The color of plumage in hens is inherited by the type of incomplete dominance (black plumage dominates over white, an intermediate sign is colorful plumage). Variegated hens were crossed with variegated roosters. It is known that even before fertilization, 70% of gametes bearing the recessive allele and 30% of gametes bearing the dominant allele die. Determine the percentage of offspring with all possible phenotypes.
We introduce the notation of genes and indicate the phenotype of heterozygous individuals:
A – black plumage;
a – white plumage;
Aa – colorful plumage.
– Record the crossing of motley hens with motley cocks:
– The condition says that 30% of gametes carrying the dominant allele (A) die. So 70% of these gametes (or 0.7) are viable. Also, 70% of gametes bearing the recessive allele (a) die, therefore, 30% (or 0.3) of these gametes are involved in fertilization.
Given the ratio of viable gametes, the ratio of offspring with different phenotypes can be calculated. This is convenient to do by constructing a Pennet lattice:
Thus, the following ratio of descendants is observed: 49% with black plumage, 42% with colorful and 9% with white.
Answer: in the offspring, 49% are individuals with black plumage, 42% – with motley, 9% – with white.
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