Chapter 4, Problem 51P

The pedigree diagram below shows a family in which many individuals are affected by a disease called Leri-Weill dyschondrosteosis (LWD). People with LWD are short in stature due to leg bone deformities; arm bones are also malformed in some individuals. The mutant gene responsible for LWD was identified in 1998 as SHOX, a gene located in a pseudoautosomal region (PAR1) of the X and Y chromosomes.

a.	Is the SHOX allele that causes LWD dominant or recessive? Explain. (Note: Sex reversal is not involved.)
b.	Even though SHOX is located on the X chromosome, the pedigree is atypical for an X-linked allele. What features of the pedigree are incompatible with X-linkage?
c.	For each affected individual in the pedigree, determine whether the SHOX disease allele is on the X or the Y.
d.	Explain the inheritance pattern of the SHOX disease allele and the SHOX+ normal allele in pedigree.
e.	Diagram the crossover event that generated the Y chromosome in individual III-5. Your diagram should indicate the positions of the SHOX (disease) and SHOX (normal) alleles on the X and Y chromosomes in the germ-line cells of individual II-3, and SRY on Y.