2. Mendel's Laws of Inheritance

Pedigrees

2. Mendel's Laws of Inheritance

Pedigrees

3:28 minutes

Problem 30a

Textbook Question

Consider the three pedigrees below, all involving a single human trait.

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

Verified step by step guidance

Step 1: Identify the pattern of affected individuals in each pedigree. Note the sex of affected individuals (squares for males, circles for females) and whether the trait appears in every generation or skips generations.

Step 2: For autosomal dominant traits, affected individuals usually appear in every generation and both males and females are equally likely to be affected. Check if this pattern fits any of the pedigrees.

Step 3: For X-linked dominant traits, affected males pass the trait to all daughters but no sons, and affected females can pass it to both sons and daughters. Look for affected females in every generation and affected males passing the trait to daughters.

Step 4: For autosomal recessive traits, the trait can skip generations, and affected individuals can have unaffected parents. Both males and females are equally affected. Check if the trait appears in siblings but not parents.

Step 5: For X-linked recessive traits, more males are affected than females, and affected males usually inherit the trait from carrier mothers. Affected males do not pass the trait to sons but can pass the allele to daughters who become carriers. Look for this pattern in the pedigrees.

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Key Concepts

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

Modes of Inheritance

Modes of inheritance describe how traits are passed from parents to offspring. Common types include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Each mode has distinct patterns in pedigrees, such as affected individuals in every generation for dominant traits or skipping generations for recessive traits.

Pedigree Analysis

Pedigree analysis involves studying family trees to track the inheritance of traits. Squares represent males, circles represent females, and shaded symbols indicate affected individuals. By examining affected and unaffected members across generations, one can infer the likely mode of inheritance.

X-linked vs Autosomal Traits

X-linked traits are associated with genes on the X chromosome and often show different patterns between males and females, such as males being more frequently affected in X-linked recessive traits. Autosomal traits are located on non-sex chromosomes and typically affect males and females equally.

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Related Practice

Textbook Question

A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait.

Consider the three pedigrees below, all involving a single human trait.

Given your conclusions in part (a), indicate the genotype of the following individuals: II-1, II-6, II-9 If more than one possibility applies, list all possibilities. Use the symbols A and a for the genotypes.

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Textbook Question

Consider the three pedigrees below, all involving a single human trait.

For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

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Textbook Question

The gene controlling the Xg blood group alleles (Xg⁺ and Xg⁻) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness (EMWX) (Ryan et al., 1999) are closely linked on the X chromosome in humans at position Xp22.3 (the tip of the short arm). A male with EMWX who is Xg⁻ marries a woman who is Xg⁺ and they have eight daughters and one son, all of whom are normal for muscle function, the male being Xg⁺ and all the daughters being heterozygous at both the EMWX and Xg loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children. Create a pedigree that represents all data stated above and in the following table.

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Textbook 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?

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Textbook Question

The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family.

Excluding II-4, what is the genotype of each family member for the disease gene?

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Textbook Question

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.

Draw a pedigree that includes Amanda, Brice, and their siblings and parents. Identify the genotype of each person, using G and g to represent the dominant and recessive alleles, respectively.

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Show more practices

Consider the three pedigrees below, all involving a single human trait.Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

Key Concepts

Modes of Inheritance

Pedigree Analysis

X-linked vs Autosomal Traits

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Consider the three pedigrees below, all involving a single human trait.

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal