Male mice from congenic lines carry Y-chromosomes derived from two pairs of inbred strains (CBA/FaCamSt and C57BL/FaSt; PHL/St and PHL-YH/St) on various genetic backgrounds were compared. Serum testosterone levels, and the response of target organs in castrated animals to graded doses of exogenous testerone propionate were measured. These comparisons produced evidence for two Y-chromosomal loci influencing androgen metabolism. One of these affects serum testosterone levels, with variant alleles on the Y-chromosomes derived from the PHL and PHL-YH strains. The other locus influences the response to testosterone of target organs, most significantly seminal vesicle, and variant alleles are found in the CBA and C57 strains. The effects of both loci are modulated by the genetic background. The relationship of these loci to other Y-chromosomal loci in the mouse is briefly discussed.

Diploid strains of Coprinus lagopus have been synthesized from common A heterokaryons either as oidial colonies or sectors. The criteria of growth rate and colony morphology on selective medium were used to distinguish between diploid and heterokaryon colonies. The average oidial size and hyphal width of diploid strains was significantly greater than that of the haploid parental strains.

Diploid monokaryons were very stable and only rarely produced haploid segregants. However, aneuploid intermediates in haploidization have been identified and these segregated further to give haploid monokaryons with recombinant genomes.

Dikaryons formed from diploid and haploid strains produced fruiting bodies. Meiosis and basidiospore production were irregular owing to the formation of triploid or partially triploid fusion nuclei in the basidia. In contrast to their stability in monokaryons, diploid nuclei tended to be unstable when combined in a dikaryon with a haploid nucleus, and often underwent partial haploidization before fruiting. Segregation of genes in the basidiospore progeny reflected whether haploidization had occurred before or after the formation of the fruiting body. If the haploid nucleus had a B mating-type allele common to the diploid nucleus, haploidization effected loss of the common allele.

Seven different genes, me-1 to me-7, controlling the steps in the synthesis of methionine in the Basidiomycete Coprinus lagopus have been tested for the production of prototrophs on minimal medium. Cultures carrying me-1 and me-7 produced prototrophs spontaneously at a rate of 2·6 × 10−5. These prototrophs were the result of mutations of suppressor genes and not due to back-mutation of the me-gene.

An intensive study of sixty-four mutants of an independent origin suppressing me-1 has revealed five different suppressor loci.

Tests for complementation between suppressor mutants and for their recessiveness to the wild allele were made in dikaryons.

All suppressor mutants were recessive to the wild allele. The five suppressor loci were all separated from one another by recombination, twenty-eight map units being the smallest distance between any two pairs. Mutants of the same locus did not complement one another, with few exceptions. Mutants of different loci, as tested in the trans-position in a dikaryon, complemented one another with the exception of pairs between sup-3, sup-4, and sup-5. Sup-3 and sup-4 are 28 units apart and are independent of sup-5 and yet they did not complement. This unique example of long-distance non-complementation is discussed in terms of gene action.

Two mouse-adapted scrapie agents of different sheep origin were compared. The titre, reached in the brains of mice in the terminal stage of scrapie, is of the same order for both agents. There is a threefold difference between the incubation periods of the two agents in some mouse strains, of which C57 is one, and in this strain incubation of the 22A agent, given as a large dose by a peripheral route, occupies almost the whole life-span.

The most fundamental difference between the agents concerns the reversal of the ranking of incubation periods, typically in the VM and C57 mouse strams: incubation of ME7 in VM takes almost twice as long as in C57, whereas most sub-lines of 22A take half as long in VM as in C57. The implications of this type of host-genotype, agent-strain interaction are discussed in terms of the possible nature of agent differences, the possibility of latent infection and the consequences for scrapie eradication programmes.

Our previous research (Raicu & Bratosin, 1966; Raicu, Hamar, Bratosin & Borsan, 1967) has shown that the Romanian hamster (Mesocricetus newtoni, 2n 38) is a well-established species, differing considerably from the Syrian hamster and from other hamster species. The species is spreading in the south of Romama, especially in Dobrudja, and in Bulgaria. Its spreading area is completely isolated from the spreading area of all other species of Mesocricetus. The preferred biotops are uncultivated fields, dry steppes and fields cultivated with fodder plants. The Romanian hamster reveals important differences in the number and structure of the autosomes and in the degree of homology and presence of chiasmata in the heterosomes.

