DY, dor yesharim increases the carrier rate since it minimizes the chance of 2 carriers marrying each other and ending their line. Lets take Tay sachs as an example. Once upon a time in a population where by some estimates 1/25-30 is a carrier for tay sachs some would marry each other and have several of their children die Rch”l taking the “defective” gene with them. Now however virtually all carriers go on to reproduce succesfully, this however (over time)leads to an increase in the gene frequency rate.
statistically half of a carrier’s children will be carriers as well, all will survive. If the carriers dont marry other carriers the carrier rate frequency will increase over time.