Problems
1. The presence of three types of sex chromosomes allows different sex ratios to be obtained in various crosses of the platy. Find out the sex ratios for the following crosses. a) XX × XY b) WY × YY c) WX × YY d) WX × XY e) WY × XY f) XX × YY 2. Find out the sex ratio of F1 hybrid progeny from a cross of a female Oreochromis mossambicus and a male O. hornorum?
3. In the case of medaka, Oryzias latipes the mechanism of sex determination is XY system. Find out the sex ratio among the progeny produced from the following crosses. a) XX × XX (T) b) XY (T) × XY c) XY (T) × YY (from the second cross) d) YY (T) × YY (from the second cross) e) XX × YY (from the second cross) 4. Find out the genotypic and phenotypic ratio for the mating of a female grey and maculatus male guppy?
5. Find out the sex ratio for the progeny of the following crosses produced in guppy ? a) caudalis ♀ × caudalis ♂ b) transparent tailed ♀ × caudalis ♂ c) caudalis ♀ × transparent tailed ♂
6. In the Lebistes reticulates there is a black spot on the dorsal fin. In crosses of black spot males with normal females half the progeny have the black spot and other half do not. Black spot occurs only in males. Moreover, black spot does not occur in males unless the father expressed the trait. Result a diagrammatic explanation of these results showing which is the homogametic sex. Show what would be expected if the gene controlling black spot were located on the alternative sex chromosome to that you have postulated. 7. In platy, a cross between a `Nigra’ female (N) and a lightly pigmented male (W) produced ‘Nigra’ sons and ‘white’ daughters which, in an F2, produced approximately equal frequencies of ‘Nigra’ and ‘white’ individuals of each sex. Interpret the results of the above cross? |