Blood glucose levels of mice from five strains were measured. The results showed that each strain was different from the others for genes affecting blood glucose level, although the strain differences were small.

Within strains, the chief sources of variation were sex differences, differences between mice from different litters of the same mother, and between mice assayed in different months. Repeatability of measurements on individual mice was low. Genetic analysis, even by biometrical techniques, was not possible because the small genetic effects were obscured by variation due to other causes.

The gene for resistance to phage BF23 and colicins E1, E2 and E3, bfe, was mapped by a combination of conjugation and transduction crosses. Co-transduction of bfe was found with markers in the region between 76 and 79 min on the Escherichia coli genetic map. The highest frequency of co-transduction was found with argH (47%). Three-factor transductional crosses showed unambiguously that bfe lies between argH and supM, at about 77·5 min on the map.

Spontaneously cycling LT/Sv strain female mice were mated to hemizygous Rb(X.2)2Ad males in order to facilitate the distinction of the paternal X chromosome, and the pregnant females were autopsied at about midday on the tenth day of gestation. Out of a total of 222 analysable embryos recovered, 165 (74·3%) were diploid and 57 (25·7%) were triploid. Of the triploids, 26 had an XXY and 31 an XXX sex chromosome constitution. Both embryonic and extra-embryonic tissue samples from the triploids were analysed cytogenetically by G-banding and by the Kanda technique to investigate their X-inactivation pattern. The yolk sac samples were separated enzymatically into their endodermally-derived and mesodermally-derived components, and these were similarly analysed, as were similar samples from a selection of control XmXp diploid embryos. In the case of the XmXmY digynic triploid embryos, a single darkly-staining Xm chromosome was observed in 485 (82·9%) out of 585, 304 (73·3%) out of 415, and 165 (44·7%) out of 369 metaphases from the embryonic, yolk sac mesodermally-derived and yolk sac endodermally-derived tissues, respectively. The absence of a darkly staining X-chromosome in the other metaphase spreads could either indicate that both X-chromosomes present were active, or that the Kanda technique had failed to differentially stain the inactive X-chromosome(s) present. In the case of the XmXmXp digynic triploid embryos, virtually all of the tissues analysed comprised two distinct cell lineages, namely those with two darkly-staining X-chromosomes, and those with a single darkly staining X-chromosome. Four X-inactivation patterns were consequently observed in this group, namely, (XmXp)Xm, (XmXm)Xp, (Xm)XmXp and XmXm(Xp) in which the inactive X is enclosed in parentheses. The incidence of these various classes varied among the tissues analysed. There was, however, a clear pattern of non-random selective paternal X-inactivation in yolk sac endodermally-derived samples which possessed two inactive X-chromosomes. This finding contrasts with the situation observed in the yolk sac mesodermally-derived and embryonic samples which possessed two inactive X-chromosomes, where the ratio of (XmXm)Xp:Xm(XmXp) was 1:1·20 and 1:1·03, respectively, being clear evidence that random X-inactivation had occurred in these tissues.

The mutant phenotype Abnormal abdomen is under the control of a major gene, A53g located distally on the X chromosome. The phenotypic abnormalities are a result of the developmental interaction between this major gene and a modifier system associated with the residual genotype. The primary developmental effect of this mutant genotype is an interference with adult histoblast differentiation resulting in a raggedness or loss of tergite material due to the changes in the formation of the adult abdominal hypoderm. A secondary effect is an interference with middorsal fusion of the histoblasts.

The developmental effect of the genotype is influenced by a number of factors which include crowding, humidity, temperature, and the age of the culture. The mutant phenotype is due to an interaction of the major gene and the modifier system in association with these environmental factors. Gene action in relation to the final phenotype is postulated to be a two-step affair. The first is an increase in protein synthesis under the influence of the modifier system; and the second is the reaction of the histoblast, under the influence of the major gene, to this increase in protein synthesis during its differentiation into adult hypoderm. The function of the environment in this sequence of developmental reactions is postulated to be in its control of the utilization of the increased protein associated with the action of the enhancer genes. This hypothesis is discussed in terms of (1) the production and utilization of gene products and of (2) the regulation of development in terms of this production and utilization in a balanced developmental system.

The white locus is inactivated in a cell-by-cell variegated pattern when juxtaposed with the proximal or distal parts of the nucleolus organizer region (NO) by X chromosome inversion. Recombinants for two such inversions, wm51b and wm4, were obtained and randomized for genetic background. White locus activity was much higher in the wm4 recombinant duplicated for most of the NO and much lower in the wm51b recombinant deficient for it. Although there may be other molecular differences between the heterochromatic regions of the recombinants, the most obvious is the dosage of NO. Suppression of a NO region-evoked variegated phenotype by additional NO doses is discussed in relation to four different classes of models for position-effect variegation (PEV): chromatin structure, nuclear geometry, incomplete transposition of mobile elements, and heterochromatin promoter-driven transcription. A corollary of the structural model is functional subdivision of heterochromatin, which would enable the use of PEV as a tool for its study.

The p6H, p25H, and pbs alleles at the pink-eyed dilution locus in mice (Mus musculus) cause sterility in males and semi-fertility in females when homozygous, while the pd, pun, p, and + alleles do not reduce fertility. Pituitaries from sterile males had significantly lower proportions of gonadotropic cells than pituitaries from fertile males. Ovaries from semi-fertile females contained large numbers of developing follicles, but no corpora lutea or corpora hemorrhagica were found. The proportion of polyovular follicles in ovaries of semifertile females was abnormally high.

