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Modern Genetic Analysis Chapter 12. Genomics
Solved Problem

2.

Duchenne muscular dystrophy (DMD) is an X-linked recessive human disease affecting muscles. Six small boys had DMD, together with various other disorders, and they were found to have small deletions of the X chromosome, as shown here:

a. On the basis of this information, which chromosomal region most likely contains the gene for DMD?
b. Why did the boys show other symptoms in addition to DMD?
c. How would you use DNA samples from these six boys and DNA from unaffected boys to obtain an enriched sample of DNA containing the gene for DMD, as a prelude to cloning the gene?
See answer

Solution
a. The only region that all the deletions are lacking is the chromosomal region labeled 5, so this presumably contains the gene for DMD.
b. The other symptoms probably result from the deletion of the other regions surrounding the DMD region.
c. If the DNA from all the DMD deletions is denatured (i.e., its strands separated) and bound to some kind of filter, the normal DNA can be cut by shearing or by restriction-enzyme treatment, denatured, and passed through the filter containing the deleted DNA. Most DNA will bind to the filter, but the region-5 DNA will pass through. This process can be repeated several times. The filtrate DNA can be cloned and then used in a FISH analysis to see if it binds to the DMD X chromosomes. If not, it becomes a candidate for the DMD-containing sequence.
See question

© 1999 by W. H. Freeman and Company. All rights reserved.