Two Questions

1) Provide an estimate of h2 for the disorder. Based on this, discuss how much influence selection could have on this trait.
Most forms of OI are inherited dominantly meaning only one copy of the mutant gene is required for the expression of OI. Type I, the mild form of OI, is the most common disorder (about 4-5 people out of 100,000 people are affected). In type I OI, the mutation produces normal collagen and mutant collagen because the normal allele (from a normal parent) produces normal collagen and the mutant allele (from an OI parent) produces mutant collagen. Consequently, normal collagen combined with mutant collagen produces a mild form of OI. The most severe form of OI is type II in which only mutant collagen is produced; as a result, bones that are made become brittle. h² shows the amount of genetic variation that is due to additive effect. Since OI is a genetic disorder, h² should be high. The equation, R=h²S, shows that selection has a strong influence on this trait because the mutation reduces the fitness of the person with this disorder.

2) What effect might inbreeding have on this disorder?

Inbreeding increases homozygosity and decreases heterozygosity. Therefore, inbreeding will result in individuals with severe OI (Type II) or no OI (normal) and no mild forms of OI (Type I). The frequency of OI (Type II) in the population will increase and Type I (heterozygous genotype) will decrease.

http://ghr.nlm.nih.gov/condition=osteogenesisimperfecta