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Ch. 2 - Transmission Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 15a
Chapter 2, Problem 15a

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.
Pedigree chart illustrating the inheritance of albinism in a human family across two generations.
What is the most likely mode of transmission of albinism in this family? 

Verified step by step guidance
1
Analyze the pedigree to determine the inheritance pattern. Look for key indicators such as whether the trait skips generations, affects both sexes equally, or is passed from parent to child directly.
Recall that albinism is typically caused by mutations in genes involved in melanin production, such as the TYR gene. It is often inherited in an autosomal recessive manner, meaning two copies of the mutated gene are required for the trait to manifest.
Check if individuals with albinism in the pedigree have parents who do not exhibit the trait. This would suggest that the parents are carriers (heterozygous) for the recessive allele.
Verify if the trait affects both males and females equally in the pedigree. If it does, this supports the hypothesis of autosomal inheritance rather than sex-linked inheritance.
Conclude that the most likely mode of transmission is autosomal recessive if the above criteria are met. If the pedigree does not match these characteristics, consider alternative modes of inheritance such as autosomal dominant or X-linked recessive.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance patterns of traits through generations in a family. It helps identify whether a trait is dominant or recessive, and whether it is linked to sex chromosomes. By examining the pedigree, one can determine how albinism is passed down and predict its occurrence in future generations.
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Pedigree Flowchart

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only when an individual has two copies of the recessive allele, one inherited from each parent. In the case of albinism, if both parents are carriers (heterozygous) for the albinism allele, there is a 25% chance with each pregnancy that their child will be affected. This mode of inheritance often results in affected individuals appearing in families without a prior history of the condition.
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Autosomal Pedigrees

Phenotype vs. Genotype

The phenotype refers to the observable characteristics or traits of an organism, such as skin pigmentation, while the genotype is the genetic makeup that determines these traits. In the context of albinism, individuals with the phenotype of albinism have a specific genotype that includes two recessive alleles. Understanding the distinction between these concepts is crucial for interpreting the pedigree and determining the mode of inheritance.
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Related Practice
Textbook Question

An experienced goldfish breeder receives two unusual male goldfish. One is black rather than gold, and the other has a single tail fin rather than a split tail fin. The breeder crosses the black male with a female that is gold. All the F₁ are gold. She also crosses the single-finned male to a female with a split tail fin. All the F₁ have a split tail fin. She then crosses the black male to F₁ gold females and, separately, crosses the single-finned male to F₁ split-finned females. The results of the crosses are shown below.


  Black male x F₁ gold female:

    Gold        32

    Black       34

  Single-finned male x F₁ split-finned female:

    Split fin       41

    Single fin    39

What do the results of these crosses suggest about the inheritance of color and tail fin shape in goldfish?

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Textbook Question

An experienced goldfish breeder receives two unusual male goldfish. One is black rather than gold, and the other has a single tail fin rather than a split tail fin. The breeder crosses the black male to a female that is gold. All the F₁ are gold. She also crosses the single-finned male to a female with a split tail fin. All the F₁ have a split tail fin. She then crosses the black male to F₁ gold females and, separately, crosses the single-finned male to F₁ split-finned females. The results of the crosses are shown below.

Is black color dominant or recessive? Explain. Is single tail dominant or recessive? Explain.

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Textbook Question

An experienced goldfish breeder receives two unusual male goldfish. One is black rather than gold, and the other has a single tail fin rather than a split tail fin. The breeder crosses the black male to a female that is gold. All the F₁ are gold. She also crosses the single-finned male to a female with a split tail fin. All the F₁ have a split tail fin. She then crosses the black male to F₁ gold females and, separately, crosses the single-finned male to F₁ split-finned females. The results of the crosses are shown below.

  Black male x F₁ gold female:

    Gold         32

    Black        34

  Single-finned male x F₁ split-finned female:

    Split fin        41

    Single fin     39

Use chi-square analysis to test your hereditary hypothesis for each trait.

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

Using allelic symbols of your choice, identify the genotypes of the male and his two mates in generation I. 

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

The female I-1 and her mate, male I-2, had four children, one of whom has albinism. What is the probability that they could have had a total of four children with any other outcome except one child with albinism and three with normal pigmentation? 

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Textbook Question

The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

What is the probability that female I-3 is a heterozygous carrier of the allele for albinism? 

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