Methods for the analysis of the joint transmission of two phenotypes are described and used to determine the extent to which lipoprotein concentrations share a common genetic and/or environmental background. Analysis of data on 160 Caucasian nuclear families revealed that the observed phenotypic association between high-density cholesterol (HDL) and low-density cholesterol (LDL) could be accounted for in terms of common family environmental effects alone (estimated genetic correlation, ρG = −0·132±0·136; estimated residual environmental correlation, ρR = 0·065±0·230). The association between HDL and very-low-density cholesterol (VLDL) could not be accounted for in terms of family environmental effects alone. For HDL and VLDL the residual environmental correlation was significant while the genetic correlation was not (ρG = −0·111±0·214, ρR = −0·421±0·172). The correlation between LDL and VLDL also could not be accounted for in terms of common family environmental effects alone, although here a genetic relationship appears to be the important factor (ρG = 0·330±0·192, ρR = 0·010±0·217).

This paper describes analytical and simulation models of the population dynamics of transposable elements in randomly mating populations. The models assume a finite number of chromosomal sites that are occupable by members of a given family of elements. Element frequencies can change as a result of replicative transposition, loss of elements from occupied sites, selection on copy number per individual, and genetic drift. It is shown that, in an infinite population, an equilibrium can be set up such that not all sites in all individuals are occupied, allowing variation between individuals in both copy number and identity of occupied sites, as has been observed for several element families in Drosophila melanogaster. Such an equilibrium requires either regulation of transposition rate in response to copy number per genome, a sufficiently strongly downwardly curved dependence of individual fitness on copy number, or both. The probability distributions of element frequencies, generated by the effects of finite population size, are derived on the assumption of independence between different loci, and compared with simulation results. Despite some discrepancies due to violation of the independence assumption, the general pattern seen in the simulations agrees quite well with theory.

Data from Drosophila population studies are compared with the theoretical models, and methods of estimating the relevant parameters are discussed.

Population genetics of extranuclear genomes is further developed under the neutral-mutation random-drift hypothesis, and the characteristic evolutionary aspects are summarized. Several formulae derived here are concerned with the variances of genetic variability (gene identity) at a single extranuclear locus and the evolutionary distance between two isolated populations which is estimated from a comparison of homologous linked nucleotide sites. Two types of variance are considered; one is the variance in the entire population (VQ) and the other is the variance within a single germ cell (VH). When compared with a Mendelian genetic system in a panmictic population, an extranuclear genetic system has the following equilibrium properties: (1) the mean genetic variability is low if, despite the high multiplicity of the genome in a cell, the proportion of the cytoplasmic contribution from the male's gamete is small, (2) the effect of recombination is small and a large amount of variance of linkage disequilibrium tends to be maintained, (3) the overall relationship between the mean and variance of genetic variability does not much differ but VQ (VH) is expected to be small if the paternal contribution is small, and (4) the evolutionary distance estimated depends on the extent of intrapopulational variation in a common ancestor population which in turn depends on within-cell variation. I argue that there is an analogy between the model of extranuclear genomes in a finite population and that of nuclear genes in a subdivided population. The analogy helps our understanding of some properties in an extranuclear genetic system.

A new mutant (Wct) has been identified at the W locus of the mouse. The homozygote is poorly viable. Whereas the heterozygote (Wct / +) is only mildly anaemic like Wυ / +, the double heterozygote Wct + / + Ph is considerably more anaemic than Wυ + / + Ph and it and Wsh + / + Ph have significantly raised leucocyte counts. Wct + / + Ph is also unduly radiosensitive to whole body X-irradiation, 50% dying from haematopoietic failure at a dose of 4·59 ± 0·14 Gy, whereas the median for Wct / + was 6·49 ± 0·28 Gy. Serial blood counts of mice after low- or sub-lethal doses of X-rays revealed significantly more profound depression of counts of both red cells and leucocytes in Wct +, and more notably in Wct + / + Ph, than in + / + or Wsh / + (haematologically normal) iso-dosed mice. We conclude that control of haematopoiesis by chromosome 5 is not confined to the W locus but is shared by the linked gene Ph (and perhaps Rw) and that expression of the change is not limited to the erythron but involves the pluripotent haematopoietic stem cell.

