The pedigree shows the segregation of an autosomal recessive trait. Assume that the mutant allele is a and the normal allele is A; what is the genotype of III-4? Generation 1 has a couple where the male and female are both unaffected. The couple has 1 unaffected daughter and 1 affected son in generation 2. The unaffected female from generation 2 mates with an unaffected male and has 1 unaffected daughter and 1 affected son in generation 3. The affected male from generation 2 mates with an unaffected female and has 1 unaffected daughter and 2 unaffected sons in generation 3. The affected male from generation 3 mates with an unaffected female and has 1 unaffected daughter in generation 4. Unaffected daughter of unaffected female from generation 2 mates with an unaffected male and has 1 affected daughter and 1 affected son in generation 4. Unaffected daughter of affected male from generation 2 mated with an unaffected male and has 2 affected sons and 1 unaffected son in generation 4. Unaffected daughter of affected male from generation 3 mates with an unaffected male and has 2 unaffected daughters and 2 unaffected sons in generation 5. Click image to view full size. Aa XAXXa aa AA
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Step 1: The unaffected individuals are represented by the genotype AA, and the affected individuals are represented by the genotype aa. Show more…
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Mode of inheritance: autosomal dominant. Assume the trait is rare in the population. ONE mode applies to all 3 pedigrees. 1. In this pedigree, every affected individual had at least one parent that was affected by the disease. It occurred in every generation in this pedigree. 2. Affected males did not have affected daughters only and unaffected males because it was noted that there were affected sons as well. 2. Give two reasons that support your choice: 1. It cannot be X-linked dominant because in the third pedigree, more males are affected whereas in X-linked dominant, more females are affected by the disease. Also, the disease in X-linked is passed from an affected father to all affected daughters, which is not the case in this pedigree. 2. It cannot be autosomal recessive because both parents are affected in autosomal recessive and it did not skip a generation. 3. It cannot be X-linked recessive because in X-linked recessive, more males are affected, but in our pedigree, we see both females and males are affected. In X-linked recessive, we should see more affected sons from an affected mother. But in this pedigree, we also had affected mothers to affected females. 4. Genotypes for EACH individual in all three pedigrees. Write genotypes ON THE PEDIGREE SHEET using allele symbols appropriate for the mode of inheritance:
Josee P.
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Shyam P.
Pedigree 1. draw a simple pedigree of four generations in the space provided below. The original parents have been drawn for you. They produce a male and female child. The male child marries and has two sons. The female child marries and gives birth to two daughters. One of her daughters marries, and has a son and a daughter. The female in the first generation, the son in the second generation, and both children in the fourth generation express the trait. Analysis of a pedigree We need to determine if the trait is dominant or recessive, and whether it is sex-linked. Consider the following questions: 1. Is a trait that appears in each generation more likely to be dominant or recessive? 2. Does the trait appear in both males and females? With the same frequency? 3. Can the mode of inheritance of the trait in Pedigree 1 be autosomal recessive? autosomal dominant? Why or why not? 4. Can the mode of inheritance of the trait in Pedigree 1 be sex-linked? Why or why not? 5. Can parents who are affected have unaffected children if the trait were dominant?
Suman K.
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