Abstract
The development of Mendelian Genetics shortly after 1900 led to the view that inbreeding decline in plant and animal populations was due to an increasing frequency of deleterious recessive mutants in the homozygous state. It was further speculated that by developing a number of inbred lines, segregation in hereditary differences among the lines would result. However, animal breeding theory remained largely rudimentary and the experiments elementary until a series of classic papers by Sewall Wright on quantitative genetic theory (Wright, 1921, 1922) were published. Wright's papers did much to stimulate inbreeding studies with swine at various agricultural experiment stations. At the Iowa station, Lush (Lush et al., 1948) interpreted Wright's theories to indicate that a balance might be achieved whereby the simultaneous, conflicting effects of inbreeding and selection might cancel each other, permitting the slow attainment of genetic homozygosity without a deterioration of phenotype. To test this, an experiment was started in 1930 in which responses to maximum possible intraline selection under regimes of intense, mild and very slight inbreeding were compared. Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science