Rflps for Somatotropic Genes Identify Quantitative Trait Loci for Growth in Mice

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RESUMO

Restriction fragment length polymorphisms for somatotropic genes were tested for associations with body weight and postweaning growth rate in mice. Polymorphisms for growth hormone (GH) and insulin-like growth factor 2 (IGF-2) genes were identified in stock population lines which had been subjected to long-term selection for high 42-day body weight (H lines) or randomly mated (FP and C lines). Two F(2) populations of mice (5F(2) and MF(2)) were generated from crosses between a single H line of mice and two unselected control lines and subsequently, two divergently weight selected sublines were generated from each F(2) population. The GH(h) allele which had originally been fixed in three of four H lines and absent from all FP and C lines was found to have a significant (P < 0.01) effect on 42-day weight and postweaning growth rate in the F(2) populations. However, GH(h) was associated with lower 42-day weight in the F(2) populations, suggesting that the positive association between GH(h) and weight in the stock population was unique to the high weight selected genetic background of those lines. In agreement with this, the frequency of GH(h) increased in sublines selected for high 42-day weight and decreased in sublines selected for low 42-day weight. The IGF-2(H5) allele was associated with higher weights in a sex-dependent manner in 5F(2). In the high selected subline derived from 5F(2), a significant increase in the frequency of IGF-2(H5) was observed. Therefore this allele, in contrast to GH(h), appears to be a positive indicator of growth irrespective of genetic background.

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