After tracing the history of Dr. Goodale's selection study of white-spotted mice, it appears that the white spotting selected for was controlled by a complex of genetic factors. Spot occurrence was controlled by a single gene pair, causing small white areas on the forehead. The size of head spot was determined by a few modifier gene loci, among which some nonadditive gene action may have taken place. The B locus appeared to be associated with head-spot size, either through linkage or pleiotropic effects. There may also have been some maternal effects on head-spot size. Selection for increased head-spot size was successful, the heritability of the trait being between 0.1 and 0.2. The increase in spot size was fairly slow; a total score of about 13 units was reached over 16 years of selection. Accumulation of factors favoring increased head-spot size led eventually to the appearance of body spots, and selection began to concentrate on these. Body-spot size was controlled by a larger number of gene pairs; gene action appeared to be more nearly additive, and there appeared to be no maternal effect or association with B locus alleles. Heritability of body-spot size was 0.3 to 0.5. Total score increased from 13 to 56 units over the 11 years of selection.

Animals↗

PubMedDate not supplied

Effect of maternal parity on aneuploidy in early mouse embryos.

An attempt to evaluate the incidence of chromosomal aneuploidy in mouse blastocysts recovered from females of various ages and parity levels revealed an insignificant regression coefficient for aneuploidy on age of the female and its square, and an insignificant correlation coefficient for aneuploidy with the number of previous offspring born to the dam. However, significant regression coefficients were obtained for aneuploidy on parity of the dam and its square. These results indicate that not only does aneuploidy increase with parity level, but the rate of increase accelerates as parity level increases. Possible explanations for the increase in aneuploidy and its detrimental effect on reproductive efficiency were discussed.

Aneuploidy↗

PubMedDate not supplied

Myelin deficient, a new neurological mutant in the mouse.

A new autosomal recessive gene in mice is described that produces deficiencies in central nervous system myelin and quaking or trembling of the hindquarters during locomotion. Although both behavioral and central nervous system abnormalities resembled those produced by qk, the new mutation was not an allele of qk. We propose that the new mutation should be labeled myelin deficient (symbol, mld).

Alleles↗

PubMedDate not supplied

Crossing selected lines vs. selecting from a cross in mice.

Eight generations of selection were practiced for post-weaning gain in body weight and for litter size at birth in two outbred stocks of mice and in a stock derived by crossing these outbreds. At each generation, the selected outbred stocks were crossed, and offspring of the cross compared to those from selection in the cross stock. Selection from the cross stock gave greater response than crossing selected stocks in post-weaning gain, a trait where inheritance was primarily by additive gene action. For litter size, a trait where dominance and epistatic interactions were of greater importance, no clear advantage resulted from crossing prior to selection.

Animal Husbandry↗