
Steroid 21-hydroxylase gene mutations as a result of exchange of sequence between the functional 21-hydroxylase gene (21B) and its closely related pseudogene (21A). The duplicated complement genes (C4A and C4B) and steroid 21-hydroxylase genes (21A and 21B) located on tandem 30-kb repeats are shown. Unequal crossover or unequal sister chromatid exchange results in either formation of a fusion gene or complete deletion of the functional 21-hydroxylase gene.











