Effects of radiation on selection progress in mice Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/d791sk462

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  • The effects of x-irradiation on quantitative genetic traits was investigated by comparing the response of irradiated mice to selection for litter size and 28-day weight with the response to selection for the same two traits in non-irradiated lines. Irradiated lines were maintained at three levels of x-irradiation, 25 r, 50 r and 100 r, administered to both males and females immediately before pairing. No matings were made later than 14 days after irradiation so that only the effects of x-irradiation upon the post-meiotic stages of gametogenesis were studied. The lines receiving 50 r and 100 r were all lost by the fourth generation of selection. An interaction of genetic and physiological factors was assumed to be responsible for the reduced fertility leading to the termination of these lines. Selection response for litter size was negative in five of the six irradiated lines. This was attributed to reduced selection differentials due to lower fertility and to reduced heritabillty due to physiological masking of the additive genes for litter size. It appears that the accumulation of recessive lethals also may have played a role in reducing heritability in the irradiated lines. Selection response for 28-day weight was positive in four of the six irradiated lines, although less than in the non-irradiated controls in most cases. Three of the irradiated lines had realized heritability values greater than either of the controls. Some increase in usable genetic variance for 29-day weight was indicated although reduced selection differentials prohibited increased selection response. Irradiation of females in metestrus or one day after metestrus increased the size of their litters. Females mating later than one week after irradiation produced fewer litters and litters of smaller size than control females. Most of the fertility problems encountered in irradiated animals could be attributed to the females. Histological examination eight months post-irradiation revealed serious radiation damage in ovaries while spermatogenesis appeared normal. Females receiving 50 r and 100 r had a significantly higher incidence of mammary gland tumors at ten months of age than the non-irradiated controls.
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