Bezalel is absolutely correct here. If one of a couple has the gene and they have two children, the number of people (two) stays the same, and the number of carriers (statistically one) stays the same. If they have four children, the carrier rate is still 50%, just like the parents were. No change.
The only way to reduce carrier rates is for carriers to marry each other. Their affected children take two defective genes out of the pool since they do not have children themselves.
Since Dor Yesharim thankfully does not allow for affected children, none of the defective genes in the population at large is eliminated from the gene pool.
A well known scientist and talmid chochom has developed a mathematical model on the assumption that no carriers marry. It has shown that the carrier rate rises over time, but so slowly that for hundreds of years it has virtually no implications for public policy or private behavior.