Genetic diversity and population structure in lines of chickens divergently selected for high and low 8-week body weight

Abstract

A long-term selection experiment for high or low 8-wk BW in White Plymouth Rock chickens was conducted to study effects of selection on BW and correlated characters. Two lines [high (HWS), low (LWS) weight] were established and have undergone 48 generations of selection. The lines were managed to curtail inbreeding and to maintain similar population structures; such is necessary for equitable comparison of selection response between lines. Our objective was to test the success of that breeding strategy by characterizing genetic diversity and inbreeding in these lines. A pedigree of 5,998 individuals was assembled, with 68 founders, 2,962 HWS chickens, and 2,968 LWS chickens. Inbreeding coefficients (F) were calculated for each line. Maximum F was 0.53 and 0.61, mean F was 0.26 (SD 0.15) and 0.30 (SD 0.17), and change in F was 1.3 and 1.6% per generation in LWS and HWS lines, respectively. The effective population size was 38.3 in LWS and 32.1 in HWS lines. The effective number of founders was 15.7 in both lines, and the effective number of ancestors was 17.5 and 15.5 in LWS and HWS lines, respectively. Thirty ancestors accounted for 90% of the genetic makeup of both lines. Seven male and eight female founders still contributed to both lines at generation 48, although some contributed more to one line than the other. Family sizes were similar for males and females of each line, with males having larger family sizes with greater variance. Accumulated inbreeding was high and effective population size was low, as expected in closed lines. Effective number of founders was relatively low compared with actual number of founders, indicating some contributed more than others to the last generation. Family size statistics indicated that fewer males than females were used, leading to the observed levels of inbreeding. Given their similarity in genetic diversity and family size, it can be concluded that breeding decisions throughout the project resulted in similar population structures in the lines.

Reproductive soundness is higher in chickens selected for low as compared with high antibody response

“…The IC line was established from reciprocal crosses of the 41st generation of high and low BW selection lines of White Plymouth Rock chickens (Siegel, 1962;Dunnington and Siegel, 1996;Márquez et al, 2010). The chickens used in this study were progeny of the 12th generation of the IC line.…”

Standing genetic variation as a major contributor to adaptation in the Virginia chicken lines selection experiment

“…The genetic variation entering the population thus represents a sample of the polymorphisms present when these partially inbred lines were founded. Since the founder population was established, the high (HWS) and low (LWS) bodyweight lines have been bred with one new generation per year by single-trait, bi-directional selection for 56-day body weight [10][11][12]. The response to selection has progressed steadily throughout the experiment, resulting in an eight-fold difference in 56-day body weight after 40 generations of selection and currently, in the 57th generation, there is a 16-fold difference between the lines (Fig.…”

Modelling of genetic interactions improves prediction of hybrid patterns – a case study in domestic fowl

“…(i) Animal populations (a) The Virginia (HighrLow) body weight-selected line intercross An F 2 intercross was generated by reciprocal intercrossing of birds from two divergently selected lines of chickens obtained by bi-directional selection for body weight at 56 days of age (referred to as the ' high ' and ' low ' body weight selected lines, Dunnington & Siegel, 1996;Marquez et al, 2010). The lines originate from a common base population, consisting of crosses of seven partially inbred lines of White Plymouth Rock chickens.…”

“…Here, we address this topic using QTL mapping data for body weight from two independent chicken intercross populations. The first population is a cross between two lines artificially selected for low and high body weight at 56 days of age (BW56) (Dunnington & Siegel, 1996 ;Marquez et al, 2010). The second population is a cross between the wild ancestor of the domesticated chicken (Red Junglefowl) and a White Leghorn line selected for egg production, where both early (46 days, BW46) and late (200 days, BW200) body weights were available.…”