Chapter 8, Problem 45P

Adermatoglyphia (described previously in Problem 18 in Chapter 3) is an extremely rare condition where people are born without fingerprints; only four families on earth are known to have this condition. The condition is inherited in an autosomal dominant fashion and is due to point mutations in a gene on chromosome 4 called SMARCAD1.

The following figure shows that different point mutations—all near the 5′ end of the same intron of SMARCAD1—were found in each of the four families. All four mutations prevent the expression of a skin-specific transcript that uniquely contains exon 1, the first exon of this transcript; no other SMARCAD1 mRNAs contain this exon. In the figure, the final three bases in the RNA-like strand of exon 1 are shaded, while the first six bases of intron 1 are unshaded.

a.	No ATG sequence normally exists in exon 1 upstream of the sequence shown. Which part of the skin-specific mRNA corresponds to exon 1?
b.	What aspect of gene expression is likely to be affected most directly by these mutations?
c.	Are these mutations more likely to cause loss of function or gain of function?