Question

1. In Drosophilia, females are XX, while males are XY. Yellow bodies are determined by an X-linked recessive mutation X^b, while the dominant wild-type allele X^B produces brown bodies. A heterozygous female is crossed with a brown bodied male to produce the F1 generation.

^{a) Among the F1 generation, what genotypes and phenotypes would be expected among the progeny, and in what proportion?}

^{b) from the F1 generation, males and females are mated at random. What genotypes and phenotypes would be expected among the progeny in the F2, and in what proportions?}

Answer 1

Given, alleles for body color Allele XB dominant, produces the phenotype 'brown body color Allele Xb - recessive, produces the phenotype yellow body color Also, the gene for body color is X- lined The female is XX, and male is XY For this pair of dominant and recessive allele The genoypes producing dominant phenotype (brown body color)-XBXBXBXbXBY The genoypes producing recessive phenotype (yellow body color)-XKXb XbY Now genotype of the female parent (heterozygous)-XB Xb :Gametes formed Xp, Xb genotype of the male parent (brown body color) XB Y ;Gametes formed-XB, Y XBXB Random mating of F1 progeny- Хуу Xb Genotyoic ratio (GR) PR, BF B, M-11 PR. B, F B, M1:1 Phenotypic ratio (PR) Brown, female Brown, male: White male 2:1 Xp For F2- B- brown. Y-yellow M- male, F- female GR PR, B.F B, M Y, M2PR B.F: B,Y:B, M: B, Y 1:1:1:1 Overall genotypic ratio in F2 (include add the 4 crosses)- Overall phenotypic ratio in F2 (include add the 4 crosses) Brown, female yellow female Brown male yellow male 7: 1: 6:2