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  • Leonardo Persson posted an update 7 months, 2 weeks ago

    He deemed practical questions for example the relative accuracy of choice on a cow’s own efficiency vs. that of her progeny imply (Lush1935). Together with his colleague L. N. Hazel, Lush developed choice index principles to produce ideal use in the information. In the plant breeding context, Smith (1936) had derived a discriminant function, i.e., a selection index, and thanks “Fisher for guidance and inspiration. [. . .] section I [. . .] is tiny more than a transcription of his recommendations.” Hazel (1943) introduced the concept of genetic correlations and showed the way to use these to compute multitrait selection indices, and Lush (1947) derived how ideal to weight an index of records on a person and its sibs. He and colleagues recognized also that prices of progress should be maximized per year rather than per generation and deemed the tradeoff involving the high accuracy of a progeny test and the shorter generation time by selecting on own efficiency (Dickerson and Hazel 1944). Lush’s investigation was closely focused on practical problems of short-term improvement, mainly on tips on how to choose the very best ASP2215 web animals to breed the next generation. More than such a time scale of a couple of generations, concerns of finite population size, size of gene effects, and epistasis will not be essential, so Lush could just at the same time be following Fisher as Wright. Further, he discusses in Animal Breeding Plans (Lush 1945, Chap. 11) how selection can change variability abn0000128 in a population: he argues that, despite the fact that the chosen men and women are phenotypically and somewhat genetically much less variable, most will recover variation in subsequent generations, and so an assumption of many loci and of close to constancy of response is a reasonable approximation in the medium term. (This was formalized later by Bulmer, discussed under.) Nevertheless Lush shows the influence of his mentor Wright, who had participated in multigeneration choice experiments for his Ph.D. with Castle and subsequently undertook breeding experiments at U.S. Division of Agriculture (USDA) and analyzed pedigree records of Shorthorn cattle, all of which took him to the shiftingbalance theory (Wright 1931, 1932). Summarizing later: “It was apparent, having said that, from the breeding history of Shorthorn cattle [. . .] that their improvement had truly occurred primarily by the shifting balance process instead of by mere mass selection. There have been usually quite a few herds at any provided time, but only a couple of had been normally perceived as distinctly bmjopen-2015-010112 superior [. . .]. These herds successively made more than the whole breed by becoming principal sources of sires” (Wright 1978, pp. 1198?). Nevertheless in chapter 11, Lush (1945) discusses selection for epistatic effects and presents a twodimensional “peaks of desirability” in addition to a contour diagram of Wright’s adaptive landscape (from Wright 1932). Lush concludes the chapter with practical advice: “Only seldom is mass selection entirely ineffective, as when selection is to get a heterozygote, when choice has already carried the population into steady epistatic peak, or when choice is within an completely homozygous line. Usually, even so, the rate of progress by mass choice is slow and could possibly be produced much more rapid by a judicious use of relatives and progeny or by additional cautious manage from the environment.” Later in the book, after describing how you can raise selection responses, he considersW.

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