A dark-haired, big-eyed woman (dominant), heterozygous for both traits, marries a fair-haired, big-eyed man whose mother had small eyes. Phenotypes and genotypes of people.
Let’s designate the gene that causes the development of dark hair in humans as B, then the gene for light hair will be b.
Let’s designate the gene that causes the development of large eyes as C, then the gene for small eyes will be c.
The dark-haired, big-eyed mother is diheterozygous by the statement of the problem. Let’s write it down as ВbСс. Her body produces four types of eggs: bc, BC, bc and bC.
A fair-haired man with big eyes inherits the gene for small eyes from his mother, because she could not pass on another gene to him. Consequently, a man is heterozygous for the eye size gene. Since he has fair hair, he is homozygous for the hair color gene, otherwise this trait could not be realized in the phenotype. Let’s write the man as bbСс. It produces two types of sperm: bC and bc.
The offspring possible for a given married couple will look like this:
blonde children with big eyes (2bbСс, bbСС);
dark-haired children with big eyes (BbCC, 2BbCc);
blonde children with small eyes (bbcc);
dark-haired children with small eyes (Bbcc).