The blue-eyed right-hander married the brown-eyed right-hander. They had two children – a brown-eyed

The blue-eyed right-hander married the brown-eyed right-hander. They had two children – a brown-eyed left-hander and a blue-eyed right-hander. From the second marriage of this man with another brown-eyed right-hander, 9 brown-eyed children were born, all are right-handed. What are the genotypes of all three parents? Which traits are dominant, which ones are recessive?

Since in the first marriage, two right-handed parents have a left-handed child, it should be concluded that the gene for right-handedness dominates over the gene for left-handedness.

Since in the second marriage all children of a blue-eyed man have brown eyes, it should be concluded that the brown-eyed gene dominates over the blue-eyed gene.

Let’s designate the gene that determines the priority of the right hand over the left in a person as K, then left-handedness will be determined by the gene designated as k.

Let’s designate the gene that determines the development of blue eyes in humans as m, then the gene for brown eyes will be M.

A left-handed child born in the first marriage for this trait is homozygous for the recessive gene – kk. Since he inherits the recessive genes k from both parents, it should be concluded that both parents are heterozygous for the leading hand.

Since one of the children born in the first marriage has blue eyes, and, therefore, has a genotype mm homozygous for the gene for blue eyes, his brown-eyed mother is heterozygous for eye color.

Thus, the woman from the first marriage has the diheterozygous genotype KkMm, and the blue-eyed right-handed man has Kkmm.

All children from marriage with a second woman have brown eyes and a right hand as the leading one.

Since the blue-eyed father transmits them only the recessive gene for blue eyes m, it should be concluded that the brown-eyed woman from the second marriage is homozygous for the dominant gene for brown eyes and transmits only the dominant gene M to the offspring, and all her brown-eyed children are thus heterozygous for eye color – Mm.

Despite the fact that half of the sperm produced by a man contain the recessive gene k, all children are right-handed, therefore, their mother is homozygous for the right dominant hand – KK and exclusively produces eggs with this dominant K gene. 50% of her children are homozygous KK, 50% – heterozygotes Kk, but all have the right hand as their dominant hand.

Answer: the male is heterozygous for the dominant hand and homozygous for eye color (Kkmm); the woman from the first marriage is diheterozygous (KkMm); woman from second marriage is dihomozygous for dominant genes (KKMM)