Question

Two mothers give birth to sons at the same time at a busy urban hospital. The son of mother 1 is afflicted with hemophilia, a disease caused by an X-linked recessive allele. Neither parent has the disease. Mother 2 has a normal son, despite the fact that the father has hemophilia. Several years later, couple 1 sues the hospital, claiming that these two newborns were swapped in the nursery following their birth. As a genetic counselor, you are called to testify. What information can you provide the jury concerning the allegation?

Accepted Answer

Step 1: Understand the inheritance pattern of hemophilia, which is an X-linked recessive disorder. This means the gene causing hemophilia is located on the X chromosome, and males (XY) who inherit the affected X chromosome will express the disease because they have only one X chromosome. Step 2: Analyze the genetic status of the first family. Since the son of mother 1 has hemophilia but neither parent shows the disease, the mother must be a carrier (X^H X^h) and the father must have a normal X chromosome (X^H Y). The son inherits the affected X chromosome (X^h) from the mother and a Y chromosome from the father, resulting in hemophilia. Step 3: Analyze the second family. The father has hemophilia (X^h Y), so he can only pass the affected X chromosome to his daughters and the Y chromosome to his sons. Since mother 2 has a normal son, this son must have inherited the Y chromosome from the father and a normal X chromosome (X^H) from the mother, meaning the mother is not a carrier. Step 4: Use this information to assess the claim of swapped babies. The son with hemophilia must have inherited the affected X chromosome from his mother, so the mother of the hemophiliac son must be a carrier. The normal son born to the father with hemophilia must have inherited a normal X chromosome from his mother, who is not a carrier. This genetic evidence supports that the babies were not swapped. Step 5: Summarize for the jury that the genetic patterns of X-linked inheritance and the presence or absence of carrier status in the mothers provide strong evidence against the claim that the babies were swapped in the nursery.

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Concetti chiave

X-linked Recessive Inheritance

Genetic Probability and Carrier Status

Paternity and Maternity Testing Using Genetic Markers