Genetics - Theses
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ItemStudies on minor non-metrical skeletal variants in the mouse and man(University of Melbourne, 1970)This thesis consists of papers presenting the results of studies on the genetical, developmental and anthropological aspects of minor non-metric al variants in man and the house mouse. The work is mainly on variants of the skeleton, particularly the cranium, but includes a limited discussion of published data on minor non-metrical variants of the muscular and vascular systems. Each study is based on a number of variants, and, where applicable, single measures have been obtained to express the overall difference in skeletal variability between populations or the overall effect on skeletal variability of certain environmental factors. Investigations into the role of genotype and environment in the determination of minor skeletal variants in mice and man indicate that most of them are under some genetic control but that maternal physiology and other non-genetic factors may influence the frequency of individual variants. Data presented here (Publication 1) on 25 minor skeletal variants in inbred strains of mice and their hybrids suggest that genotype is more important than environment in determining skeletal variability. Although the frequency of a few individual variants was found to be significantly affected by certain non-genetic factors, when many variants were considered together the environment had no overall significant effect. In contrast, large differences, due mainly to genetic factors, were observed between inbred strains and hybrids. Further studies on inbred strains of mice and hybrids (Publication 2) indicate that stabilizing mechanisms operate during the formation of the skeleton. For most of the 29 bilateral minor non-metrical variants studied , the frequency of asymmetrical mice (i.e., those with the variant present on only one side) was less than expected on the assumption that the number of mice with the variant present on both, one or neither sides depends solely on the frequency of the variant on each side. This tendency for the development of the skeleton to be canalized against asymmetry has been described as a form of morphogenetic homeostasis. The same phenomenon has been observed for bilateral minor non-metrical variants in man (Publication 3) for the skeletal, muscular and vascular systems (based on data published by Danforth in 1924) and for the skeletal system of Australian Aborigines. Studies on inbred strains of mice (e.g., Publication l) indicate that genotype plays the major role in determining the frequency of minor non-metrical variants. If these findings can be extrapolated to man, minor non-metrical variants may be of use in anthropological work. A general survey of skeletal variation, based on 30 such variants, was carried out on Aboriginal crania from many parts of Australia (Publication 4). Regional differences in the pattern of cranial morphology were observed which appear to culminate in two extreme populations: one in the north and north-west of the continent, the other in south-eastern Australia. These results were considered in relation to some current theories on the origin and ethnic composition of the Australian Aborigines.