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Ch. 23 - Developmental Genetics
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All textbooksKlug 12th EditionCh. 23 - Developmental GeneticsProblem 18

Chapter 22, Problem 18

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?

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Hey, everyone. Let's take a look at this question together in Drosophila, Milano Gaster. The extra sex combs gene controls the development of sex combs and males. What happens when the extra sex combs gene is mutated in male Drosophila flies? Well, let's recall what we know about the importance of the extra sex combs gene. And what would happen if that gene is mutated in the male Drosophila flies. So we know that the extra sex comb gene is responsible for regulating the development of the sex combs in the male Drosophila flies. And when we have this mutated, that means that we have that reduction of development of sex combs, which means that we end up with either improper function or even an absence of the sex homes in the male Drosophila fly us, meaning that the number of the sex combs decreases. So, answer choice B is the correct answer because in the Drosophila flies, the extra sex combs gene controls the development of sex combs and males. And when we have this mutated extra sex comb gene, that means that we have a reduction of the development of the sex combs and we end up with an improper function or absence of sex combs entirely. So the number of sex combs decreases. So answer choice B is the correct answer. I hope you found this video to be helpful. Thank you and goodbye.
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The maternal-effect mutation bicoid (bcd) is recessive. In the absence of the bicoid protein product, embryogenesis is not completed. Consider a cross between a female heterozygous for the bicoid alleles (bcd⁺/bcd⁻) and a male homozygous for the mutation (bcd⁻/bcd⁻).

Predict the outcome (normal vs. failed embryogenesis) in the F₁ and F₂ generations of the cross described.

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Formation of germ cells in Drosophila and many other embryos is dependent on their position in the embryo and their exposure to localized cytoplasmic determinants. Nuclei exposed to cytoplasm in the posterior end of Drosophila eggs (the pole plasm) form cells that develop into germ cells under the direction of maternally derived components. R. Amikura et al. [(2001). Proc. Nat. Acad. Sci. (USA) 98:9133–9138] consistently found mitochondria-type ribosomes outside mitochondria in the germ plasma of Drosophila embryos and postulated that they are intimately related to germ-cell specification. If you were studying this phenomenon, what would you want to know about the activity of these ribosomes?
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One of the most interesting aspects of early development is the remodeling of the cell cycle from rapid cell divisions, apparently lacking G1 and G2 phases, to slower cell cycles with measurable G1 and G2 phases and checkpoints. During this remodeling, maternal mRNAs that specify cyclins are deadenylated, and zygotic genes are activated to produce cyclins. Audic et al. [(2001). Mol. and Cell. Biol. 21:1662–1671] suggest that deadenylation requires transcription of zygotic genes. Present a diagram that captures the significant features of these findings.

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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?

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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?

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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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