In the family, one child is right-handed and the other is left-handed, determine the genotypes if right-handedness

In the family, one child is right-handed and the other is left-handed, determine the genotypes if right-handedness is the dominant feature and left-handedness is recessive.

Let’s designate the gene that causes the development of right-handedness as B, and the gene that leads to the development in a person of the ability to predominantly use the left hand as b.

A left-handed child is homozygous for the gene for left-handedness of genotypes bb. It is formed as a result of inheritance from each of the parents for the recessive gene b. Consequently, both parents have such a gene in their genotypes. Since the second child is right-handed, that is, has either the BB or Bb genotype, therefore, the parents are able to transmit the dominant B gene as well.

Possible variants of parental genotypes: Bb and Bb, Bb and bb. Let’s consider both options.

Let both parents be heterozygous – Bb. They are right-handed and produce germ cells B and b. Children will be presented with options: right-handers (BB, Bb) – 75% and left-handers (bb) – 25%;

Let one of the parents be a heterozygous right-hander Bb (gametes – B and b), and the other is homozygous for the recessive gene left-handed cc (gametes b). Possible offspring options: heterozygous right-handed children (Bb) – 50% and left-handed children homozygous for the recessive gene (bb) – 50%.