Suppose that Gene A corresponds to a human disease gene. Many patients had their

Question

Suppose that Gene A corresponds to a human disease gene. Many patients had their genomic DNA isolated and amplified for the Gene A region. The PCR products were digested with the endonuclease EcoRI. The following pattern was found for the different patients.

The patients do NOT necessarily have the disease. From the pattern of digestion, answer the following:

A. Which patient(s) could be normal for the disease?

B. Which patient(s) are likely to have the disease?

C. Which patient(s) could be haploinsufficient and show the disease?

D. Assuming no haploinsufficency among the alleles, suppose that patient 1 and 6 had a child. What is the probability that a child will be affected?

E. Assuming no haploinsufficency among the alleles, suppose that patient 3 and 4 had a child. What is the probability that a child will be affected?

F. Draw a map of gene A and indicate possible sites for the mutations and EcoRI site(s).

Explanation / Answer

A. Pt-1, Pt-2, and Pt-6 could be normal for the disease as they show characteristic two bands found in the normal sample (This holds true only if it is a recessive disorder).

B. Pt-3,4, and 5 could be affected with the disease as they do not show characteristic banding pattern that is seen in normal condition.

C. Pt-1 and Pt-6 could be haploinsufficient (heterozygous for the disease-causing allele).

D. Pt-1 and Pt-6 are heterozygous for the disease allele.

Parental cross: Aa X Aa

Progeny: AA Aa Aa aa

1/4th of their progeny are likely to be affected.

E. Both 3 and four are homozygous for the disease allele. So, all of their progeny will be affected.

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