A right-handed man whose mother was left-handed married a right-handed woman who

A right-handed man whose mother was left-handed married a right-handed woman who had three siblings, two of whom are left-handed. Determine the possible genotypes of the woman and the likelihood that the children born from this marriage will be left-handed.

Let’s designate the gene that determines the predominant ownership of the right hand by a person as K, then the gene that causes left-handedness will be designated as k.

The man’s mother, according to the condition, was left-handed. She had the kk genotype homozygous for the left-handed gene, because homozygosity is a necessary condition for the implementation of this trait in the phenotype. She could only pass on the recessive gene k to a man. Therefore, the right-handed man is heterozygous – Kk. It produces two types of sperm – K and k.

Two of the three female siblings also had genotypes homozygous for the recessive gene kk. They inherited recessive genes from both parents, which means that the woman’s parents were able to transmit both dominant and recessive genes to their offspring.

Consequently, the genotype of a right-handed woman can be both homo- and heterozygous.

Let’s consider both options.

Let the woman be homozygous for the dominant gene – KK. She produces the same type of eggs K. In a marriage with the man described above, offspring will appear, including the following options: heterozygous right-handed children (Kk) – 50%, homozygous right-handed children (KK) – 50%;

Let the woman be heterozygous – Kk. Like a man, she produces two types of germ cells – K and k. The offspring will include the following options: homozygous right-handed children (KK) – 25%, heterozygous right-handed children (Kk) – 50%, homozygous left-handed children (kk) – 25%.

Answer: if a woman is homozygous, then the probability of having a left-handed child is 0%; if the woman is heterozygous – 25%.