In Aplocheilus, females are homogametic – XX, and males are heterogametic – XY. The Y chromosome, just like the X chromosome, contains alleles of genes. The fish are normally brown in color, determined by the B allele; blue color – b. The Y chromosome always contains the B allele and never the b allele. Consequently, males are never blue. What F1 and F2 offspring should be expected from crossing a blue female with a homozygous brown male?
From crossing a blue female with a homozygous brown male in F1, brown females and brown males can be expected in a 1: 1 ratio; in F2 – brown males, brown females and blue females in a ratio of 2: 1: 1.
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