Report MDR1 - can we eradicate? in Health and Genetics Posted May 3, 2018 If carriers of a recessive gene are unaffected then the gene pool size argument is a valid one imo. Testing, and carefull breeding can manage. But if, as Journey her argues, heterozygote carriers of this particular gene can be seriously affected, then responsible breeding means doing everything to eradicate it. And that means not breeding carriers.