A couple has just learned that their daughter has hemophilia. They already have a son who does not have the disease. What are the genotypes of the couple? Explain your reasoning.
A couple has just learned that their daughter has hemophilia. They already have a son who does not have the disease. What are the genotypes of the couple? Explain your reasoning
To determine the genotypes of the couple, we need to understand the inheritance pattern of hemophilia. Hemophilia is an X-linked recessive disorder, meaning it is carried on the X chromosome.
Let's denote the X chromosome as X and the Y chromosome as Y. Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
In the given scenario, we know that the couple has a daughter with hemophilia and a son without the disease. From this information, we can infer the possible genotypes for the couple.
A male child can only inherit the X chromosome from the mother and the Y chromosome from the father. Since the son does not have hemophilia, it means he has inherited a normal copy of the X chromosome from his mother.
Since the daughter has hemophilia, she must have received the X chromosome carrying the hemophilia gene from both of her parents.
Based on this information, we can deduce the following possibilities for the genotypes of the couple:
1. The mother is a carrier of hemophilia (X(h)X) and the father does not carry the hemophilia gene (XY). In this case, the son has a normal X chromosome and does not have hemophilia, while the daughter has one normal X chromosome and one X chromosome with the hemophilia gene, leading to the development of hemophilia.
2. The father is a carrier of hemophilia (X(h)Y) and the mother does not carry the hemophilia gene (XX). In this case, the son receives the normal X chromosome from the mother and the Y chromosome from the father, resulting in no hemophilia. The daughter receives the X chromosome with the hemophilia gene from the father and the normal X chromosome from the mother, leading to the development of hemophilia.
In summary, the most likely genotypes of the couple are:
- Mother: X(h)X (carrier of hemophilia)
- Father: XY (non-carrier of hemophilia)