The chromosomal localization of the mouse gene coding for desmin, one of the muscle-specific intermediate filament subunits, was determined by in situ hybridization using a specific 3H-labelled DNA probe. There is only one copy of the desmin gene and it is located on chromosome 1 in the band C3. This result adds an eleventh locus to a conserved gene cluster and confirms the partial homology that exists between the long arm of human chromosome 2 and chromosome 1 of the mouse.

Two allelic forms of the supernatant NADP isocitrate dehydrogenase (IDH) are found in inbred strains of mice (Henderson, 1965). The five C3H substrains tested, namely C3H/HeJ, C3H/Re-sl, C3H/N-wJ+, C3H/J-WX+ and C3HeB/FeJ, all proved to be of the Id-la/Id-la genetic constitution. (For the nomenclature of inbred strains and substrains of mice see Staats, Committee on Standardized Nomenclature for Inbred Strains of Mice, Cancer Res. 24 (1964), 147–168.) All these substrains were obtained from E. S. Russell at the Jackson Memorial Laboratory, Bar Harbor, Maine, and were presumably all derived from C3H/He mice.

The effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci with equal effects without dominance was investigated theoretically. Conditions for a stable equilibrium under selection and mutation, in the absence of drift, have been obtained, and hence the amount of genetic variability which can be maintained by mutation has been determined. An approximate expression for the average amount of genetic variability to be expected in the presence of drift in a population of finite size has also been obtained and evaluated.

Mice of two strains, N and C, were used in studies on body-size, pituitary size, and endocrine potency of the pituitary. Strain N had been selected for large (NL) and small (NS) body-size; strain C had also been selected for large body-size (CL) but had been crossed to an outbred strain segregating pituitary dwarfism.

Pituitary weights and body-weights were highly correlated, the regression lines being common in NL and NS mice. Female pituitaries were considerably heavier than male pituitaries in CL mice. In relation to body-weight, CL pituitaries were consistently heavier than those of NL or NS mice.

No differences were detected in the unit potency of gonadotrophins in the pituitaries of NL and NS mice as estimated by the uterine response of immature outbred mice to subcutaneous injections of pituitary tissue. The uptake of 131I into the thyroid was comparable in NL and NS mice per unit of body-weight, and the thyroid secretion rate was also similar using animals of the same body-weight. Immature mice of both lines responded by increased growth to injections of growth hormone or fresh mouse pituitary, though the response was greater in NS than in NL mice.

The primary response to selection has probably been in the size of the pituitary rather than in its unit potency. The interrelationships between body-size, body components, organ size and endocrine levels are discussed.

We have utilized isoelectrofocusing two-dimensional polyacrylamide gel electrophoresis (IEF-ID-PAGE) to determine the frequency of variant proteins detected in mouse testes, and to examine an inbred strain with spermatogenic abnormalities. The observed frequency of variants, 4·2 ± 1·0%, is comparable to results reported for liver. A variant for a protein, identified as tubulin by immunoblotting, was observed in an inbred strain (PL/J) which has defective spermatogenesis, but was also observed in another inbred strain without spermatogenic defects. The gene symbol Tbn is proposed for this β-tubulin locus.

Large reciprocal differences in recombination frequencies were observed in F1 female progeny of a number of strain crosses. These reciprocal effects on recombination were found in several intervals of all three major chromosomes; they were greatest in intervals proximal to or spanning the centromere but were also found in some distal regions. The direction of recombination change was not consistent over different chromosomal intervals. There was no clear trend for reciprocal recombination differences to be associated with change of interference values between adjacent intervals. A close association was found between reciprocal female recombination effects, male recombination and other component traits of hybrid dysgenesis. However, reciprocal differences in female recombination were not restricted to dysgenic crosses. Backcross experiments demonstrated that reciprocal differences in the centromeric region of chromosome III were the result of increased crossing-over in dysgenic F1 hybrids rather than decreased crossing-over in the reciprocal hybrids. It is concluded that genotype-cytoplasm interaction can be a major factor influencing recombination frequencies and that the use of interstrain hybrids for recombination measurement may lead to errors in the estimation of intrastrain frequencies.

Following segregation in two unrelated wheat crosses, albinism was associated with chromosome 7B nullisomy which permitted expression of mutant genes on chromosomes other than 7B. The frequencies of albino segregante differed in the two instances, being dependent upon the morphology of the 7B monosome, which was either telocentric 7BL or normal.

A viridis phenotype also segregated from one cross. Its expression was independent of 7B aneuploidy. Failure to obtain lines segregating only for green and viridis phenotypes was due to semi-lethality resulting from the presence of two 7B isochromosomes.

Robertson, 1978, addressed the interesting problem of ascertaining the distribution of the time to detection of a recessive homozygote in a finite population. He was motivated in part by breeding and artificial selection practices. The same problem arises in the context of evolutionary processes and medical genetics since it refers to the time of first appearance as a homozygote of a new crossover event or a mutant gene.

Crosses between various types of mutant giving specific patterns of aberrant segregation were performed in the b2 spore colour locus of Ascobolus immersus. The map of 41 mutations showing various patterns of aberrant segregation was established. The frequency of wild-type recombinants and the map additivity, map expansion and map contraction characteristics were shown to be strongly dependent upon the pattern of aberrant segregation of the mutations used. Mutations giving no postmeiotic segregation and an excess of conversion to wild type over conversion to mutant exhibit map expansion in small intervals and a strong map contraction in large intervals. Mutations giving postmeiotic segregations also exhibit map contraction in large intervals. Mutations giving no postmeiotic segregations and an excess of conversion to mutant over conversion to wild type show map additivity and thus provide a simple way for devising gene maps. The relationship between the mapping properties and the pattern of aberrant segregations is accounted for when considering parameters of gene conversion: frequency and distribution of hybrid DNA, frequency and direction of mismatch correction.

The shape of the mandible in. nine sublines of C57BL/Gr, seven other strains of ‘C57 ancestry’ and four unrelated strains was studied by multivariate techniques. The generalized distance function was used to classify individuals in the groups which they most closely resembled. The degree of misclassification depended on the pedigree relationship between strains and sublines. The generalized distance between pairs of subline centeroids was also highly correlated (r = 0·60) with the number of generations between them. A canonical variate analysis was used to reduce the dimensionality so that a graphical display of the relationships between strains and sublines could be made. The results agreed closely with the classification analysis. It was concluded that the shape of the mandible could be used for subline identification though the accuracy of this technique depends on how closely the sublines are related.

The effect of fertility differences between homogamous and heterogamous matings are considered. The equilibria are evaluated and their stability deterimined. Completely positive and completely negative assortative mating with two and with three forms, are investigated as special cases of the above fertility structure. In these cases convergence of the genotype frequencies has beer demonstrated.