutations that selectively affect gene X function in these three tissues map to three different regions (A, B, and C, respectively) 5′ of the X coding region.

Why are regulatory mutations at the mouse Sonic hedgehog gene dominant and viable? Why do coding mutations cause more widespread defects?

A mutation occurs in the Drosophila doublesex gene that prevents Tra from binding to the dsx RNA transcript. What would be the consequences of this mutation for Dsx protein expression in males? In females?

You isolate a glp-1 mutation of C. elegans and discover that the DNA region encoding the spatial control region (SCR) has been deleted. What will the GLP-1 protein expression pattern be in a four-cell embryo in mutant heterozygotes? In mutant homozygotes?

Assess the validity of Monod and Jacob’s remark that “anything found to be true of E. coli must also be true of Elephants.”