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?

Short answer

Answer: Yes, it is plausible that the newborns were swapped at birth based on the genetic information provided, but additional genetic testing would be needed to confirm the true parentage of the children.

Step-by-step solution

Understand the genetics of hemophilia

Hemophilia is a genetic disorder caused by a mutation in a gene on the X chromosome. It is an X-linked recessive disease, meaning that it predominantly affects males who have inherited one affected X chromosome from their carrier mother. Females can also be affected if they inherit the affected X chromosome from both their mother and their father, but this is very rare.

Identify the parents' genotypes

In order to determine if the newborns could have been swapped at birth, we first need to know the genotypes of the parents: Couple 1: Mother 1: Normal (likely carrier of hemophilia) => X^HX^h (X^H - normal X chromosome, X^h - X chromosome carrying hemophilia) Father 1: Normal => X^HY (Y chromosome, since he is a male) Couple 2: Mother 2: Normal => X^HX^H Father 2: Hemophilia => X^hY

Identify the possible offspring genotypes

Next, we will predict the possible genotypes of the offspring from each couple using a Punnett square. Offspring of Couple 1: The possible genotypes are X^HX^H (normal), X^HX^h (normal, carrier), X^HY (normal), and X^hY (hemophilia) Offspring of Couple 2: The possible genotypes are X^HX^h (normal, carrier), X^HY (normal), X^hX^h (hemophilia, female), and X^hY (hemophilia)

Determine if the claim is plausible

Now, let's analyze the results. Couple 1 claims that their son, who has hemophilia, was swapped with the son of couple 2, who does not have hemophilia. Considering that the son of couple 1 does have a genotype that could lead to hemophilia (X^hY), it is possible that they are indeed the biological parents. The son with hemophilia from couple 2 could also be their biological son, as that genotype is also plausible in offspring from couple 2 (X^hY). Similarly, the son without hemophilia being the biological child of couple 2 is also a possibility (X^HY). Based on this genetic analysis, it can be concluded that the claim of the newborns being swapped at birth is plausible but not definitive. Additional genetic testing would be needed to provide more compelling evidence and confirm the true parentage of these children.

Key concepts

X-linked Recessive

X-linked recessive conditions are genetic disorders that are carried on the X chromosome. This type of inheritance affects males, who have one X and one Y chromosome. They are more susceptible because they have only one X chromosome. This means if that X chromosome carries the recessive allele with a disorder, they will express the condition as they lack another X chromosome that may carry a normal allele.

Females have two X chromosomes and thus need to inherit two recessive alleles to express the disorder, making it much rarer for them. They can be carriers if they have one normal allele and one allele for the disease. In the context of hemophilia, a mother who is a carrier may pass the affected allele to her son, leading him to display symptoms of hemophilia if he inherits the X chromosome carrying the disorder. A carrier mother might have a genotype of X^HXh, while a normal father might have a genotype of X^HY.

Hemophilia Inheritance

Hemophilia is a well-known X-linked recessive disorder that affects blood clotting. In this condition, affected individuals, often males, bleed longer after injuries since their blood cannot clot properly due to a lack of necessary proteins in the bloodstream.

The inheritance follows typical X-linked recessive patterns:

• If the mother is a carrier (X^HXh) and the father is normal (X^HY), possible combinations for their children include normal daughters (X^HXH), carrier daughters (X^HXh), normal sons (X^HY), and affected sons (X^hY).
• If the father has hemophilia (X^hY), he cannot pass on a Y chromosome that carries the disorder to his sons, but he can pass the affected X chromosome to his daughters, potentially making them carriers.

Understanding these patterns helps in analyzing claims of swapped babies, as it allows genetic counselors to determine the likelihood of particular genotypes based on the described inheritance scenarios.

Punnett Square Analysis

A Punnett square is a simple tool used in genetics to predict and visualize the possible genotypes of offspring from parental genotypes. By placing the alleles of each parent on separate axes, the possible combinations for the offspring can be calculated.

The columns in a Punnett square typically represent one parent's alleles, while the rows represent the other parent's alleles. By filling in each cell of the grid, different possible genotypes for the children of these parents are displayed.

• For Couple 1, where the mother may be a carrier (X^HXh) and the father is normal (X^HY), the possible genotypes include boys with normal blood clotting (X^HY) or with hemophilia (X^hY).
• For Couple 2, with a normal mother (X^HXH) and affected father (X^hY), possible genotypes include girls who are carriers (X^HXh) and normal boys (X^HY).

This analysis is crucial for determining the genetic possibilities of offspring, thus illustrating the likelihood of any claims, such as baby swapping, being accurate. Proper utilization of the Punnett square provides clarity in understanding potential outcomes in genetic inheritance.