Lecture 7 Answers - Lecture 7: Study Questions and Answers...

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Lecture 7 : Study Questions and Answers 1. What three factors complicate the task of studying the inheritance of human characteristics? (1) Mating cannot be controlled. It is not ethical or feasible to set up controlled matingexperiments. (2) Humans have a long generation time, so it takes a long time to track inheritance of traits over more than one generation. (3) The number of progeny per mating is limited, so phenotypic ratios are uncertain. 2. Who is the proband in a pedigree? Is the proband always found in the last generation of the pedigree? Why or why not? The proband is the person of interest for whom the pedigree chart has been drawn. The proband is not necessarily found in the last generation because the proband’s children, or the children of the proband’s siblings, often provide information about the genotype of the proband. 3. For each of the following modes of inheritance, describe the features that will be exhibited in a pedigree in which the trait is present: autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant, and Y-linked inheritance. Pedigrees with autosomal recessive traits will show affected males and females arising with equal frequency from unaffected parents. The trait often appears to skip generations. Unaffected people with an affected parent will be carriers. Pedigrees with autosomal dominant traits will show affected males and females arising with equal frequency from a single affected parent. The trait does not usually skip generations. X-linked recessive traits will affect males predominantly and will be passed from an affected male through his unaffected daughter to his grandson. X-linked recessive traits are not passed from father to son. X-linked dominant traits will affect males and females and will be passed from an affected male to all his daughters, but not to his sons. An affected woman (usually heterozygous for a rare dominant trait) will pass on the trait equally to half her daughters and half her sons. Y-linked traits will show up exclusively in males, passed from father to son. 4. How does the pedigree of an autosomal recessive trait differ from the pedigree of an X-linked recessive trait? Pedigrees of autosomal recessive traits will have equal frequencies of affected males and females, whereas pedigrees of X-linked recessive traits will show mostly affected males. Also, both parents must be carriers to have children with autosomal recessive traits, whereas a mother carrying an X-linked trait can have
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affected sons regardless of the genotype of the father. Finally, an X-linked trait is never passed from the father to his sons. 5. Other than the fact that a Y-linked trait appears only in males, how does the pedigree of a Y-linked trait differ from the pedigree of an autosomal dominant trait? A Y-linked dominant trait is passed from a father to all of his sons, whereas an
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Lecture 7 Answers - Lecture 7: Study Questions and Answers...

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