Question

Two mothers give birth to sons at the same time at a busy urban hospital. The son of mother 1 has hemophilia, a disease caused by an X-linked recessive allele. Neither parent has the disease. Mother 2 has a son without hemophilia, 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?

Short answer

In conclusion, the inheritance patterns of hemophilia in both the couple's situations do not support the allegation that the newborns were swapped in the hospital. Couple 1's son has a 25% chance of having hemophilia, while Couple 2's son has a 100% chance of not having hemophilia. These patterns indicate that the given scenarios are possible without involving a newborn swap.

Step-by-step solution

Understanding Hemophilia Inheritance

Hemophilia is a sex-linked recessive disease, which means that it is carried on the X chromosome. Males have one X and one Y chromosome (XY), and females have two X chromosomes (XX). A male offspring receives the X chromosome from his mother and the Y chromosome from his father, while a female offspring receives an X chromosome from both parents. If a male has the hemophilia allele on his X chromosome, he will have the disease since there is no corresponding allele on the Y chromosome to mask its effect. In contrast, females can be carriers of the disease without manifesting any symptoms if they have only one X chromosome with the disease allele.

Analyzing the First Couple's Situation

Couple 1 has a son with hemophilia, and neither parent has the disease. For the son to have hemophilia, he must have received the X chromosome with the hemophilia allele from his mother, who must be a carrier (XHXh). The father has a normal X chromosome (XHY). The inheritance pattern can be illustrated as follows: Mother (XHXh) x Father (XHY) - XHXH (daughter, non-carrier) - XHXh (daughter, carrier) - XHY (son, non-hemophiliac) - XhY (son, hemophiliac) In this case, there is a 25% chance of having a son with hemophilia, making their situation possible without any evidence of a newborn swap.

Analyzing the Second Couple's Situation

Couple 2 has a son without hemophilia, even though the father has the disease. The father has an X chromosome with the hemophilia allele (XhY) and the mother has two normal X chromosomes (XHXH). The inheritance pattern can be illustrated as follows: Mother (XHXH) x Father (XhY) - XHXh (daughter, carrier) - XHY (son, non-hemophiliac) In this case, there is a 100% chance of having a son without hemophilia and a 100% chance of having a daughter who is a carrier, which also makes this situation possible without evidence of a newborn swap.

Conclusion

Based on the information provided and the inheritance patterns of hemophilia, both the first and second couple's situations are possible without any indication of a newborn swap. It is essential to inform the jury about these inheritance patterns in this case, which do not support the allegation that the newborns were switched in the hospital.