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‘Midget’, a new dwarfing gene in the house mouse dependant on a genetic background of small body size for its expression

Published online by Cambridge University Press:  14 April 2009

Ruth E. Fowler  and
R. G. Edwards
Ruth E. Fowler
Affiliation:
Institute of Animal Genetics, West Mains Road, Edinburgh 9
R. G. Edwards
Affiliation:
Division of Experimental Biology, National Institute for Medical Research, Mill Hill, London, N.W.7
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Midget, a new dwarfing gene in the house mouse, was found in a line (NS) selected for small body size. Backcrosses to, and heterozygous matings of NS mice gave midget offspring in the expected 1:1 and 1:3 ratios. Backcrosses to two other lines of mice selected for small body size resulted in fewer midget offspring than expected and in a reduced phenotypic expression of the gene, though matings between these midget offspring gave all midget progeny.

A characteristic check in growth occurred between 15 and 21–24 days of age, and midgets rarely exceeded 10 g. at 6 weeks of age. They were 1·2 g. lighter than NS litter-mates at 3 weeks, and 3·6–4·4 g. lighter at 6 weeks. Fostering or transferring 3½-day-old midget embryos to the uteri of large mothers slightly increased the growth-rate, though the characteristic growth check still persisted. Transfer as embryos did not influence the midget phenotype.

Midget males were of near-normal fertility. The females were semi-sterile due to irregularity or absence of oestrous cycles, failure to ovulate, or the death of embryos before implantation. Each of these factors, which were also found in NS mice, could be remedied by the administration of exogenous hormones.

The genetic factors underlying the expression of midget are discussed, and the physiological traits associated with this and with other dwarfing genes are compared.

Type
Research Article
Information
Genetics Research , Volume 2 , Issue 2 , July 1961 , pp. 272 - 282
Copyright
Copyright © Cambridge University Press 1961

References

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