Browsing by Author "Dr. Eugene Eisen, Committee Member"

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    Fine Mapping Quantitative Trait Loci Affecting Health and Reproduction in US Holstein Cattle on Chromosome 18
    (2005-08-04) Muncie, Sarah Alissa; Dr. Dahlia Nielsen, Committee Member; Dr. Eugene Eisen, Committee Member; Dr. Melissa Ashwell, Committee Chair
    Continued genetic improvement for milk production has been associated with decreased fertility in US Holstein cattle. A previous study (Ashwell et al., 2004) identified a putative quantitative trait locus (QTL) affecting daughter pregnancy rate at 54 cM on chromosome 18 in one Holstein grandsire family. The goal of this research is to determine the validity of the putative QTL using additional markers and an extended pedigree. Thirteen microsatellite markers located throughout the chromosome were genotyped in 973 animals that were descendants of the original grandsire in which the QTL was identified. Sons of the grandsire as well as six grandson and six great-grandson families of the original grandsire were selected for this study (range of 16 to 169 sons per family). In analysis of the sons using QTL Express, the same putative QTL affecting daughter pregnancy rate was detected and placed at 45 cM. In a joint analysis of thirteen of the largest families, each containing 10 or more sons, a significant QTL for daughter pregnancy rate was detected at 27 cM. QTL affecting daughter pregnancy rate was detected in two additional sub-families (Family II-5 and Family III-2), indicating a putative QTL affecting daughter pregnancy rate is most likely segregating within this pedigree. Across-family analysis also detected putative QTL on chromosome 18 affecting productive life at 35 cM, somatic cell score at 33 cM and percent difficult births at 72 cM. Analysis of individual families identified eight significant putative QTL and six suggestive putative QTL at the chromosome-wise level affecting somatic cell score, productive life, calving ease, percent difficult births, milk yield, fat yield, protein yield and fat percent. A complex pedigree analysis is underway to make full use of statistical power to refine the QTL region affecting fertility. Further verification of the QTL effects identified in this study will allow identification of positional candidate genes to be applied in marker assisted breeding programs.
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    Genetic and Cellular Effects In Mice Selected For Age-Specific Growth
    (2006-08-10) Funk-Keenan, Jhondra; Zhao-Bang Zeng, Committee Member; Dr. Eugene Eisen, Committee Member; Dr. William Atchley, Committee Chair; Dr. Trudy Mackay, Committee Member
    The purpose of this research is to better characterize the origin and evolution of mammalian development. This topic is addressed by examining maternal effects, temporal genetic effects, and hepatocyte endopolyploidy and their impact on mouse growth. This dissertation starts with a discussion of several well-characterized maternal effects and each effect's influence on offspring's growth, gene expression, reproduction, behavior, and disease incidence, among other traits. The role of maternal effects in the evolution of quantitative traits is discussed, as well as the interaction between maternal effects and genomic imprinting in mammals. Growth during ontogeny is characterized by different cellular mechanisms and may be influenced by different sets of genes acting at different ages. To further investigate the differential genetic control of growth during ontogeny, quantitative trait loci (QTL) analysis was performed to search for chromosomal regions influencing growth in two F2 populations produced from four mouse strains. These four strains are derived from an age-specific restricted index selection project, which has lead to differences in rate of development in body weight, as well as differences in cell number and cell size. Chromosomal regions influencing growth during ontogeny do not overlap between the two populations, suggesting age-specific growth is influenced by different sets of loci, as hypothesized. Epistatic interactions partially overlap between populations, suggesting growth throughout ontogeny shares some aspect of genetic architecture. In some species, evolution in quantitative traits is associated with variation in endopolyploidy, or the generation of polyploid cells by DNA replication without subsequent cell division. Given that variation in endopolyploidy affects phenotypic variation, genetic selection for a quantitative trait could alter onset and extent of mammalian endopolyploidy. Flow cytometry is used to characterize hepatic cellular changes as a correlated response to selection for age-specific growth, using the same four mouse strains described above. Polyploid cell frequency within each line increased as ontogeny progressed, as expected from previous research. Selection for divergence in early growth only temporarily changes liver endopolyploidy. However, selection for hypertrophic growth has lead to significant changes in polyploidy frequency, starting at weaning and continuing into adulthood.