Hemophilia is a recessive trait linked to the X chromosome. albinism is an autosomal recessive trait. one married couple, normal in both signs, gave birth to a child with both of these anomalies. what is the probability of a healthy child being born in this family?
Let’s designate the gene that causes hemophilia in humans as g, and the chromosome containing this gene as Xg. The chromosome with the gene for normal blood clotting will be designated XG.
Let’s designate the gene that causes the development of albinism as c, then the gene that causes the development of normal pigmentation will be designated as C.
A child with both anomalies has the Xg Ycc genotype. He is necessarily a boy, and inherits a hemophilia-neutral Y chromosome from his father. Theoretically, a girl with hemophilia can be born only from a father suffering from this pathology, having inherited Xg from him, and in this task the father is healthy by condition.
A born boy inherits a chromosome with the Xg coagulation pathology gene from a healthy mother, therefore, the mother is heterozygous for hemophilia.
Since the child is albino and homozygous for the albinism gene, and the parents have normal pigmentation, it should be concluded that both parents are heterozygous – Cc.
Thus, the mother is XG Xg Cc, she produces eggs – XG C, Xg c, XG c, Xg C.
Father – XG YСс, produces spermatozoa – XG С, Yс, XG С, YС.
The offspring will be represented by the following possible options:
healthy girls (XG XG CC, 2XG Xg CC, 2XG XG CC, XG Xg CC);
girls with albinism (XG XG cc, XG Xg cc);
healthy boys (2XG Y CC, XG Y CC);
boys with hemophilia and albinism (Xg Ycc);
boys with albinism (XG Ycc);
boys with hemophilia (2Xg Y CC, Xg Y CC).
Healthy boys (2XG Y Cc, XG Y CC) and healthy girls (XG XG CC, 2 XG Xg Cc, 2 XG XG Cc, XG Xg CC) – 9 genotypes out of 16, or 56.25%.
Answer: the probability of having a healthy child for this couple is 56.25%.