deleterious mutation

Lande R 1988 Genetics and demography in biological conservation. Science 241:1455-1460.

• roughly half the inbreeding depression is due to individually rare, but collectively abundant, nearly recessive lethal and semi-lethal mutations at about 5000 loci
• individuals in large outbred populations typically are heterozygous for one or a few recessive lethals
• (Simmons & Crow 1977)
• the remaining inbreeding depression in Drosophila is caused by numerous slightly detrimental mutations that are mildly recessive
• it is not generally realized that gradual inbreeding or reduction of population size creates relatively little permanent inbreeding depression since selection tends to purge the population of deleterious recessive alleles when they become homozygous