|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2004
Publication Date: 3/1/2005
Citation: Van Vleck, L.D., Hanford, K.J., Snowder, G.D. 2005. Lack of evidence for cytoplasmic effects for four traits of polypay sheep. Journal of Animal Science 83:552-556. Interpretive Summary: Inheritance of genetic material is generally about equal from both parents. A major exception is that genetic material in the cytoplasm (rather than the nucleus) is passed directly from the female parent. Thus, if genetic material in the cytoplasm is different in some females and if those differences contribute to differences in economic traits, then selection for those traits would need to consider cytoplasmic effects either directly or indirectly to improve genetic evaluation for direct genetic effects. This study of about 11,000 birth and weaning weight records and of about 7,700 fleece weight and number born per litter records of Polypay sheep was to determine if cytoplasmic genetic effects are important enough to require inclusion in a selection or genetic evaluation program. The results from analyses that included effects of cytoplasmic origin were clear. No variation in those four traits could be attributed to cytoplasmic effects. Thus cytoplasmic effects need not be considered in selection or evaluation of these weight, fleece, and reproductive traits.
Technical Abstract: Analyses of birth and weaning weights, fleece weights of ewes and number born per litter of Polypay sheep collected at the U.S. Sheep Experimental Station from 1978 through 1998, confirmed previous analyses of three other dual purpose breeds that cytoplasmic effects do not contribute to variation in these four traits. In general, estimates of genetic parameters that would be needed for national genetic evaluation were similar to estimates for Columbia, Rambouillet, and Targhee sheep, although Polypay estimates of direct heritability were somewhat less for birth weight, slightly greater for weaning weight, significantly greater for fleece weight, and the same for number born as for the other three breeds. For birth weight only, evidence was found for important dam by year or dam by number born interactions, which are essentially litter effects, as was found for the other dual-purpose breeds. The numbers of records were 11,896, 11,104, 7,748, and 7,831 for birth and weaning weights, fleece weight, and number born per litter with 255 to 316 sires of animals with records. The number of cytoplasmic lines were 260 and 261 for fleece weight and number born and 861 and 882 for weaning and birth weights.