Chapter 22, Problem 20
In Arabidopsis, flower development is controlled by sets of homeotic genes. How many classes of these genes are there, and what structures are formed by their individual and combined expression?
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A number of genes that control expression of Hox genes in Drosophila have been identified. One of these homozygous mutants is extra sex combs, where some of the head and all of the thorax and abdominal segments develop as the last abdominal segment. In other words, all affected segments develop as posterior segments. What does this phenotype tell you about which set of Hox genes is controlled by the extra sex combs gene?
The apterous gene in Drosophila encodes a protein required for wing patterning and growth. It is also known to function in nerve development, fertility, and viability. When human and mouse genes whose protein products closely resemble apterous were used to generate transgenic Drosophila [Rincon-Limas et al. (1999). Proc. Nat. Acad. Sci. (USA) 96:2165–2170], the apterous mutant phenotype was rescued. In addition, the whole-body expression patterns in the transgenic Drosophila were similar to normal apterous.
What is meant by the term rescued in this context?
The apterous gene in Drosophila encodes a protein required for wing patterning and growth. It is also known to function in nerve development, fertility, and viability. When human and mouse genes whose protein products closely resemble apterous were used to generate transgenic Drosophila [Rincon-Limas et al. (1999). Proc. Nat. Acad. Sci. (USA) 96:2165–2170], the apterous mutant phenotype was rescued. In addition, the whole-body expression patterns in the transgenic Drosophila were similar to normal apterous.
What do these results indicate about the molecular nature of development?
The floral homeotic genes of Arabidopsis belong to the MADS-box gene family, while in Drosophila, homeotic genes belong to the homeobox gene family. In both Arabidopsis and Drosophila, members of the Polycomb gene family control expression of these divergent homeotic genes. How do Polycomb genes control expression of two very different sets of homeotic genes?
Vulval development in C. elegans is dependent on the response of some of the central epidermal progenitor cells in the region of the developing vulva to a chemical signal from the gonad. Signaling from the gonad is blocked by action of the vulvaless mutant let-23 so that none of the central progenitor cells form vulval structures. In the vulvaless mutant, n300, the central progenitor cells do not form.
Which gene is likely to act earlier in the vulval developmental pathway?
Vulval development in C. elegans is dependent on the response of some of the central epidermal progenitor cells in the region of the developing vulva to a chemical signal from the gonad. Signaling from the gonad is blocked by action of the vulvaless mutant let-23 so that none of the central progenitor cells form vulval structures. In the vulvaless mutant, n300, the central progenitor cells do not form.
What phenotype (vulva formed or vulvaless) would you expect from the double mutant? Why?