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5.8 Sex Determination — Test 1
Q1. Sex determination in Drosophila is based on the ratio of the number of X chromosomes to:✓ The number of sets of autosomes (the X:A ratio)
Q2. Because the Y chromosome plays no role in Drosophila sex determination, an XO Drosophila develops as a:✓ Sterile male
Q3. In Drosophila, a high X:A ratio activates which feminizing switch gene?✓ Sex-lethal (Sxl)
Q4. The Drosophila Sex-lethal (Sxl) gene regulates sex at which level?✓ Post-transcriptional (alternative splicing)
Q5. In Drosophila, the Sxl product controls sex by regulating the splicing of:✓ transformer (tra) RNA, which then regulates doublesex
Q6. A Drosophila embryo in which Sex-lethal can only undergo default (male) splicing develops as a:✓ Male
Q7. In mammals, sex is determined primarily by:✓ The presence of the Y chromosome (SRY gene)
Q8. In Drosophila XO are male and XXY are female, but in humans XO are female and XXY are male. This contrast shows that:✓ Human sex depends on the Y, while Drosophila sex depends on the X:A ratio
Q9. In C. elegans, transferring an X segment into an XO male can restore female (hermaphrodite) character, showing sex is set by:✓ The X-to-autosome (X/A) ratio
Q10. In mammals, the bipotential genital ridge becomes a testis when which gene is activated?✓ Sox9 (downstream of SRY)
Q11. In mammalian ovary determination, the key pathway involves Wnt4, R-spondin1 and:✓ beta-catenin accumulation
Q12. Which statement about the bipotential mammalian gonad is INCORRECT?✓ R-spondin1 promotes the testis pathway
Q13. Temperature-dependent sex determination (TSD), where incubation temperature sets the sex, is found in:✓ Many reptiles such as crocodilians and turtles
Q14. A Drosophila with the chromosome complement XXXXY/AA (four X, two sets of autosomes) would be a:✓ Metafemale (superfemale)
Q15. The fact that environmental temperature can set sex in some reptiles, while chromosomes set it in mammals, shows that sex determination:✓ Uses different mechanisms in different animal groups
Q16. The mammalian SRY gene is located on the:✓ Y chromosome
Q17. In mammals, the SRY protein initiates male development by switching on:✓ Sox9 (driving Sertoli-cell and testis formation)
5.8 Sex Determination — Test 2
Q18. An XY human individual with a non-functional androgen receptor develops as phenotypically female. This condition is:✓ Androgen insensitivity syndrome
Q19. A human with XXY chromosomes has which condition?✓ Klinefelter syndrome (male)
Q20. A human with a single X (XO) has which condition?✓ Turner syndrome (female)
Q21. Dosage compensation in mammals equalises X-gene expression between sexes by:✓ Inactivating one X chromosome in females (forming a Barr body)
Q22. In Drosophila, dosage compensation works differently — by:✓ Doubling the expression of the single X in males
Q23. In Drosophila, the master switch gene Sxl is ON in females and controls dosage compensation by:✓ Preventing the male-specific up-regulation of the X
Q24. The doublesex (dsx) gene at the bottom of the Drosophila cascade is notable because it:✓ Produces different proteins in males and females by alternative splicing
Q25. In temperature-dependent sex determination, the temperature acts during a specific window called the:✓ Thermosensitive period
Q26. In many turtles with TSD, warmer incubation temperatures tend to produce:✓ More females
Q27. The gonad before sex determination is described as 'bipotential' because it:✓ Can develop into either a testis or an ovary
Q28. In mammals, the male and female gonad pathways are mutually antagonistic, meaning:✓ Each represses the other so the gonad commits fully to one fate
Q29. Anti-Mullerian hormone (AMH), secreted by the developing testis, causes:✓ Regression of the Mullerian (female) ducts
Q30. Honeybee males (drones) develop from unfertilised eggs and are haploid, an example of:✓ Haplodiploid sex determination
Q31. The fact that mammals use SRY, flies use the X:A ratio, bees use ploidy and some reptiles use temperature shows that sex determination is:✓ Evolutionarily diverse, with many different mechanisms
Q32. The gene family Dmrt/doublesex is interesting because it functions in sexual development across:✓ Very distantly related animals (flies to mammals)
Q33. In birds, the sex chromosome system is ZW, where the female is:✓ The heterogametic sex (ZW)
Q34. Overall, sex determination illustrates the principle that a binary developmental choice can be controlled by:✓ A switch gene at the top of a regulatory cascade