Question

For the following pedigree (Pedigree Tree I, used for following questions, too), decide whether a trait is inherited as an autosomal dominant, autosomal recessive, or X-linked recessive. 2 10 11 po og po 0000 TO 1 2 3 4 5 12 13 14 Autosomal dominant Most likely autosomal recessive Most likely X-linked recessive Autosomal recessive X-linked recessive Either autosomal recessive or X-linked recessive QUESTION 4 (Pedigree Tree 1) What is the genotype of Generation individual 12 АА ОАа Оаа Either AA or Аа O XAXA Охха Either XAXA or хха Ο χΑν Ο χών Cannot determine with the information provided QUESTION 5 (Pedigree Tree 1) What is the genotype of Generation II, individual 17 0АА ОАа Оаа Either AA or Aa O XAXA Охха Either XAXA or XAX OXAY OXY Cannot determine with the information provided QUESTION 6 (Pedigree Tree ) What is the genotype of Generation III, individual 8? Either AA or Either XAXA or Cannot determine with the

Answer 1

For the given pedigree chart, we have three options for the nature of the disease being studied: autosomal dominant, autosomal recessive and X-linked recessive.

Let us work with a system of elimination:

While neither parents in generation I show a diseased phenotype, two out of seven offspring show a diseased phenotype. This is not possible in any case of dominant allele-linked disease.

Now, we need to decide if its X-linked recessive or autosomal recessive. Consider the following cases:

• The cross between individuals 2 and 3 in generation II, produces four male offspring out of which three are diseased. As the female parent is diseased, she would have a recessive phenotype. Suppose the disease allele was X-linked recessive, the female parent would give all her male offspring the disease allele on her X-chromosome and thus, all her male offsprings would be diseased. However, this is not the case.
• The cross between the two healthy parents in Generation I yields two female diseased offsprings (1 and 6, out of 7 total offsprings). In a case of X-linked recessive disease allele, the production of a diseased female offspring necessarily implies that the male parent is diseased too. However, this is not the case.

Both the above evidences sufficiently prove that the disease allele is autosomal recessive.

Having determined this, we can answer the remaining questions.

Answer to Question 4: Being a diseased individual from an autosomal recessive disorder, the genotype would be aa (third option).

Answer to Question 5: Being a diseased individual from an autosomal recessive disorder, the genotype would be aa (third option).

Answer to Question 6: Since the concerned individual is a healthy offspring of one diseased and one healthy parent, its genotype would be Aa (second option).