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INBREEDING WITH THE HOMOZYGOTES AT A DISADVANTAGE
Author(s) -
REEVE E. C. R.
Publication year - 1955
Publication title -
annals of human genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.537
H-Index - 77
eISSN - 1469-1809
pISSN - 0003-4800
DOI - 10.1111/j.1469-1809.1955.tb01357.x
Subject(s) - inbreeding , selfing , mating , biology , genetics , fertility , inbreeding depression , cousin , selection (genetic algorithm) , population , demography , history , archaeology , artificial intelligence , sociology , computer science
Summary The rate of progress towards homozygosity is calculated for various selection pressures against homozygosity at a given locus, when systematic inbreeding is carried out by selfing, sib mating, half‐sib mating in which a male is mated to two of his half‐sisters who are full sisters, and double first‐cousin mating, under the condition that selection is only allowed to act within lines, i.e. there is no tendency to replace more homozygous by less homozygous lines because of the greater fertility, etc., of the latter. The systems of inbreeding considered require respectively 1, 2, 3 and 4 parents per generation per line. If the homozygotes aa and bb both have survival value s , compared with 1 for ah , then for all finite a homozygosity is eventually achieved, but as a is reduced there is a greater relative slowing down of progress in the milder than in the more intense forms of inbreeding, e.g. when s is reduced from 1 to 0–2 the number of generations required to make a given amount of progress is multiplied by 3–8 for selfing, by 14 for sib mating, by 30 for half‐sib mating, and by 142 for double first‐cousin mating. The solution is also given for various survival values of aa when bb is lethal. Making bb lethal instead of equal in fitness to aa speeds up the rate of progress when the survival value of aa is greater than about 90% for sib mating, 40% for half‐sib mating and 20% for double first‐cousin mating. In the case of sib mating, when aa and bb have survival values s 1 and s 2 , then it appears that for any fixed Sj the rate of progress has a minimum for a value of s 2 less than s 1 . It is assumed that the same applies to half‐sib and double first‐cousin mating. Taken in conjunction with Hayman & Mather's analysis of the effects of inbreeding when selection against homozygosis occurs between lines as well as within lines, it appears that inbreeding to obtain homozygosity should be carried out so as to minimize selection between lines and also as intensely as possible. The latter conclusion may need qualifying if interaction between homozygous loci causes a large proportion of the possible homozygous genotypes to be in viable.