1. The earliest manifestations of the gene for syndactylism discovered include hyperplasia of the apical ectodermal ridge of the limbs and hyperplasia of parts of the limb epidermis (10–10½-day stage). Somewhat later, a similar hyperplasia of the epidermis in the distal parts of the tail is found in some sm/sm embryos.

2. Enlargement and deformation of the foot plates in both fore and hind limbs is present in the 12-day stage; in the fore limbs it probably starts on the preceding day. The foot plates are bent over in a palmar or plantar direction respectively; the crowding together of the middle digits thus produced is the mechanical cause of syndactylism.

3. It is suggested that the enlargement of the foot plates with the ensuing deformities is due to increased stimulation of mesenchymal growth by the hyperplastic apical ectodermal ridge. On this interpretation, all the skeletal effects (including those in the tail) are secondary to a systemic tendency to epidermal hyperplasia.

4. The hyperplastic regions of the apical ectodermal ridge and of the limb epidermis start to keratinize (parakeratosis) in the 13-day stage whereas in normal development keratinization of the skin does not start until some 3 days later.

The F factor and the K resistance determinant form an R factor (KF) in E. coli K12. In this R factor the two plasmids are independent of each other and occupy different attachment sites in the host cell.

Treatment of an F+(K) strain with acriflavine and acridine orange yielded the following classes: F+K−; F−K+; and F−K−. The K determinant was thus curable independently of F, which supports the hypothesis of independence of the two plasmids. In Hfr(K) strains, K remains curable with acridines while F is immune. Thus, K remains independent of F in both the F+ and Hfr states.

The use of higher concentrations of acridine orange than those needed for cure of K in the F+(K) strain resulted in no elimination of K, although the F factor was absent from all surviving lines tested. It is suggested that this is caused by equal inhibition of replication of both the chromosome and K, and greater inhibition of that of F.

Maximum likelihood estimation methods with an individual animal model were used to analyse a bi-directional selection experiment, with control, for cannon bone length in Scottish Blackface sheep. A method is described for partitioning the likelihood to allow within- and between-line estimates of genetic variance. It is concluded that both sources of information made substantial contributions to the precision of the base population heritability estimate. The implications for different experimental designs and varying heritability are discussed.

1.Complementation between thirteen proline auxotrophs in A. nidulans was studied. Two groups of mutants with different complementation pattern were found. These two groups could also be distinguished on the basis of recombination tests.

2. The spontaneous reversion rate of proline mutants was established. In all cases studied the reversions were due to suppressor mutations. Dominant, semi-dominant and recessive suppressors were distinguished.

3. Complementation between recessive suppressors was studied. Only a few of the suppressors obtained could be located in different complementation groups.

4. Three suppressor loci were mapped, two of them, su-2 and su-6 in chromosome III linked to the phen-2 locus, respectively 22 and 26 map units distant, and the third in chromosome I, linked to the ad-9 locus (1·9 map units). su-2 is a mutant at the Su-4 pro locus already identified by Forbes (1956).

5. The action of these suppressors is thought to consist in affecting the pathway of arginine synthesis by one of three mechanisms: (1) accumulation of an inter mediate (ornithine); (2) increased activity of ornithine δ-transaminase; and (3) a third, as yet, unclear process possibly involving feed-back regulation of arginine synthesis or the regulation of arginine breakdown to ornithine.

Lines of mice have been selected for up to 50 generations on the following traits: high body weight, low body weight, high fat content or low fat content. The lines selected for high or low body weight differ by a factor of 2·5 and those selected for high or low fat content differ by a factor of five, both traits measured in 10 week old males. A set of behavioural traits was measured to ascertain whether this selection had caused correlated responses in behaviour: studies included feeding behaviour, open field behaviour, ultrasound calling rates of pups, and the response to the introduction of a novel physical object. Alterations in behavioural patterns which were expected a priori were observed but there appeared to be no changes in behaviour associated with any one selection criterion. Estimates of the genetic correlations between selected and behavioural traits were, with one exception, generally less than 0·1 in magnitude and not significantly different from zero (the exception was food intake in lines selected on body weight). Assuming that mice are accurate models for commercial species, then these results have important implications for animal welfare: they demonstrate that large scale behavioural changes do not arise as an inevitable consequence of intense long-term selection on traits of economic importance in commercial species

Klebsiella aerogenes V9A carrying a lac plasmid in addition to its chromosomal operon showed strongly positive fermentation of lactose on MacConkey lactose agar plates, and was found to transport the lactose analogue thiomethyl-β-galactoside (TMG) at a rapid rate. The strain that had been freed of the plasmid showed moderate transport due to the chromosomal lac operon. When a plasmid bearing a mutation in lac Y was inserted into a strain with a normal Y gene, the resulting diploid became lactose-negative in phenotype. The presence of E. coli F′lac factors that carried lac Y mutations, whether deletions or missense or nonsense mutations, also rendered lac Y+Klebsiella lactose-negative. Such diploids, after growth in 1% lactose, transported TMG at a much lower rate than the corresponding plasmid-free lac Y+Klebsiella. However, this interference by lac Y− plasmids with the expression of the chromosomal lac Y gene was not seen when cells were induced with IPTG or when the chromosomal and plasmid lac operons were both constitutive. It was found that this effect of the plasmids was dependent on their possessing an intact lacZ gene.

