100 black guinea pigs were crossed to white guinea pigs; the offspring were then
ID: 37409 • Letter: 1
Question
100 black guinea pigs were crossed to white guinea pigs; the offspring were then crossed to yield an f2 generation. In 85 of the crosses, the f1 individuals were all black and in the f2 generation that followed black and white guinea pigs appeared in a 3 black: 1 white ratio. In the other 15 crosses, half of the f1 animals were black and half we're white. Please provide a genetic explanation of the phenomena.And what offspring ratios would you expect from crossing the f1 offspring of the guinea pigs from the 15 exceptional crosses? 100 black guinea pigs were crossed to white guinea pigs; the offspring were then crossed to yield an f2 generation. In 85 of the crosses, the f1 individuals were all black and in the f2 generation that followed black and white guinea pigs appeared in a 3 black: 1 white ratio. In the other 15 crosses, half of the f1 animals were black and half we're white. Please provide a genetic explanation of the phenomena.
And what offspring ratios would you expect from crossing the f1 offspring of the guinea pigs from the 15 exceptional crosses?
And what offspring ratios would you expect from crossing the f1 offspring of the guinea pigs from the 15 exceptional crosses?
Explanation / Answer
Here the gene allele for black color (B) is domint over white (b).
For the first 85 crosses:
The black guinea pigs were homozygous (BB) for black color whereas white guinea pigs were homozygous for white (bb). Thus they produced all black (Bb) in F1 generation. When these F1 offsprings were crossed with each other, they produced Black : White in 3 : 1 ratio although the genotype for these F2 offsprings was in the ratio of 1 : 2 : 1 (BB : Bb : bb).
For the later 15 crosses:
The genotype of black parents was Bb i.e. heterozygous for blak color. Therefore, they produced Black and white in the ratio of 1 : 1 (Bb : bb). Later when these black and white F1 offsprings were again crossed with each other, they would again produce the same result i.e. black and white in the ratio of 1 : 1 (Bb : bb).
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