A woman with protruding ears married a man with normal ears, and from this marriage two daughters
A woman with protruding ears married a man with normal ears, and from this marriage two daughters were born, one of whom had protruding ears. The youngest daughter with normal ears married a man with the same ears. They had two sons, one of whom has protruding ears. Determine the nature of the inheritance of the trait (dominant or recessive, linked or not linked to the sex), the genotypes of the parents and children of the first and second generations.
Since protruding ears appear in one of the sons of a man and a woman with normal ears, it should be concluded that the gene for protruding ears is recessive. Let’s denote it as k. Then the gene for normal-shaped ears will be designated K.
The gene of the trait in question is not associated with sex, since, being associated with the Y – chromosome, it would necessarily be transmitted only through the male line, and in this task, protruding ears are also found in women. Being bound to the X chromosome, it could not cause protruding ears in the daughter of a man with normal ears.
A child with protruding ears has a homozygous genotype kk, because a recessive trait can be realized phenotypically only if the genotype of its owner is homozygous.
Therefore, both parents are heterozygous for the ear shape gene – Kk. They produce two types of germ cells – K and k.
Their possible offspring are represented by the following options:
children with a normal shape of the auricle (KK, Kk) – 75%;
children with protruding ears (kk) – 25%.