Practice question

Recessive lethal alleles cause developmental failure or embryonic death when homozygous, such as homozygous amorphic mutation, but heterozygotes survive because single wild-type allele provides sufficient function, showing haplosufficiency. Selection cannot remove lethal allele efficiently when rare because vast majority of copies hidden in heterozygote carriers escape phenotypic exposure. Random mating populations maintain allele through carriers, each carrier cross producing 25% lethal homozygotes eliminated each generation but replenished. Inbreeding increases homozygosity, revealing lethals and causing reduced fitness, explaining persistence despite severe deleterious effect.