Academic journal article Genetics

Dissection of the Genetic Architecture of Body Weight in Chicken Reveals the Impact of Epistasis on Domestication Traits

Academic journal article Genetics

Dissection of the Genetic Architecture of Body Weight in Chicken Reveals the Impact of Epistasis on Domestication Traits

Article excerpt

ABSTRACT

In this contribution, we study the genetic mechanisms leading to differences in the observed growth patterns of domesticated White Leghorn chickens and their wild ancestor the red jungle fowl. An epistatic QTL analysis for several body-weight measures from hatch to adulthood confirms earlier findings that polymorphisms at >15 loci contribute to body-weight determination in an F^sub 2^ intercross between these populations and that many loci are involved in complex genetic interactions. Here, we use a new genetic model to decompose the genetic effects of this multilocus epistatic genetic network. The results show how the functional modeling of genetic effects provides new insights into how genetic interactions in a large set of loci jointly contribute to phenotypic expression. By exploring the functional effects of QTL alleles, we show that some alleles can display temporal shifts in the expression of genetic effects due to their dependencies on the genetic background. Our results demonstrate that the effects of many genes are dependent on genetic interactions with other loci and how their involvement in the domestication process relies on these interactions.

UNDERSTANDING the impact of epistasis on the evolution of multifactorial traits remains a major challenge in complex-trait genetics. Epistasis is more complicated to model, detect, and interpret than marginal (i.e., additive and dominance) genetic effects since the effect of specific alleles at a locus depends on allelic frequencies at other loci. In a population under natural or artificial selection, allele frequencies will change over time and, as a result of this, so will the genetic effects. Explorations of the impact of genetic interactions on phenotypic evolution thus rely on the study of populations in which both genetic and phenotypic information is available. This requires models that are able todecouple the effect ofgenetic interactions on the displayed genetic variance and to estimate the effect of allele substitutions in different genetic backgrounds.

Domestication of animals and plants provides outstanding examples of rapid evolution. The genetic architecture (i.e., the number of genes and alleles, as well as the nature of interactions among them) that underlies a trait of agricultural interest determines how fast and how far a domesticated species is able to respond to long-term directional selection (LE ROUZIC et al. 2007; LE ROUZIC and CARLBORG 2008). Dissecting the genetic differences between domesticated strains and the corresponding wild populations is a particularly relevant approach to unravel mechanisms involved in the domestication process. Wild and domestic populations normally display large phenotypic differences for a wide range of traits and as domestication has been a rapid process in an evolutionary perspective, a reasonably low number of major genetic factors are expected to contribute to these differences. As wild and domestic populations for agricultural traits produce viable offspring, quantitative trait loci (QTL) detection is a particularly efficient methodology to dissect the genetic architecture involved in domestication (see, e.g., DOEBLEY et al. 1995 and TANKSLEY et al. 1996 for plants or ANDERSSON et al. 1994 for animals).

The increase in the body weight in farm animals is a good example for which a quantitative trait has been drastically modified during domestication, leading to, e.g., a twofold increase in body size in adult layer-type chickens compared to their wild ancestor. The growth of an animal is a complex process involving the basic genetics of metabolism and health in addition to the general adaptation to a particular environment. Some recent studies aiming to dissect the molecular basis of chicken growth using data from crosses between artificially selected lines or between wild and domesticated strains have found that (i) the genetic architecture of body weight is a polygenic trait (up to 20 loci involved) (CARLBORG et al. …

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