The curly hair gene does not fully dominate the straight hair gene, and an intermediate manifestation

The curly hair gene does not fully dominate the straight hair gene, and an intermediate manifestation of the trait is observed in heterozygotes – wavy hair. Determine what kind of children can be born in a marriage between a curly brunette, whose mother had blonde hair, and a blonde with straight hair. In a person, dark hair is a dominant feature.

Let’s designate the gene that determines the development of curly hair “A”, and the gene for straight hair – “a”. Wavy hair is the result of incomplete dominance, which means that the combination of the dominant and recessive genes in the genotype causes the development of a new trait – Aa.

Let’s designate the gene that causes the development of dark hair as B, then blonde hair will be caused by the gene b, which is homozygous – bb.

A curly haired brunette, based on the accepted designations, will be written as AABB or AABb. There is a clarifying circumstance in the problem:

the mother had blonde hair, so the man was AABb. It produces spermatozoa AB and Ab.

A blonde with straight hair – aab, her eggs – ab.

Children who may result from this marriage will have:

dark wavy hair (AaBb) – 50%;

light wavy hair (Aabb) – 50%.