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Ch. 3 - Cell Division and Chromosome Heredity
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 3, Problem 13a

In humans, hemophilia A (OMIM 306700) is an X-linked recessive disorder that affects the gene for factor VIII protein, which is essential for blood clotting. The dominant and recessive alleles for the factor VIII gene are represented by H and h. Albinism is an autosomal recessive condition that results from mutation of the gene producing tyrosinase, an enzyme in the melanin synthesis pathway. A and a represent the tyrosinase alleles. A healthy woman named Clara (II-2), whose father (I-1) has hemophilia and whose brother (II-1) has albinism, is married to a healthy man named Charles (II-3), whose parents are healthy. Charles's brother (II-5) has hemophilia, and his sister (II-4) has albinism. The pedigree is shown below.
Pedigree chart showing inheritance patterns of hemophilia and albinism in two families, highlighting Clara and Charles.
What are the genotypes of the four parents (I-1 to I-4) in this pedigree?

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1
Step 1: Understand the inheritance patterns. Hemophilia A is X-linked recessive, meaning males (XY) with the recessive allele (h) will express the disorder, while females (XX) must have two recessive alleles (hh) to express it. Albinism is autosomal recessive, meaning individuals must inherit two recessive alleles (aa) to express the condition.
Step 2: Analyze the pedigree for hemophilia. Clara's father (I-1) has hemophilia, so his genotype must be XʰY. Clara (II-2) is healthy but her father passed on his Xʰ chromosome, so her genotype must be XʰX. Charles's brother (II-5) has hemophilia, so their mother (I-3) must be a carrier (XʰX) and their father (I-4) must be XʜY.
Step 3: Analyze the pedigree for albinism. Clara's brother (II-1) has albinism, so both parents (I-1 and I-2) must carry the recessive allele (Aa). Charles's sister (II-4) has albinism, so both parents (I-3 and I-4) must also carry the recessive allele (Aa).
Step 4: Combine the information for Clara's parents. Clara's father (I-1) is XʰY and Aa (carrier for albinism). Clara's mother (I-2) is XʜX and Aa (carrier for albinism).
Step 5: Combine the information for Charles's parents. Charles's father (I-4) is XʜY and Aa (carrier for albinism). Charles's mother (I-3) is XʰX and Aa (carrier for albinism).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

X-linked Recessive Inheritance

X-linked recessive inheritance refers to traits that are associated with genes located on the X chromosome. In this pattern, males (XY) are more likely to express the trait because they have only one X chromosome, while females (XX) can be carriers if they have one affected X and one normal X. Hemophilia A is a classic example, where affected males inherit the disorder from carrier mothers.
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X-Inactivation

Autosomal Recessive Inheritance

Autosomal recessive inheritance involves genes located on non-sex chromosomes (autosomes). For an individual to express a recessive trait, they must inherit two copies of the recessive allele, one from each parent. Albinism, caused by mutations in the tyrosinase gene, exemplifies this inheritance pattern, where both parents must carry at least one recessive allele for their child to be affected.
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Autosomal Pedigrees

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance of traits through generations in a family. It helps identify the genotypes of individuals based on their phenotypes and the phenotypes of their relatives. By analyzing the pedigree provided in the question, one can deduce the genotypes of the parents based on the inheritance patterns of hemophilia and albinism in their offspring.
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Pedigree Flowchart
Related Practice
Textbook Question

A woman's father has ornithine transcarbamylase deficiency (OTD), an X-linked recessive disorder producing mental deterioration if not properly treated. The woman's mother is homozygous for the wild-type allele.


If the woman has a daughter with a man who does not have OTD, what is the chance the daughter will be a heterozygous carrier of OTD? What is the chance the daughter will have OTD?

Textbook Question

A woman's father has ornithine transcarbamylase deficiency (OTD), an X-linked recessive disorder producing mental deterioration if not properly treated. The woman's mother is homozygous for the wild-type allele.


Identify a male with whom the woman could produce a daughter with OTD.

Textbook Question

A woman's father has ornithine transcarbamylase deficiency (OTD), an X-linked recessive disorder producing mental deterioration if not properly treated. The woman's mother is homozygous for the wild-type allele.


What proportion of daughters produced by the woman and the man are expected to have OTD? What proportion of sons of the woman and the man are expected to have OTD?

Textbook Question

In humans, hemophilia A (OMIM 306700) is an X-linked recessive disorder that affects the gene for factor VIII protein, which is essential for blood clotting. The dominant and recessive alleles for the factor VIII gene are represented by H and h. Albinism is an autosomal recessive condition that results from mutation of the gene producing tyrosinase, an enzyme in the melanin synthesis pathway. A and a represent the tyrosinase alleles. A healthy woman named Clara (II-2), whose father (I-1) has hemophilia and whose brother (II-1) has albinism, is married to a healthy man named Charles (II-3), whose parents are healthy. Charles's brother (II-5) has hemophilia, and his sister (II-4) has albinism. The pedigree is shown below.

Determine the probability that the first child of Clara and Charles will be a


i. boy with hemophilia

ii. girl with albinism

iii. healthy girl

iv. boy with both albinism and hemophilia

v. boy with albinism

vi. girl with hemophilia

Textbook Question

In humans, hemophilia A (OMIM 306700) is an X-linked recessive disorder that affects the gene for factor VIII protein, which is essential for blood clotting. The dominant and recessive alleles for the factor VIII gene are represented by H and h. Albinism is an autosomal recessive condition that results from mutation of the gene producing tyrosinase, an enzyme in the melanin synthesis pathway. A and a represent the tyrosinase alleles. A healthy woman named Clara (II-2), whose father (I-1) has hemophilia and whose brother (II-1) has albinism, is married to a healthy man named Charles (II-3), whose parents are healthy. Charles's brother (II-5) has hemophilia, and his sister (II-4) has albinism. The pedigree is shown below.

If Clara and Charles's first child has albinism, what is the chance the second child has albinism? Explain why this probability is higher than the probability you calculated in part (b).

Textbook Question

A wild-type male and a wild-type female Drosophila with red eyes and full wings are crossed. Their progeny are shown below.

Using clearly defined allele symbols of your choice, give the genotype of each parent.