Answer :
If one parakeet is heterozygous, that means it has one dominant gene and one recessive gene (Rr). If the other is homozygous for white feathers, then it has two recessive genes (rr). Crossing these two in a punnet square gives you 50%.
According to the Punnett square for this cross, what percentage of offspring is predicted to have blue feathers 50 per cent. Thus, option "B" is correct.
How, explain your answer briefly?
A single copy of a dominant allele is enough to be expressed, but recessive alleles need two copies to express. For that reason, the possible genotypes and phenotypes for feather colors are:
- BB: blue
- Bb: blue
- bb: white
The parakeet with blue feathers is heterozygous, so it the has both a dominant allele for blue feathers (B) and a recessive allele for white feathers (b) and the genotype is Bb. The other parakeet is homozygous for white feathers, so it has two b alleles and the genotype bb.
When individuals produce gametes, the alleles separate, so the heterozygous parakeet will produce the gametes B and b, and the homozygous parakeet will produce two b gametes.
The Punnett Square shows the possible combination of the gametes produced by the two parents, and therefore the genotypes of the offspring:
- Bb - blue feathers
- Bb - blue feathers
- bb - white feathers
- bb - white feathers
2 out of four individuals of the offering (50%) will have the genotype Bb and blue feathers.
Thus, option "B" is correct.
To learn more about Punnett square click here:
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