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Chapter 4: Problem 24

Let's suppose you have pedigree data from thousands of different families involving a particular genetic disease. How would you decide whether the disease is inherited as a recessive trait as opposed to one that is dominant but shows incomplete penetrance?

Short Answer

Expert verified
The distinction between a recessive trait and a dominant one with incomplete penetrance depends on the pattern of the disease's spread across generations. If the disease often skips generations and appears in individuals without a parental case, it's likely recessive. If the disease usually passes directly from parent to child, with only occasional non-affected instances despite the presence of the gene, it's likely a dominant trait with incomplete penetrance.

Step by step solution

01

Understanding Recessive and Dominant Traits

Recessive traits are observed only when two copies of the gene, one from each parent, are present. Dominant traits express themselves even if only one copy of the gene is inherited. Incomplete penetrance occurs when an individual inherits a dominant gene but the trait is not expressed.
02

Analyzing Pedigree Data

Examine the pedigree data. For a recessive trait, the disease is likely to skip generations as it only exhibits when an individual has two copies of the disease gene. The disease would exhibit in individuals who may not have any ancestors with the disease, because each parent can carry a single recessive copy without manifestation. In a dominant trait with incomplete penetrance, the affected individuals will frequently have an affected parent, since the disease can be expressed even if only one copy of the gene is inherited. The disease does not typically skip generations unless it exhibits incomplete penetrance. In this case, an affected individual may have an affected parent who does not show the disease because the gene is not expressing itself (penetrance is incomplete).
03

Making Determination

Based on the analysis of the pedigree data, a determination can be made regarding the nature of the disease trait. If the disease strikes even when the parent generation does not show symptoms, it is likely a recessive trait. However, if the disease is present in consecutive generations but isn't ubiquitous (some carrying gene do not show it), it is indicative of a dominant trait with incomplete penetrance.

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Most popular questions from this chapter

In rabbits, the color of body fat is controlled by a single gene with two alleles, designated \(Y\) and \(y\). The outcome of this trait is affected by the diet of the rabbit. When raised on a standard vegetarian diet, the dominant \(Y\) allele confers white body fat, and the \(y\) allele confers yellow body fat. However, when raised on a xanthophyll-free diet, a homozygote \(y y\) rabbit has white body fat. If a heterozygous rabbit is crossed to a rabbit with yellow body fat, what are the proportions of offspring with white and yellow body fat when raised on a standard vegetarian diet? How do the proportions change if the offspring are raised on a xanthophyll-free diet?

Describe the differences among dominance, incomplete dominance, codominance, and overdominance.

In cats, a temperature-sensitive allele produces the Siamese phenotype, in which the cooler extremities are dark and the warmer trunk area is lighter. A Siamese cat that spends most of its time outside was accidentally injured in a trap and required several stitches in its right front paw. The veterinarian had to shave the fur from the paw and leg, which originally had rather dark fur. Later, when the fur grew back, it was much lighter than the fur on the other three legs. Do you think this injury occurred in the hot summer or cold winter? Explain your answer.

A type A woman is the daughter of a type \(\mathrm{O}\) father and a type \(\mathrm{A}\) mother. If she has children with a type \(\mathrm{AB}\) man, what are the following probabilities? A. A type \(\mathrm{AB}\) child B. A type \(O\) child C. The first three children with type \(A B\) D. A family composed of two children with type B blood and one child with type \(\mathrm{AB}\)

A nectarine is a peach without the fuzz. The difference is controlled by a single gene that is found in two alleles, \(D\) and \(d\). At the molecular level, do you think that the nectarine is homozygous for a recessive allele or that the peach is homozygous for the recessive allele? Explain your reasoning.
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