Investigation on the existence of major gene responsible for body weight and feed intake using a segregation analysis in a mice population

Recent molecular studies have revealed that many quantitative phenotypes are directed by polygenic and major genes. Recent developments in molecular genetics and statistics have allowed the identification and use of major genes to explain the genetic variation. In this context, segregation analysis is a fast, reliable and inexpensive method that uses only phenotype and pedigree information. The main aim of this thesis study is to examine whether body weight, feed intake and feed efficiency in a mouse population are directed by major gene in addition to polygenic and major gene effects by segregation analysis. For this purpose, previously collected dataset was used. 66 F1 were created by crossing 12 M16 and 12 ICR mouse lines. F2 population (n = 661) was formed by F1 selfing. Body weight, feed intake and feed efficiency were measured at 8 weeks. Variance components were estimated by Gibbs sampling. In this study, genetic variance, error variance, major gene variance, additive and dominant gene effects were estimated by segregation analyses. Dominant variance (1.04) was found to be smaller than the additive genetic variance (7.32) for body weight. Polygenic variance (σu2 = 4.46) was found to be smaller than the major gene variance (σG2 = 44.21) with major gene frequencies of p = 0.47 and q =0.53. Polygenic and major gene heritability predicted as =0.29 (± 0.63) and 0.81 (± 0.98) respectively. Dominant effect (24.88) was found to be smaller than additive gene effect (28.80) for feed intake. Polygenic variance (σu2 = 132.29) was found to be smaller than the major gene variance (σG2 = 919.99) with major gene frequencies of p = 0.38 and q =0.62. Polygenic and major gene heritability predicted as =0.35 (± 0.63) and 0.96 (± 0.98) respectively. Dominant effect (-0.00347) was found to be smaller than additive gene effect (0.05073) for feed efficiency. Polygenic variance (σu2 = 0.00017) was found to be smaller than the major gene variance (σG2 = 0.00221), with major gene frequencies of p = 0.60 and q =0.40. Polygenic and major gene heritability predicted as =0.52 (± 0.63) and 0.81 (± 0.98) respectively. Existence of major gene was determined by examining the highest probability density regions. Although the major gene has been identified for body weight and feed intake, this result is not confirmed by the mendelian transition probabilities. In feed efficiency, it was determined that there is no major gene for feed efficiency.