Effects of reduced variance due to selection in open nucleus breeding systems

Mueller, J. P.; James, J. W.

doi:10.1071/ar9830053

Cited by 19 publications

(12 citation statements)

References 5 publications

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“…The difference between annual genetic gain observed in the nucleus and in the base was −96, − 1, 18 and 11 for G1, G2, G3 and G4, respectively. This result is in agreement with the findings of Mueller and James (1983). They reported that the cumulated gain after 10 generations of selection, in a likely sheep or cattle system, would be overestimated by about 20%.…”

Section: Number Of Generations (G)supporting

confidence: 94%

Genetic gain in open nucleus breeding scheme to improve milk production in Egyptian Buffalo

et al. 2010

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Section: Number Of Generations (G)supporting

confidence: 94%

Genetic gain in open nucleus breeding scheme to improve milk production in Egyptian Buffalo

et al. 2010

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“…The scaling factor 0-8 is included to account approximately for the reduction in genetic variance due to selection, the so-called 'Bulmer effect' (Bulmer, 1971). Mueller and James (1983) found that allowance for the Bulmer effect reduced predicted gains proportionately by around 0-2 for open nucleus schemes, but had very little effect on the optimal design or ranking of alternatives, which justified the use of a simple scaling factor. Mueller and James (1983) found that allowance for the Bulmer effect reduced predicted gains proportionately by around 0-2 for open nucleus schemes, but had very little effect on the optimal design or ranking of alternatives, which justified the use of a simple scaling factor.…”

Section: Methodsmentioning

confidence: 99%

Use of MOET in Merino breeding programmes: a practical and economic appraisal

1996

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Commercial application of multiple ovulation and embryo transfer (MOET) technology will be subject to practical constraints and economic rationalism. This study examines use ofMOET in its most profitable arena: to breed stud rams which will disseminate genetic improvement widely through multiplier studs to commercial flocks. A deterministic prediction is used to evaluate schemes based on an open nucleus MOET group within a Merino parent stud, taking account of genetic merit and inbreeding. Selection is based on clean fleece weight with an assumed heritability of 0-4. Embryos are collected at a rate equivalent to 3-45 live lambs per donor. Benefits of MOET were calculated from the discounted expressions of rams sold, and compared with the costs incurred. As the proportion of the flock born from MOET increases, the rate of genetic gain increases rapidly at first, but diminishing returns are observed. The costs ofMOET increase linearly with the number of lambs produced, so the optimum proportion ofMOET lambs is for practical purposes always less than 100%. Some use of MOET was profitable provided the stud sells sufficient stud rams each year. Sensitivity tests found that other parameters had only a small impact on the optimum level ofMOET. In general however, changes which increased the rate of genetic gain (heritability, flock size) or increased its value (wool price, lower discount rate) increased the optimum number ofMOET lambs. The results should provide guidelines to optimum investment in MOET for the wool industry. An across flock genetic evaluation scheme is probably necessary to motivate this investment.

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“…This is a temporary reduction caused primarily by gametic phase or linkage disequilibrium and is counteracted by free recombination at meiosis (Mendelian sampling), and a balance is reached after a few generations. The magnitude of the decrease in variance due to selection depends on the initial narrow-sense heritability, selection accuracy and intensity (among others Bulmer 1971;Mueller and James 1983b;Wray and Hill 1989;Gomez-Raya and Burnside 1990). Consequently, under strong selection, there will be a substantial decrease both in BP response over the first generations and in the additional gain available from PPs.…”

Section: Effect Of Selection and Mating On Genetic Variancementioning

confidence: 97%

“…In contrast, for situations with low heritability or low selection precision, progress from withinfamily selection is less and relatively more is gained from unbalanced parental contributions (Rosvall and Andersson 1999). However, if family variance is exploited there are large losses in both among-family variance (Bulmer 1971;Mueller and James 1983b;Wray and Hill 1989;Gomez-Raya and Burnside 1990) and within-family variance (Verrier et al 1989(Verrier et al , 1990(Verrier et al , 1991.…”

Section: Realised Production Population Gainmentioning

confidence: 98%

Positive assortative mating with selection restrictions on group coancestry enhances gain while conserving genetic diversity in long-term forest tree breeding

Rosvall

Mullin

2003

Theor Appl Genet

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Selection and mating principles in a closed breeding population (BP) were studied by computer simulation. The BP was advanced, either by random assortment of mates (RAM), or by positive assortative mating (PAM). Selection was done with high precision using clonal testing. Selection considered both genetic gain and gene diversity by "group-merit selection", i.e. selection for breeding value weighted by group coancestry of the selected individuals. A range of weights on group coancestry was applied during selection to vary parent contributions and thereby adjust the balance between gain and diversity. This resulted in a series of scenarios with low to high effective population sizes measured by status effective number. Production populations (PP) were selected only for gain, as a subset of the BP. PAM improved gain in the PP substantially, by increasing the additive variance (i.e. the gain potential) of the BP. This effect was more pronounced under restricted selection when parent contributions to the next generation were more balanced with within-family selection as the extreme, i.e. when a higher status effective number was maintained in the BP. In that case, the additional gain over the BP mean for the clone PP and seed PPs was 32 and 84% higher, respectively, for PAM than for RAM in generation 5. PAM did not reduce gene diversity of the BP but increased inbreeding, and in that way caused a departure from Hardy-Weinberg equilibrium. The effect of inbreeding was eliminated by recombination during the production of seed orchard progeny. Also, for a given level of inbreeding in the seed orchard progeny or in a mixture of genotypes selected for clonal deployment, gain was higher for PAM than for RAM. After including inbreeding depression in the simulation, inbreeding was counteracted by selection, and the enhancement of PAM on production population gain was slightly reduced. In the presence of inbreeding depression the greatest PP gain was achieved at still higher levels of status effective number, i.e. when more gene diversity was conserved in the BP. Thus, the combination of precise selection and PAM resulted in close to maximal short-term PP gain, while conserving maximal gene diversity in the BP.

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Effects of reduced variance due to selection in open nucleus breeding systems

Cited by 19 publications

References 5 publications

Genetic gain in open nucleus breeding scheme to improve milk production in Egyptian Buffalo

Genetic gain in open nucleus breeding scheme to improve milk production in Egyptian Buffalo

Use of MOET in Merino breeding programmes: a practical and economic appraisal

Positive assortative mating with selection restrictions on group coancestry enhances gain while conserving genetic diversity in long-term forest tree breeding

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