Question

In humans, the disease known as hemophilia is inherited as an \(\mathrm{X}\) -linked recessive trait. Sally and Sam, both of whom are normal, marry, and they have three children: (1) Saul, a hemophiliac, who marries a normal woman and has a daughter, Sarah, who is normal; (2) a normal daughter, Sheryl, who marries a normal man and has a son, Solomon, who is a hemophiliac; and (3) Shirley, also normal, who marries and has six normal sons. Using the letters \(\mathrm{H}\) and \(\mathrm{h}\) for the normal and hemophilia genes, respectively, and \(\nearrow\) to represent the \(\mathrm{Y}\) chromosome, determine the genotypes of Sally, Sam, Saul, Sarah, Sheryl, Solomon and Shirley.

Short answer

The genotypes of the family members are as follows: - Sally: \(X^HX^h\) - Sam: \(X^HY\) - Saul: \(X^hY\) - Sarah: \(X^HX^h\) - Sheryl: \(X^HX^h\) - Solomon: \(X^hY\) - Shirley: \(X^HX^H\)

Step-by-step solution

Write down the given genotypes

We are given the following information: \(H\) represents the normal allele (dominant), and \(h\) represents the hemophilia allele (recessive). Sally and Sam are normal and married, and they have three children (Saul, Sheryl, and Shirley). Since hemophilia is X-linked, men have one X chromosome with the gene for hemophilia or normal blood clotting (\(X^H \) or \(X^h\)) and one Y chromosome (which doesn't carry the blood clotting gene), while women have two X chromosomes with the gene for hemophilia or normal blood clotting (\( X^HX^H\),\(X^HX^h\), or \(X^hX^h\)).

Analyze the genotypes of Sally and Sam

Since both Sally and Sam are normal, we know that their genotypes must contain at least one dominant (\(H\)) allele. Sally can have one of the following genotypes: \(X^HX^H\), or \(X^HX^h\). Sam can have only one genotype since he has no X chromosome with a hemophilia allele: \(X^HY\).

Analyze the genotypes of Saul, Sarah, Sheryl, and Solomon

Saul is a hemophiliac (affected) male, so his genotype must be \(X^hY\). Saul marries a normal woman, indicating that she has at least one dominant (\(H\)) allele. Their daughter Sarah is normal, which means she inherited the dominant (\(H\)) allele from her mother. Since her father was a hemophiliac, she must have inherited the hemophilia allele \(h\) from him. Therefore, Sarah's genotype is \(X^HX^h\). Sheryl is a normal daughter, which means her genotype must be either \(X^HX^H\) or \(X^HX^h\). She marries a normal man, so his genotype must be \(X^HY\). Their son Solomon is a hemophiliac, which indicates that Sheryl must have the genotype \(X^HX^h\) for Solomon to inherit the hemophilia allele from her. Solomon's genotype will be \(X^hY\).

Analyze the genotypes of Shirley

Shirley is normal, so her genotype has to be either \(X^HX^H\) or \(X^HX^h\). She marries a man and has six normal sons. Since neither Shirley nor her husband is hemophiliac, the only way all of their sons can be normal is if Shirley has the genotype \(X^HX^H\).

Determine Sally's genotype

Since Saul received the hemophilia allele from Sally, we can now conclude that Sally has the genotype \(X^HX^h\). #Final Results# - Sally: \(X^HX^h\) - Sam: \(X^HY\) - Saul: \(X^hY\) - Sarah: \(X^HX^h\) - Sheryl: \(X^HX^h\) - Solomon: \(X^hY\) - Shirley: \(X^HX^H\)

Key concepts

Hemophilia and Genetics

Hemophilia is a genetic disorder that impacts the blood's ability to clot normally. This means that individuals with hemophilia are at risk for excessive bleeding even from minor injuries. The condition is typically inherited as an X-linked recessive trait, specifically meaning the gene causing hemophilia is located on the X chromosome. Everyone has two sex chromosomes; females usually have two X chromosomes (XX), while males have one X and one Y chromosome (XY). For X-linked conditions, the presence of just one affected allele can result in the disorder if you have only one X chromosome (like males). Females, having two X chromosomes, would need to have two affected alleles to fully exhibit symptoms of hemophilia. This is why males are more commonly affected by X-linked recessive disorders like hemophilia.

Understanding Recessive Genetic Traits

A recessive genetic trait is one that typically does not manifest unless two copies of the recessive allele are present. X-linked recessive traits, like hemophilia, behave slightly differently because of the distribution of X chromosomes in males and females.

• Females with one affected X chromosome (heterozygotes) often do not show symptoms because they have another X chromosome with a normal allele.
• Males, on the other hand, will display the trait if their single X chromosome is affected since the Y chromosome does not carry a backup allele for the trait.

This mechanism explains why diseases like hemophilia are more common in males, and why carrier females can pass the trait to their sons.

Genotype Analysis in X-linked Traits

Genotype analysis helps to determine which alleles an individual has for a particular trait. When analyzing X-linked inheritance, such as hemophilia:

• Understand the possible genotypes for males: They can be either normal ( \(X^HY\) ) or affected ( \(X^hY\) ).
• For females, they have the potential for three genotypes: unaffected carriers ( \(X^HX^h\) ), unaffected non-carriers ( \(X^HX^H\) ), or affected ( \(X^hX^h\) ).

To predict the probability of an offspring inheriting a particular trait, parents' genotypes are analyzed to see what combinations of alleles can result. In the case of Sally and Sam's family, Sally is a carrier ( \(X^HX^h\)), and Sam is unaffected ( \(X^HY\)). Their offspring's genotypes demonstrate how carriers and affected individuals can result from these x-linked recessive inheritance patterns.