The degree of heterozygosity as determined by electrophoretic analysis of three or four polymorphic loci correlates positively with survival in age groups of the American oyster (Crassostrea virginica) collected as spat from two different natural populations. The phenomenon is shown to operate in ages from 2 weeks (post-settlement) to 3 years and appears to be general in populations of marine molluscs. The most likely explanation for this result is that heterozygosity improves survival through its effect on growth (heterozygotes grow faster). The effects of individual loci on viability are independent of each other. A direct involvement of the enzyme polymorphisms is the most probable genetic interpretation of the data, but associative overdominance cannot be excluded.

A form of the human skin disease, ichthyosis, results from a mutation at the steroid sulphatase locus (STS) on the X chromosome. This locus appears to escape inactivation in the XX female, resulting in the expression of two doses of the STS gene (Shapiro et al. 1978; Crawfurd, 1982). The scurfy mutation in the mouse is thought to be homologous to the human disease (McKusick, 1978), and so should also be due to a steroid sulphatase (STS) deficiency. Our findings in male and female mice suggest that, in contrast to the human, the murine ‘STS’ locus is subject to X chromosome inactivation. However, another interpretation of the results is possible, namely that STS may be coded for by an autosomal gene.

In samples of sixteen populations of Rattus rattus from southern India, the oldest individuals have less variable molar widths than the younger ones. This is probably due to stabilizing selection by mortality. There is no detectable heterogeneity between sexes or teeth or among populations in this selection. Although there is no average difference between age classes in mean tooth width, the difference between age classes is heterogeneous among populations. This heterogeneity may reflect heterogeneity in directional selection or in direct environmental effects. The selection intensity on the variance is about 0·04.

Fifteen autosomal dominant mutations that cause cataract of lenses in mice were tested for allelism. The outcrosses of double mutants revealed three allelism groups, consisting of 5, 4 and 2 mutations as well as 4 mutations which segregated independently. The results indicated 7 different cataract loci in the sample of 15 mutations. The biomicroscopic examination of the eyes showed that phenotypically similar as well as very distinct cataract mutations can be alleles of the same gene. Conversely, phenotypically similar mutations were shown to be non-allelic.

A mutation resulting in increased triosephosphate isomerase (TPI) activity in blood was recovered in offspring of procarbazine hydrochloride-treated male mice. Breeding experiments indicated a codominant mode of expression. Compared to the wild type, heterozygous and homozygous mutants have mean erythrocyte TPI activities of approximately 140 and 190%, respectively. Besides blood and erythrocytes the increased activity is expressed to a similar degree in spleen, and to a lesser degree in liver, lung, kidney, muscle and brain. Enhanced activity was absent in the heart. Heterozygous and homozygous mutants are viable, fully fertile and exhibit no significant differences in haematological or other physiological traits studied. Biochemical investigations of TPI in both mutant genotypes revealed neither physicochemical nor kinetic differences compared to the wild type. Moreover, immunoinactivation studies showed no difference in the amount of antiplasma required to inactivate a constant amount of TPI activity in all three genotypes, strongly suggesting that the differences in enzyme activity are attributable to differing amounts of enzyme protein expressed per cell. Mapping studies indicated that the mutation is closely linked to the Gapd locus and consequently is located either adjacent to or within the Tpi-1 structural locus. It is hypothesized that the mutation affected a regulatory element contiguous to the Tpi-1 structural locus which acts by increasing the amount of TPI expressed.

An experiment was conducted with the flour beetle, Tribolium castaneum to investigate genotype-environment interaction. Ninety-two matings of one male and three females were made at random from a large panmictic population. The females were transferred to individual containers after 4 days. Six daughters were randomly selected from each sire–dam pair and individually mated to unrelated males. Three of the six were placed in an incubator (33·3°C., 45% relative humidity) and three in a cabinet at room conditions (22·2–26·7°C., 30–35% relative humidity) and allowed to produce eggs during a 3-day period. Progeny were counted as pupae and larvae. The traits studied were number of pupae and number of pupae plus number of larvae. A transformation to (X +1)½ was required. A conventional least-squares model was employed, and a large environmental effect was observed. In the incubator the mean number of pupae was 13·4 and of pupae + larvae was 20·1 while the corresponding figures for room conditions were 3·3 and 9·2. Genotype-environment interaction accounted for 3·7 to 6·7% of the total variance for (pupae + 1)½ and 2·1 to 8·3% for (pupae + larvae+ 1)½. Heritability of the traits was essentially the same in both environments. The interaction was due to an increasing difference between environments in production associated with increasing breeding values of the sire, and to small changes in rank of breeding values on the two environments. As a result of the interaction, selection in one environment for production on the other would be expected to be only 71 to 72% as effective as direct selection for (pupae + 1)½ and 62 to 86% for (pupae + larvae + 1)½ even though the fraction of the total variance attributed to genotype-environmental interaction was less than 10%.

The number and organization of amylase genes in Drosophila ananassae were investigated through classical genetic methods and in situ and filter hybridizations. At least four genes may be active in D. ananassae, organized as two independent pairs of closely linked copies on the 2L and 3L chromosomal arms. Several other species of the D. ananassae subgroup were studied and show the same chromosomal locations, suggesting an ancient duplication event. However, the number of Amy copies seems to be higher in the D. ananassae multigene family, and there is a striking intraspecific molecular differentiation.