Curtailed (Tc) is a new T-allele which leads to complete or near-complete absence of the tail in heterozygotes, apart from a small caudal filament. Other heterozygous defects include absence of the axis odontoid process and of the nuclei pulposi, a tendency to have rib and vertebral fusions and a slight decrease in the average number of presacral vertebrae. Tc is lethal when homozygous, causing similar but more extreme defects than T, with absence of all limb-buds and non-closure of the neural folds. A comparison of Tc with other mutants suggests that the anomalies are mainly the result of more severe effects on the notochord-mesoderm system than in T. Differences between the genetic behaviour of T, Tc and Th are discussed.

Mice selected for large size show increases in both food intake and efficiency, and small mice show decreases in both. This is true whether the comparisons are made at the same age or at the same weight. Food intake and efficiency contributed more or less equally to the responses to selection for growth. Mice seem to regulate their food intake to a certain level of energy. On suspension of a period of food restriction, mice ate the same amount as others of the same strain that had not been restricted, and which were bigger. At the same time, they converted it more efficiently than the mice which had been full-fed throughout, because of a linear negative association between efficiency and body weight. Thus, following restriction, mice eat as much as bigger mice of the same age, and convert it as efficiently as younger mice of the same weight. The product of these two effects gives rise to rapid (compensatory) growth.

The variation shown by the Australian Commercial population of P. tuberosa in respect of date of ear emergence, seed weight and seedling weight has been analysed, and the interrelationships among the variables characterized. All three characters show appreciable additive genetic variation, in the sense that approximately seven generations of artificial selection would be sufficient to push the population mean for each trait beyond the range shown by introduced ecotypes.

Apart from the positive association between seed weight and seedling weight due to maternal influence, the three variables are to a large extent genetically independent in this locally adapted interbreeding population. It is therefore probable that the negative ecotypic correlations between seedling growth rate and date of ear emergence, and between seed weight and date of ear emergence, would rapidly be dispelled under random mating in a synthetic population.

Under open-pollination, date of ear emergence has been shown to be subject to phenotypic assortative mating of degree ρ = 0·78, approximately 53% of the variation being additive genetic. Variation in seed weight within the strain is extensive, with a heritability of 0·79. Neither character shows evidence of important genotype × years interaction.

Variation in seedling weight involves an appreciable genotype × environment interaction component, and has a heritability of only 0·17 which includes variation due to genetically determined maternal effects. The correlation between the seed weight of an ovule parent and the ‘ true’ mean seedling weight of the derived maternal half-sib group is of the order of 0·57. It has been estimated that the correlated response per generation in seedling weight, due to selection for seed weight, is 0·54 times that expected from direct selection.

Genet. Res., Camb. (1986), 47, pp. 93–102

Phosphatase regulation in Aspergillus nidulans: responses to nutritional starvation

By Mark X. Caddick, Alan G. Brownlee and Herbert N. Arst

An error occurred in the heading of Table 3 on page 98. The Table should read as follows:

Using seven newly induced duplications, three Minute loci have been located cytologically: M(3)hS 37 in 65F10–11; 66A (a new Minute locus), M(3)i in 67C, and M(3)hy in 68F; 69F. M(3)hS 37 and M(3)hy were previously thought to be allelic because they do not complement for lethality. The finding of Minute mutations with additive or synergistic rather than epistatic interactions makes us suspect that some other Minute mutations have been erroneously called allelic. The involvement of Minute loci in more than one biochemical pathway is discussed in view of the existence of synergistic interactions and of Minute loci without known mutant alleles.

Metaphase trivalent frequencies from a number of new chromosomal constitutions (various combinations of maize chromosome 2-Tripsacum homeologue primary and secondary interchanges) are presented and compared to previous findings from similar material. It is suggested than an underlying direct relationship may exist between extent of gentic map present in duplicate and triplicate and expectation from a sharing of map probability of crossing-over among all homologues. Theoretical considerations are discussed.

An aberrant chromosome 1 with two large homogeneously staining insertions was isolated from wild populations of Mus musculus musculus. The specific features of the aberrant chromosome have been described elsewhere (Agulnik et al. 1990). These include its preferential entry into the oocyte of heterozygous females, increased mortality of homozygotes and decreased fertility of homozygous females. Here we present data indicating that chromatid segregation in heterozygous females depends upon which sperm enters the oocyte before the second meiotic division: meioticdrive is powerful when it is sperm bearing normal chromosome 1, and segregation normalizesduring Mil when it is sperm bearing chromosome 1 with the extra segment. Experimental data are adduced and explanations offered for the observed phenomenon.

Drosophila melanogaster adults were collected throughout the summers of 1976 and 1977 in Hartford, Connecticut. The frequencies of the Adh isoalleles were determined and seasonal variation demonstrated. Correlation coefficients were calculated between Adh frequencies and the seasonal variations in temperature, precipitation, relative humidity and barometric pressure. Although five correlations were significant it was concluded that these were due to chance.

Genetic divergences between the wild mouse populations with various Robertsonian translocations from the Poschiavo Valley, Yugoslavia, Milan and the Apenninies, were estimated based on the mitochondrial (mt) DNAs. The mtDNAs isolated from the liver were analysed by agarose slab-gel electrophoresis after digestion with eight kinds of restriction endonucleases: BamHI, EcoRI, HindII, HindIII, PstI, HpaI, HpaII and BgII. These preparations were further used to make restriction maps, from which sequence divergence between each Rb variation was calculated to be 0·2–2·2%. These rather larger values appear to be in conflict with the present concept that the Rb variations occurred during the last several thousand years. Both, however, might be reconciled by assuming genetic introgression of the founder with a small number of Rb translocations into other subspecies populations genetically remote and the subsequent rapid accumulation of Rb translocations unique to each population due to an unknown mechanism occurring specifically in the intersubspecies hybrids between M. m. domesticus and the other M. m. subspecies. This was the case also in a new Rb (9.15) translocation obtained from Ogasawara Islands in Japan which was the intersubspecies hybrid between M. m. molossinus and M. m. domesticus.

