Question

Each of the four pedigrees that follow represents a human family within which a genetic disease is segregating. Affected individuals are indicated by filled-in symbols. One of the diseases is transmitted as an autosomal recessive condition, one as an X-linked recessive, one as an autosomal dominant, and one as an X-linked dominant. Assume all four traits are rare in the population and completely penetrant.
Required:
a. Indicate which pedigree represents which mode of inheritance, and explain how you know.
b. For each pedigree, what would you tell the parents about the chance that their child (indicated by the hexagon shape) will have the condition?

Answer 1

 Answer:

The following four traits are -:

• Pedigree 1 - A recessive trait (autosomal recessive)  is expressed by pedigree 1.
• Pedigree 2- Recessive inheritance is defined by Pedigree 2.
• Pedigree 3 - The inheritance of the dominant trait (autosomal dominant) is illustrated by Pedigree 3.
• Pedigree 4- An X-like dominant trait is expressed by Pedigree 4.    

Explanation:

Explaination of each pedigree chart-

• Pedigree 1 demonstrates the recessive trait since their children have been affected by two unaffected individuals. If the characteristics were X-linked, in order to have an affected daughter, I-1 would have to be affected. $X^A$ In this, both parents are autosomal recessive trait carriers, so the child will be affected by a 1/4 (aa)
• Recessive inheritance is defined by Pedigree 2. This is X-related inheritance as autosomal recessive inheritance has already been accounted for in part 1. This inference is confirmed by evidence showing that the father (I-1) is unaffected and that only the sons exhibit the characteristic in generation II, suggesting that the mother must be the carrier. The individual I-2 is a carrier for this X-linked trait. A typical  Xa chromosome is attached to the unaffected father (I-1), so the chance of carrier II-5 is 1/2. Probability of an affected son = 1/2 (probability II-5 is a carrier) x 1/2 (probability II -5 contributes ($X^A$) x 1/2 (probability of Y from father II-6) = 1/8. An affected daughter's likelihood is 0 because a typical $X^A$ must be contributed by II-6.
• The inheritance of the dominant trait is demonstrated by Pedigree 3 because affected children still have affected parents (remember that all four diseases are rare). The trait must be autosomal dominant because it is passed down to the son by the affected father. There is a 1/2 risk that the heterozygous mother (II-5) would pass on mutant alleles to a child of either sex for an autosomal dominant feature.
• Pedigree 4 is an X-linked dominant function characterized by the transmission to all of his daughters from the affected father but none of his son. On the mutant X chromosome, the father (I-1) passes on to all his daughters and none of his sons. As seen by his normal phenotype, II-6 therefore does not bear the mutation. An affected child's likelihood is 0.    

In the question the pedigree chart was missing ,hence it is given below.