Genetic Parameters in Progeny-Test Selection for Field Performance of Strain-Cross Layers

Abstract

Heritabilities, genetic and phenotypic correlations and sire x location interaction were estimated for 14 traits from hierarchial covariance analysis within each of four 5-week hatching periods in 9 years. Numbers averaged 93 sires, each with 61 pullets from 11 or 12 dams of two lines distributed among 5 to 14 single-cage field locations, in each of 36 period-years and totalled 204,235 pullets from 3,354 sires. Inbreedings increased .4 to .1% per year but was uncorrelated with reproductive rate or selection applied. Heritability estimates were very stable over time and between seasons, with empirical SE for means of .4 to 1.6%. Lower heritabilities across than within locations, justify multiple-location progeny tests, especially for egg production, sexual maturity, flightiness, shell defects and blood spots.Genetic correlation (r G ) changed with time only for body weight with production rate (.03 ± .01 per year) and between seasons only for production rate with egg size and shape, with empirical SE of means for r G of .02 to .04. Important antagonistic genetic correlations were those of egg production and sexual maturity with egg size and specific gravity (-.2 to -.4) and of body size with egg size (.4). Corresponding phenotypic correlations were made less antagonistic by favorable environmental correlation. Dam component correlations were made less antagonistic than sire correlations by more favorable correlations for dominance and maternal effects. Favorable genetic correlations increased expected gains from 12-trait index selection less than the unfavorable correlations reduced it. Predicted response in 12-trait breeding value from sire selection was 96% of maximum when only adult mortality, % production, egg size, body size and sexual maturity of progeny were used; addition of excitability and six egg quality items should improve all except specific gravity but reduce progress in egg size.

Life-History Consequences of Divergent Selection on Egg Size in Drosophila melanogaster

“…First, although functionally related, egg size and number might not share the same genetic basis and may therefore evolve independently. This possibility seems remote given that long-term selection on these characters (e.g., in domestic fowl; Emsley et al 1977) apparently produces negative genetic correlations between them. Second, and more likely, there may have been a negative pleiotropic genetic correlation between these two traits, but we were unable to detect it.…”

Life‐History Consequences of Divergent Selection on Egg Size inDrosophila melanogaster

“…There is, however, comparatively little evidence of genetic trade-offs between egg size and fecundity. What evidence there is comes from domestic fowl (chickens and turkeys), which are characterized by a history of selection to maximize both traits (e.g., Emsley et al 1977). Such species are expected to show an antagonistically pleiotropic relationship between egg size and fecundity, because strong selection to maximize both traits would tend to fix alleles leading to high levels of both characters and eliminate those leading to low levels of both characters, leaving only those alleles that contribute positively to one trait and negatively to the other segregating in the population (Roff 1996).…”

Effectiveness of Progeny Test Index Selection for Field Performance of Strain-Cross Layers

“…Genetic correlations and standard deviations were those calculated from these data by Emsley et al (1977) from sire components of variance and covariance for all traits except EMRT and AMRT. The correlations of genotypes and progeny phenotypes were estimated with heritabilities of .029 per EMRT and .066 for AMRT and correlations among fullsibs of .053 for EMRT and .041 for AMRT, along with the appropriate numbers of progeny for each type of progeny average (Lush et al, 1948;Brunson et al, 1955;Dickerson, 1957;Morris, 1959).…”

“…PROCEDURES Selection Procedures. Genetic parameters for several performance traits have been accurately estimated from field records of four strain crosses of White Leghorns by Emsley et al (1977). Actual responses from selection for strain-cross progeny field performance have been estimated by Kashyap et al (1980) for these traits, as well as for mortality, hatchability, and fertility.…”