The yellow mutant (y − 1:0·0) of Drosophila melanogaster shows a reduction in body pigmentation associated with a decrement in locomotor activity and in male competitive mating ability. The effects of the mutant gene are specific to locomotor activity in the adult fly, measures of larval activity being unaffected. In the presence of active females yellow males offer a reduced intensity of sexual stimulation because they are less able to maintain contact during courtship. However, the impaired locomotor performance of yellow males is not the general cause for their reduced competitive mating ability, since the stimuli provided by yellow mutants courting inactive females appear to be both quantitatively and qualitatively indistinguishable from those of their wild-type male sibs. Nor is there any good evidence, as measured by the frequency of rejection responses, that the courtship stimulation offered by the yellow males is less acceptable to the females. The mutant males are nevertheless unsuccessful in achieving copulation with such females. It is suggested that impairment of mating ability in yellow males may be caused by changes in the efficiency for mating of their secondary sexual structures due to the effect of the yellow gene on the properties of the cuticle.

Estimation of meiosis and sporuiation efficiencies in the fission yeast by ascus analysis

Genet. Res. (1979), 33, 109–119

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‘pi’ should read ‘Pi’

Morphology and the rate of RNA synthesis of the X-chromosome in XX/XO mosaic larval salivary glands of Drosophila melanogaster have been examined. For this purpose the unstable ring-X was utilized to produce XX and XO nuclei in the same pair of glands. The width of the X-chromosome and the left arm of the 3rd chromosome (3L) of larval salivary glands was measured and the rate of RNA synthesis by them was studied upon the use of [3H]uridine autoradiography in such XX (female) and XO (male) nuclei developing in a female background (i.e. otherwise genotypically XX). In such mosaic glands the width of the single X-chromosome of male nuclei is nearly as great as that of the paired two X's of female nuclei, as is also the case in normal male (X Y) and female (XX). The single X of male nuclei synthesizes RNA at a rate equal to that of the paired two X's of female nuclei and nearly twice that of an unpaired X of XX nuclei. Neither the developmental physiology of the sex nor the proportion of XO nuclei in a pair of mosaic salivary glands of an XX larva has any influence on these two characteristics of the male X-chromosome.

It is suggested that dosage compensation in Drosophila is achieved chiefly, if not fully, by a hyperactivity of the male X, in contrast to the single X inactivation in female mammals, that this hyperactivity of the male X is expressed visibly in the morphology and metabolic activity of the X-chromosome in the larval salivary glands of the male, and that this hyperactivity and therefore dosage compensation in Drosophila in general is not dependent on sex-differentiation, but is a function of the doses of the X-chromosome itself.

Relationships between protein genetic distance (D) and protein heterozygosity (H) were studied using allele frequency data for 42 proteins derived from multilocus electrophoretic surveys of genetic variation in over 200 invertebrate and over 300 vertebrate species. D¯ and H¯ values for the different proteins (mostly enzymes) were calculated, and large and significant correlations between D¯ and H¯ were found in comparisons of both intraspecific and interspecific populations. Empirical relationships between D¯ and H¯ were compared with neutral expectations under the stepwise model of neutral mutation with the assumption that populations are in equilibrium with respect to the effects of mutation and genetic drift.

At low divergence levels, a linear relationship of D¯ on H¯ was observed, but at high levels of divergence D tended towards an asymptote at high H¯. The results at high divergence cannot be explained using the approximate relationship D = 2ut (where u = mutation rate, t = time). However, computer simulations of neutral models showed that changes of this nature in the relationship between D¯ and H¯ were to be expected as divergence increases, the equation D = 2ut being a poor approximation at high D We therefore conclude that the observed relationships between D¯ and H¯ are, in fact, compatible with equilibrium neutral theory.

We have investigated the distribution of resistance genes in relation to genetic structure and gene flow between various islands of French Polynesia in Culex pipiens quinquefasciatus. We show that (1) resistance to organophosphorous insecticides, mediated by A2–B2 esterases, is present in all islands, (2) A2–B2 frequency decreases as distance from Tahiti increases, and (3) genetic differentiation (measured as estimates of the Fst, parameter from allozyme polymorphism) between islands is significantly correlated to geographic distances which is also correlated to air or sea commercial traffic. These data are discussed in relation to A2–B2 invasion of French Polynesian islands.