• Donald Michie

      Articles written in Journal of Genetics

    • Genetic and environmental influences on the secondary sex ratio in mice - With one text-figure

      Alma Howard Anne McLaren Donald Michie Gerhard Sander

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      Over 700 litters, comprising some 4500 mice, derived from the sixteen possible types of mating within and between four inbred strains, were sexed at birth, and the parentage, parity and size of each litter was recorded. Except in a preliminary series of within-strain crosses, the first litter of each mating was not recorded.

      There was no significant heterogeneity between the sex ratios of different litters belonging to the same mating type, parity and litter size.

      In the main body of data inbreds and hybrids agreed well in sex ratio, giving a significant excess of males.

      There was close agreement between the results of reciprocal crosses, but highly significant heterogeneity between the sex ratios of the six different hybrid genotypes (reciprocals combined).

      The genetic factors responsible for the differences between hybrid genotypes appear to be those acting directly on the offspring, rather than through the male or female parent.

      By contrast, there was no evidence of heterogeneity between the inbred genotypes. The difference in this respect between inbreds and hybrids was found to be statistically significant and was discussed in the light of the complementary phenomenon, whereby inbred strains are found to show greater within-genotype variability than interstrain hybrids.

      The main series of inbreds had a significantly lower proportion of females and a lower mean litter size than the preliminary series from the same four inbred strains. We conclude that in our mice the female sex was the more sensitive to variations in intrauterine conditions.

      No significant relation was detected between sex ratio and parity.

      In the main body of data a significant rise in the proportion of males with increasing litter size was shown by both inbreds and hybrids. This result was interpreted on the assumption that intra-uterine competition was the overriding factor in foetal death.

      No similar effect was shown by the preliminary series of inbreds. This was attributed to a reduced prenatal mortality associated with the larger mean litter size in this series.

      In the preliminary series of inbreds, first litters did not differ significantly in sex ratio from subsequent litters.

      On the other hand, the four strains were in significant conflict in respect of the relation between sex ratio and litter size revealed in these first litters.

    • Genetical studies with ‘Vestigial Tail’ mice I. The sex difference in crossing-over between vestigial and rex

      Donald Michie

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      A total of 512 mice were classified for both Rex and vestigial in backcross matings in which the two markers were segregating jointly.

      The frequency of recombination in male heterozygotes was estimated as 17-9 ± 2.2%, and in female heterozygotes as 27.3 ± 3.1 %.

      The difference between the sexes is statistically significant at the 2% probability level.

      A review of linkage work in the mouse shows that out of twenty-six intercepts in which some evidence is available eight show a significant sex difference. In six of these it is the female which exhibits the higher frequency of recombination.

      There is no significant evidence of an effect of the age of the segregating parent upon the frequency of recombination between Rex and vestigial.

    • Genetical studies with ‘Vestigial Tail’ mice II. The position of vestigial in the seventh linkage group

      Donald Michie

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      The recessive mutant ‘vestigial tail’ (symbol vt) was found to lie on the same side of Rex as sh-2 in linkage group VII. The frequency of recombination between vt and sh-2 was estimated as 1.7 ± 1.7%, and between vt and wa-2 as 28.0 ± 3.5%.

    • Genetical studies with ‘Vestigial Tail’ mice III. New independence data - With one text-figure

      Donald Michie

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      Data are given on 1107 mice from matings in which the seventh linkage groups marker vt was segregating jointly with sex. The recombination frequency was estimated as 51.64 ±1.94%. This is in poor agreement with the value of about 56% indicated by Wright’s [Mrs M. E. Wallace’s] (1947) data on the recombination of sex and sh-2.

      The frequency of recombination betweenRe and sex was estimated as 51.0 ± 2.9%.

      Independence data were given on an additional 46 pairs of loci.

      The relation of the seventh linkage group to sex was discussed in connexion with various anomalous observations.

      A compilation of significant associations between pairs of unlinked loci was made from published independence data and discussed in the light of the hypothesis of affinity.

    • Genetical studies with ‘vestigial tail’ mice IV. The interaction of vestigial with brachyury - With one text-figure

      Donald Michie

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      The phenotypic effects of combiningSd andun withvt (vestigial tail) are not grossly distinguishable from the effects ofvt alone. On the other hand, mice of the genotypeT/+, vt/vt are tailless and, on a given genetic background, both sexes regularly-show abnormalities of the urogenital and alimentary systems externally recognizable by imperforate anus.

    • Variability of response in experimental animals - A comparison of the reactions of inbred,F1 hybrid and random bred mice to a narcotic drug

      Anne McLaren Donald Michie

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