Sapling Learning John and Sue are expecting a child, but are concerned about a r

Question

Sapling Learning John and Sue are expecting a child, but are concerned about a rare autosomal recessive disease that is present in both of their families, in the pedigree represented as individual I11-12. John's sister, IlI-10, and Sue's brother, I1-13, both do n the disease, but John's paternal grandmother and Sue's maternal grandfather both had the disease. below, John is represented as individual I11-11 and Sue is Assign the appropriate symbol to each individual in the pedigree. 6 10 12 13 What is the probability that John is a carrier? What is the probability that both John and Sue are carriers? Number Number Tools

Explanation / Answer

The probability that John is a carrier is 50%.

The probability that both John and Sue are carriers is 25%.

It is given that the disease they are concerned about is an autosomal recessive disease. That means both parents have to be carriers and in the genotype of the affected both alleles are of disease type.

Suppose, the infected allele is - a and the normal allele of the gene is - A

Since it is a recessive disease-

the unaffected would have - AA

The carrier would have - Aa

the affected/ diseased would have - aa

Since the disease is autosomal, there is no sex- bias.

Proceeding to the problem,

Both of John's parents are carriers i.e. Aa

So for John (Aa x Aa),

the probability of AA= 0.25 or 25%; the prob. of Aa = 0.5 or 50% and the prob. of aa = 0.25 or 25%

Similarly, for Sue, her mother is a carrier(Aa) and her father is unaffected(AA)

Hence for Sue(Aa x AA),

the prob. of AA = 0.5 and the prob. of Aa = 0.5

For both John and Sue to be carriers, the probability = 0.5 * 0.5 = 0.25 or 25%

Therefore,

The prob. of John to be a carrier= 50%.

The prob. of both John and Sue to be carriers is = 25%.

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