Why are genetic variants with large effects on traits generally rarer than those with smaller effects? Explain how this relates to the observation that the heritability of common diseases is driven by common variants

Why are genetic variants with large effects on traits generally rarer than those with smaller effects? Explain how this relates to the observation that the heritability of common diseases is driven by common variants

Name: Why are genetic variants with large effects on traits generally rarer
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Description: Why are genetic variants with large effects on traits generally rarer than those with smaller effects? Explain how this relates to the observation that the heritability of common diseases is driven by common variants

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter18: Genetics Of Behavior

Section: Chapter Questions

Problem 14QP: A pedigree analysis was performed on the family of a man with schizophrenia. Based on the known...

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A woman diagnosed with early-onset Alzheimer's due to a mutation of the APP genehas children with a man that has no family history of familial Alzheimer's. Give the probability of each possible genotype with corresponding phenotype. (The woman has two possible allele combinations. You must show both possibilities)
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One particularly useful feature of the Hardy-Weinberg equation is that it allows us to estimate the frequency of heterozygotes for recessive genetic diseases, assuming that Hardy-Weinberg equilibrium exists. As an example, let’s consider cystic fibrosis, which is a human genetic disease involving a gene that encodes a chloride transporter. Persons with this disorder have an irregularity in salt and water balance. One of the symptoms is thick mucus in the lungs that can contribute to repeated lung infections. In populations of Northern European descent, the frequency of affected individuals is approximately 1 in 2500. Because this is a recessive disorder, affected individuals are homozygotes. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of individuals who are heterozygous carriers?
In Huntington’s disease, the wild-type allele, h, is recessive to the disease allele, H. The persistence of an autosomal dominant allele that is fatal in 100% of cases is best explained by which of the following? A) The dominant allele only has moderate negative effects during adolescence and young adulthood. B) The wild-type h allele continues to spontaneously mutate into the dominant H allele. C) The persistence of any given allele in nature is determined almost wholly by chance. D) The disease has no effects until the individual has reached an age far past the normal age for reproduction.
Why are the concepts of variable expressivity, incomplete penetrance, and delayed age of onset so important in relation to genetic diseases?
A pedigree analysis was performed on the family of a man with schizophrenia. Based on the known concordance statistics, would his MZ twin be at high risk for the disease? Would the twins risk decrease if he were raised in an environment different from that of his schizophrenic brother?
Explain why most loss-of-function alleles are recessive to wild-type, but some are incompletely dominant or (rarely) dominant?
Which of the following best explains how individuals who inherit phenylketonuria alleles can avoid the symptoms of this disease (mental impairment, foul smelling urine)? It exhibits variable expressivity. The expression of this disease depends on the environment. If the individual removes phenylalanine from their diet they can avoid the disease entirely. PKU alleles are epistatic to alleles of another gene, which acts downstream in phenylalanine metabolism. These individuals supplement their diets with enzymes that break-down phenylalanine.
Many genetic disorders exhibit locus heterogeneity. Define andgive two examples of locus heterogeneity. How does locus heterogeneityconfound a pedigree analysis?
Huntington disease (HD) is a rare dominant condition in humans that results in a slow but inexorable deterioration of the nervous system. HD shows what might be called “age-dependent penetrance,” which is to say that the probability that a person with the HD genotype will express the phenotype varies with age. Assume that 50% of those inheriting the HD allele will express the symptoms by age 40. Susan is a 35-year-old woman whose father has HD. She currently shows no symptoms. What is the probability that Susan will show symptoms in five years?
Explain the following features of the Mendelian traits and fill the Punnet Squares. a)The disappearance of recessive phenotype in the F1 generation. b)The genotype of an individual expressing dominant phenotype can be differentiated by the test cross.