Answer: 50% of the offspring are predicted to have blue feathers.
Explanation:
<h3>Simple Dominance</h3>
I'm going to assume since the problem didn't say otherwise that we're working with simple dominance. This is usually the first kind of inheritance that we learn about in school.
For every gene, there are two alleles, a dominant allele (B), and a recessive allele (b). We represent these as a capital letter and a lower case letter. For this problem, let's use a 'B' for blue. There are three combinations that these can come in:
- BB - homozygous dominant
- Bb - heterozygous
- bb - homozygous recessive
If the alleles are the same, we say the organism is homozygous for the gene. If it has one of each, then the organism is heterozygous.
In simple dominance, if there's a dominant allele present (B), the organism will always show the dominant phenotype (in this case, blue feathers). So, the only offspring that can have white feathers are the ones with a bb genotype.
<h3>Punnett Square</h3>
A punnet square is a tool used by biologists to determine the probability of two organisms' offspring having certain genotypes. For this simple cross, where we have one gene with two alleles, we just need a 2x2 square. On either side of the square, we're going to put the two alleles of each parent. Then, we'll take each allele on top and add it to the boxes beneath it. Finally, take the alleles on the side and place them in the boxes to their right. I'll attach the completed square to my answer.
<h3>Interpreting the Results</h3>
Once the entire square is filled in, we'll see the following results:
2/4 offspring will have a heterozygous genotype (Bb) and therefore have blue feathers.
2/4 offspring will have a homozygous recessive genotype (bb) and have white feathers.
So, one-half, or 50%, of the parakeets' offspring will have blue feathers.
