Recall from Chapter 17 that in Drosophila, sex determination depends on the number of X chromosomes: XX flies are female, and XY flies are male. The elaboration of female morphology depends on a cascade of gene regulation initiated by the expression of the Sxl gene in XX embryos (Fig. 17.35 and Fig. 17.36). Sxl causes splicing of the tra gene transcript in a manner that allows translation of Tra protein. Tra protein in turn causes female-specific splicing of the dsx mRNA and expression of Dsx-F protein, a transcription factor. Dsx-F activates the transcription of female morphology genes and represses male morphology gene expression. The ix gene product, Ix protein, is required for Dsx-F to repress the expression of male morphology genes.
a. | Drosophila sex determination is a switch/regulation pathway. Define the signal and the switch in this pathway. In what cells is the switch ON? OFF? |
b. | Describe the tra- and ix- mutant |
c. | Predict the mutant phenotype of tra- ix- null double mutants. Which mutation would you expect to be epistatic? |
d. | In the two examples discussed previously concerning epistasis analysis in the study of eye development-sev- and RasG12V described in the text, and sev- and yan- in Problem 23-the epistatic mutation defined the downstream gene in the pathway. Can you explain why that is not the case in this example for the sex determination pathway? |
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Genetics: From Genes to Genomes
- Explain the Drosophila genetics tool for gene expression known as the UAS-GAL4 systemarrow_forwardBriefly explain how the Dorsal protein is redistributed in the formation of the Drosophila embryo and how this redistribution helps to establish the dorsal–ventral axis of the fruit fly.arrow_forwardExplain how the Sxl promoter “counts” the number of Xchromosomes in Drosophila.arrow_forward
- 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?arrow_forwardDiscuss the morphological differences between the parasegments and segments of Drosophila. Discuss the evidence, providing specific examples, that suggests the parasegments of the embryo are the subdivisions for the organization of gene expression.arrow_forwardA Drosophila egg that is bed lbcd may develop normally, but the adult fruit fly will not be able to produce viable offspring. How is this possible? The mother can provide the bcd mRNA required for normal development, but the adult bcd /bcd female fly cannot make its own bcd mRNA. The Hox genes in the egg play a redundant role to bcd during development in a bcd / bcd egg, but reproduction requires bcd. Drosophila sperm contains the functional bcd gene product required for normal development, but the adult sex cells will not be able to produce the functional product. The nanos gene product functionally compensates for lack of bcd expression in the developing fly but not in its offspring.arrow_forward
- Explain what a morphogen is, and describe how it exerts its effects. What do you expect will happen when a morphogen is expressed in the wrong place in an embryo? List five examples of morphogens that function in Drosophila.arrow_forwardExplain about how X chromosome inactivation takes place in mammals at the chromosomal and molecular level. B. What genes are involved in inactivating a human X chromosome? . C. What role does X chromosome-specific inactivating transcript --XIST-- non coding RNA play in the inactivation of the human X chromosome.arrow_forwardDescribe the expression pattern of the Drosophila geneeve in the early embryo.arrow_forward
- Describe the relationship between homeotic genes in Drosophila and in mice.arrow_forwardSex Determination A .Compare sex determination in humans (what genetically and biochemically determines male vs female) and compare this to sex determination in Drosophila fruit flies what genetically and biochemically determines male vs female in fruit flies). B. What roles do the genes for a) sisterless, b) sex lethal (sxl) , tra (transformer gene) and dsx-f (double sex) play in Drosophila sex determinationarrow_forwardExplain how alternative splicing affects sex determination in Drosophila.arrow_forward
- Biology: The Dynamic Science (MindTap Course List)BiologyISBN:9781305389892Author:Peter J. Russell, Paul E. Hertz, Beverly McMillanPublisher:Cengage Learning