1. Chromosomal polymorphism in two populations of D. subobscura from Barcelona has been analysed and compared with the polymorphism which has been reported from other populations.

2. In spite of microclimatic differences between the Barcelona sites, there is no evidence of differences in the frequency of inversion types nor of seasonal differences within one of these sites.

3. Regularities in the array of frequencies of chromosomal types in Barcelona and other populations suggest that the polymorphism is mainly adaptive although there is also evidence of differences due to distance which are not obviously associated with differences in habitat.

4. In general the index of free recombination gives higher values in the marginal populations of D. subobscura, but further data are needed to arrive at a definite conclusion on this point since the present evidence is rather ambiguous.

Mouse mutant genes which result in defects similar to those of medical importance in man may be of value as models for the study of the defect concerned. We report here a new gene causing congenital cataract in the mouse, which may be useful in the understanding of cataract in man.

A further point of interest is that Kratochvilova & Ehling (1979) have recently developed a new method of measuring increased mutation rates in the mouse, by examining offspring of animals treated with mutagens for the presence of cataracts due to mutant genes. For the purposes of this test it is valuable to have information on the number and map position of loci which can mutate to give cataracts.

1. TEM resembles X-rays in inducing dominant lethal mutations in the sperm of rats and mice and sterilizing type B spermatogonia. Beyond this, however, there are several important differences.

2. The relative ease with which TEM and X-rays affect sperm and spermatogonia varies greatly. The X-ray dose which produces 50% dominant lethals in sperm (500 rad) sterilizes spermatocytes and type B spermatogonia, and has such a drastic effect on type A spermatogonia that recovery of fertility is delayed for 2½ months. The TEM dose which produces the same mutation rate in sperm (0·1 mg./kg. rat) has no detectable effect on pre-meiotic stages. Even 1 mg./kg. only sterilizes the most sensitive stage, type B spermatogonia.

3. Taking immature sperm as the standard, mature sperm are more sensitive to X-rays, but less sensitive to TEM, and early spermatids, the most sensitive stage to X-ray-induced dominant lethals, are highly resistant to TEM.

4. Spermatocytes, in which X-rays yield a mutation rate equal to immaturesperm, are highly resistant to TEM.

5. To produce the same mutation rate in immature sperm, mice require twice as much TEM as the rat in mg./kg., though approximately the same X-ray dose.

6. In contrast to mid-stage rat spermatids, which are the most sensitive stage to TEM, mouse mid-stage spermatids are resistant.

An expression is derived for determining the probability of survival of a new favourable mutation in a large random-mating population with overlapping generations. For a gene of small effect, in a near-stationary population, an approximate formula similar to the usual one for discrete generations is obtained. The implications of these results for the evolution of life histories are discussed, using the partial derivatives of the chance of survival of a gene, with respect to changes in age-specific fecundities and survival probabilities. The properties of these derivatives are very similar to those of the derivatives of the intrinsic rate of increase, analysed by Hamilton (1966), thus providing a genetical basis for his conclusions concerning the evolution of life histories.

Comparison, by electrophoretic methods, of eel samples from Iceland, Scotland and Germany confirmed previous reports of uniformity in haemoglobin types. When liver esterases were examined, significant differences in the frequencies of phenotypes in the ‘fast’ zone of the electropherogram were found between samples from Germany and samples from Iceland and Scotland. The frequencies of transferrin phenotypes in Icelandic and Scottish eels differed significantly from those of French and American eels.

It follows that regional differences in gene frequencies probably exist within the species Anguilla anguilla. The implications for the ‘atlantic eel problem’ are briefly discussed.

A number of Hfr strains have been studied as to the action of radiations on the transmission of their genetic material to female cells. They form two classes, one in which irradiation produces only lesions that prevent transfer, and one in which new modes of chromosome transfer seem to be induced. One group of strains, derived from a common F+ male, appears to give rise to the same induced mode of transfer, while no correlation could be found in the other Hfr's studied.

The distribution of 13 transposable element families along 15 X chromosomes from an African natural population of Drosophila simulans was determined by in situ hybridization to polytene chromosomes. The transposable elements cloned from Drosophila melanogaster all hybridized with Drosophila simulans chromosomes. The number of copies per family was 3·5 times lower in the latter species and correlated with the copy number per family in Drosophila melanogaster. With the exception of 297, the copy number per chromosome followed a Poisson distribution. Element frequencies per chromosome band were generally low. However, several sites of the distal region and the base of the X chromosome had high frequencies of occupation. Elements had higher abundance at the base of the chromosome compared to distal regions. Overall, the distribution of transposable elements in Drosophila simulans is similar to that found in Drosophila melanogaster. These data provide evidence for the operation of a force (or forces) opposing transpositional increase in copy number, and that this force is weaker at the bases of chromosomes, consistent with the idea that recombination between elements at non-homologous sites contains TE copy number. The reduction in copy number of all TE families in Drosophila simulans compared to Drosophila melanogaster can be explained by stronger selection against transposable element multiplication and/or lower rates of transposition in Drosophila simulans.