Concept explainers
To analyze:
Describe following on the basis of an autosomal recessive condition:
The chance that the first child will be homozygous recessive for mutation, if both parents are heterozygous carriers of a mutant allele
Parents who are heterozygous carriers for a recessive mutant allele have a normal child. Determine the chance that this child is a heterozygous carrier of the condition.
If parents are heterozygous carriers of a mutant allele, and have the first child with homozygous recessive condition, calculate the probability that the second child of the couple will be homozygous recessive. Also calculate the probability that the second child will be a heterozygous carrier of the condition.
Introduction:
In an autosomal recessive condition, both copies of alleles are responsible for a trait and should be recessive (abnormal) to cause a disease. The diseased condition cannot be observed in an individual with a homozygous dominant or heterozygous dominant allele, but heterozygous dominant are the carrier for the trait.
Phenylketonuria (PKU) is an autosomal recessive disorder and can be observed in individuals who have both the copies of alleles in a homozygous recessive condition.
Explanation of Solution
Pedigree chart of cross between both heterozygous parents
♂ ♀ |
A | a |
A | AA | Aa |
a | Aa | aa |
The
Homozygous dominant (AA) is
Heterozygous carrier (Aa) is
Homozygous recessive (aa) is
The chance that the first child of the couple will be homozygous recessive (aa) for the mutation is
In this part, they have asked to estimate the probability of a normal child being a carrier for the mutation.
The chance of having normal (AA / Aa) child is
Since the birth of the second child is independent of the birth of first child so, the chance of the second child of the couple will be homozygous recessive (aa) for the mutation is
The chance of the second child of the couple will be heterozygous carrier (Aa) for the mutation is
The chance that the first child of the couple will be homozygous recessive (aa) for the mutation is
The chance of the normal child being a carrier for the condition is
The chance that the second child of the couple will be homozygous recessive (aa) for the mutation is
The chance that the second child of the couple will be a heterozygous carrier (Aa) for the mutation is
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Chapter B Solutions
Genetic Analysis: An Integrated Approach Plus Mastering Genetics with Pearson eText -- Access Card Package (3rd Edition) (What's New in Genetics)
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- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning