Practice question

Rare recessive alleles persist at low frequency in population and are usually present heterozygously hidden from selection. Offspring of unrelated parents rarely receive two copies simultaneously because chance both parents carry same rare variant is low. Consanguineous marriages unite individuals sharing recent ancestor, greatly increasing probability both spouses carry identical recessive allele inherited identical by descent. Consequently recessive disease incidence rises markedly in children of consanguineous unions, especially first cousins. This underlies higher prevalence of autosomal recessive disorders in communities practicing frequent cousin marriage and in isolated founder populations.