Q4. In NCERT’s skin-colour model, a person of genotype AABBCC has children with a person of genotype aabbcc. What is the children’s genotype, and what is their colour?
All the children are AaBbCc: 3 dominant and 3 recessive alleles, an intermediate colour (NCERT page 69).
Q5. A person of genotype AaBbCc has children with a person of genotype aabbcc. What fraction of the children would you expect to be aabbcc?
The aabbcc parent gives only abc. The AaBbCc parent gives abc with chance ½ × ½ × ½ = 1/8. So 1/8 of the children are expected to be aabbcc.
Q6. Assume four independently assorting loci, equal additive allele effects, and no environmental variation. How many phenotype classes can two parents heterozygous for all four give, and how many of 256 offspring are expected to fall in the middle class?
The children carry 0 to 8 dominant alleles: 9 classes. The middle class, 4 dominant alleles out of 8 places, has an expected frequency of 70/256; about 70 of 256 offspring, not a guaranteed count (our working with NCERT’s additive model, page 69).
Q7. Two people with genotype AaBbCc have 64 children (a thought experiment). About how many would you expect to have 4 or more dominant alleles?
15 + 6 + 1 = 22 of the 64, about a third.