Pituitary gonadotropins appear to be reduced in the sterile genotypes although the lesion cannot be localized. Possible relationships between these and other pleiotropic effects of mutant p-alleles are discussed.

There are instances, the most typical being inversion polymorphism in Drosophila, where the genotype is not directly accessible in the adult organism, but can be observed in young life-stages. In these cases, if we want to estimate genotypic probabilities in adult populations, we must examine an offspring sample from adults. In this paper we derive the maximum likelihood estimators, and their errors, for genotypic probabilities in an adult population, according to a standard protocol in which collected parents of a random sample are individually crossed with individuals of a laboratory stock with known homozygous genotype, and a fixed number of their offspring is genetically examined in young life-stages. Arnold's probabilistic model for one locus with two alleles is developed for our estimates. An optimum design which generates a minimum variance is proposed, consisting of examining a moderate offspring number (3–4) per parent. Finally, we propose maximum likelihood estimates when several samples with different numbers of parents per sample, and/or examined progeny per parent are obtained.

Chi is a sequence of eight nucleotide pairs which stimulate recBC-mediated recombination (Smith, 1983a, b). The effect of two linked Chis on recBC-mediated recombination was tested in bacteriophage lambda. It was noticed that the Chi element located on the right side of the phage chromosome is epistatic on the other Chi. These findings support a model proposed by Stahl et al. (1983) which suggests that the recombination machinery moves unidirectionaly in the phage chromosome from right to left. The results also suggest that in the presence of more than one Chi only the rightmost one stimulates recombination.

Adult females from 19 strains of mice were injected with either coumarin or 7-ethoxycoumarin and the urinary excretion of the umbelliferone produced by the metabolism of these substances was measured. With the exception of C57L the strains fell into three classes as follows: high metabolizers (DBA/1 and DBA/2), medium metabolizers (CBA, 129/Rr, NZB and NZW) and low metabolizers (the other 12 strains). The difference in metabolizing ability between the medium group and the low group of strains was also evident when the 4-methyl derivatives of the same two substances were used. However with the 4-methyl derivatives there was no difference in metabolizing ability between the medium group and the high group. The results are interpreted as evidence that the gene Coh on chromosome 7 comprises two closely linked genes which determine cytochrome P-450 isozymes with different substrate specificities.

The importance of atherosclerosis in public health has generated a vast literature relating to epidemiology of the disease, clinical descriptions of symptoms and records of variation of serum concentration of cholesterol, triglyceride or lipo-protein fractions in normal or affected persons. Such evidence has led to a number of hypotheses as to the origins of the disease, and although rival theories may be espoused with fervour or may fluctuate in popularity, a familial predisposition to coronary disease is a recurring theme. In this brief review, which does not aim to be exhaustive and is not concerned with hypertension, we shall focus attention on the more important aspects and attempt to set the conflicting evidence in perspective.

In plant species, typical gene mapping strategies use populations initiated from crosses between two inbred lines. However, schemes including more than two parents could be used. In this paper, a new approach is introduced which uses a four-way cross population derived from four inbred lines. The four-way cross design for mapping quantitative trait loci (QTLs) provides tests for QTL segregation in four lines simultaneously in one experiment. Therefore, it is a more economical strategy than oneusing line crosses between only two lines. The new strategy also increases the probability of detecting QTLs if they segregate in one line cross but not in the other. A multiple linear regression analysis is used for QTL detection. It is proven that the expected residual variance from the regression analysis differs from the pure environmental variance. Correction for the bias is proposed and verified by computer simulations.

1. Nude is a new recessive gene causing hairlessness in the mouse. It is linked to rex and trembler in linkage group VII. The order of the three loci and the recombination frequencies are as follows:

2. In addition to hairlessness the new gene causes reduced body growth rate, very low fertility and a liver disease causing death. Nude mice may be classified at birth by the absence of vibrissae.

3. The hairlessness is due to abnormal keratinization of hair in the follicles. The skin histology resembles that of naked mice. The hair follicles were found to be deficient in free sulphydryl groups.

4. The majority of nude mice die of general body weakness within 2 weeks of birth. The survivors grow slowly and may live for a considerable period. But all nude mice eventually die, usually between 3 and 14 weeks of age.

5. The livers of dead or moribund nude mice are covered with lesions and scars. The defect has been traced histologically to its initial stage, namely, necrosis of small areas of tissue.

6. Attempts to relate the deficiency of sulphydryl groups in the hair follicles to abnormal sulphur metabolism in the liver were unsuccessful.

7. Pseudo-cysts of a parasitic protozoan, Toxoplasma gondii, were identified in the liver and brain of nude mice. In one case the free form of the organism was found.

8. The possible relationship between the liver disease and the pathogenic organism is discussed.

Recombination between two mouse t–haplotypes, tw12tf and tLub-1, was investigated by screening the tailless progeny of the cross ♀ tw12tf/tLub-1 + × ♂Ttf/+tf for the segregation of tufted phenotype, tw12 and tLub-1 lethal factors, and metacentric chromosome (since tLub-l haplotype is associated with a Robertsonian fusion involving chromosomes 4 and 17). The results give a 17% estimate of the recombination frequency between centromere and tf, with tLub-l lethal factor mapping about two-thirds of the distance from centromere to tf and the tw12 lethal factor behaving as if closely linked to tf. This further extends the findings of Silver & Artzt (1981) and of Artzt, McCormick & Bennett (1982), and shows that two t–haplotypes with quite independent laboratory histories recombine at a normal level, supporting the notion that all t–haplotypes basically share the same structure.