7. How does sex determination in Drosophila differ from sex determination in humans? 9. What characteristics are exhibited by an X-linked trait? 11. What characteristics are exhibited by a Y-linked trait? 12. Explain why tortoiseshell cats are almost always female and why they have a patchy distribution of orange and black fur. 13. What is a Barr body? How is it related to the Lyon hypothesis? 15. What is the sexual phenotype of fruit flies having the following chromosomes? Sex chromosomes | Autosomal chromosomes | Sexual phenotype c. XO | All normal | e. XYY | All normal | g. XXX | All normal | i. XXX | Four haploid sets | 17. For each of the following chromosome complements, what is the phenotypic sex of a person who has c. XO with a copy of the SRY gene on an autosomal chromosome? d. XXY with the SRY gene deleted? e. XXYY with one copy of the SRY gene deleted 35. Red-green color blindness is an X-linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. If Bill and Martha marry, what phenotypes and proportions of children can they produce?
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Sex determination in Drosophila differs from sex determination in humans as follows: In Drosophila, sex is determined by the ratio of X chromosomes to autosomes, whereas in humans, it is determined by the presence or absence of the Y chromosome. In Drosophila, XX Show more…
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In Drosophila, a cross was made between a females expressing the three X-linked recessive traits scute bristles (b), sable body (s), and vermillion eyes (v) – and a wild-type male. In the F1, all females were wild-type in phenotype, and all males expressed all three mutant traits. The cross was carried to the F2 generation, and 1000 offspring were counted with the results shown on the table. a) Indicate the genotypes of both individuals of the parental generation and of the two different types of F1 offspring. This can best be done by drawing the sex chromosomes of each individual indicating gene order and which alleles are present on each chromosome. b) Determine the map distances between the three genes.
Katlin K.
In the sex determination system found in Drosophila, what does the Sxl (Sex lethal) gene do? A. When expressed (On) initiates female development. B. When expressed (On) initiates male development. C. Is lethal if expressed. D. Blocks the expression of sisterless genes. E. Counts the number of X chromosomes. F. Counts the number of autosomes. Which statement is true about the pseudo-autosomal region (PAR)? A. The PAR is a region on the Y but also on an autosome. B. The PAR is never involved in recombination. C. The PAR carries sex determining genes. D. The PAR is found only on the Y chromosome in mammals. Which is true about this statement. Trisomics occur and survive to adulthood in humans. A. Yes but Downs syndrome is the only example. B. Yes but 3N = 69 is unbalanced and causes major developmental problems. C. Yes but none of the other statements is correct. D. Never. E. Yes but only for 2N = 47 (+X).
Sri K.
In Drosophila, a cross was made between females expressing the three X-linked recessive traits, scute bristles $(s c),$ sable body $(s)$ and vermilion eyes ( $v$ ), and wild-type males. All females were wild type in the $F_{1},$ while all males expressed all three mutant traits. The cross was carried to the $\mathrm{F}_{2}$ generation and 1000 offspring were counted, with the results shown in the following table. No determination of sex was made in the $\mathrm{F}_{2}$ data. (a) Using proper nomenclature, determine the genotypes of the $P_{1}$ and $F_{1}$ parents. (b) Determine the sequence of the three genes and the map distance between them. (c) Are there more or fewer double crossovers than expected? (d) Calculate the coefficient of coincidence; does this represent positive or negative interference?
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