We studied the evolutionary dynamics of extranuclear genes taking into account simple kinds of selection, two modes of inheritance and the multiplicity of genomes within a cell. Particular attention was paid to the accumulation of advantageous or deleterious mutations in an extranuclear genome. Within-generation drift due to multiplicity of genome and non-Mendelian segregation promotes the fixation of advantageous mutations and prevents deleterious mutations from accumulating. We show also that the extent of paternal contribution makes little difference in the rate, but, in contrast, the configuration of the genome and the mode of transmission both makes a large difference. These results are compatible with what is known about extranuclear genomes.

Individual and within-full-sib family selection for low sternopleural bristle number was carried out for 17 generations, with six replicate lines for each selection method. Our results can be summarized as follows: (1) the response to selection was exhausted very quickly, (2) the additive variance of the selected lines declined rapidly, (3) the variation in response to selection decreased as selection progressed, (4) genetic differences among replicates at the selection limit were small, (5) individual selection resulted in a higher initial response than within-family selection, but similar limits were achieved with both procedures. These observations are consistent with the hypothesis that the pattern of response to selection is due to the segregation in the base population of only a few loci with large effects, at intermediate frequencies.

A complete genetic map has been established for the P22 clear plaque forming mutations cir4-l, cir5-l and cir6-l. These are located within or closely linked to the immI region of P22 and represent a new class of clear plaque forming mutants located outside and rather distant from the immC region. They were mapped with respect to the markers mnt, vy and ant of the immI region and to genes 16 and 9 which span it. The three cir mutations complement each other and – with one possible exception – the cl, c2 and c3 mutations of the immC region. P22 cir6-l – like P22 cir5-l (Harvey et al. 1981) – is suppressed by the ant−am19 allele, whereas P22 cir4-l is not. The results are discussed in terms of the regulation of early ant expression.

Amoebae and plasmodia are alternate vegetative forms in the life cycle of the acellular slime mould Physarum polycephalum. Haploid amoebae carrying heterothallic alleles of the matA (or mt) locus ordinarily form plasmodia only by crossing, but occasionally give rise to mutants that form plasmodia by selfing as well as by crossing. Twelve independently isolated mutants of this type have been studied. Eight carry mutations (termed gad or greater asexual differentiation mutations) within approximately 0·2 map units of matA. Another mutation (gad-12) is linked neither to matA nor to any of 9 other markers tested. The remaining three mutations are linked to matA and map as follows: matA–0·5 units – gad-4–4 units – gad-6 – 8 units – gad-11. One mutation, gad-11, has been tested in strains carrying each of the five matA alleles (matAl, 2, 3, 4, and h) available in a common genetic background; the mutation is expressed with all five alleles. The mutation npfF1 (formerly aptA1), which was isolated as a suppressor of selfing in Colonia (matAh) amoebae, suppresses the action of each of the 12 gad mutations. The similarly isolated mutation npfA1 is also epistatic to eight of the mutations, but permits selfing with gad-5, 6, 12 and 13. For double mutant strains containing gad-12 and gad-1, 2, 4, 6 or 11, the selfing behaviour of each double mutant differs from that of either single mutant. Mixtures of gad−npfF1 with gad+npf+ amoebae readily form plasmodia, a result suggesting that gad mutations are dominant or semi-dominant. We conclude that the commitment of a cell to differentiate into a plasmodium is under the control of a complex group of genes linked to matA.

Epididymal sperm from male mice carrying tw32 (t12 complementation group) exhibit a peculiar nonprogressive type of motility called ‘dancing’; sperm from congenie wild-type mice do not. To determine whether this effect was unique to tw32 or common to all t haplotypes, sperm from mice carrying other t haplotypes were examined. A male was considered to have nonprogressive sperm if more than 20% of the motile sperm had nonprogressive trajectories. The mean percentage of nonprogressive but motile sperm for 33 wild-type and Brachyury males of various genetic backgrounds was 4. All males carrying tw12 (tw1 complementation group), tw5 or tw73, and 56% of males carrying t0 or tLub1 had nonprogressive motile sperm. Five per cent of males carrying t chromatin or a deletion in the proximal (to the centromere) half of the t complex had nonprogressive motile sperm, but all males carrying t chromatin in the distal half of the t complex had nonprogressive motile sperm. These observations suggest that the factor or factors causing nonprogressive sperm motility may be common to all complete t haplotypes, and located in the distal region of the t complex.

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.

Haploid amoebae of Physarum polycephalum may form plasmodia sexually by ‘crossing’, which involves cellular and nuclear fusion, or asexually by ‘selfing’, which occurs without nuclear fusion. In most amoebal strains, selfing is seen in clonal cultures only at very low frequency. In the present study, we have shown that selfing occurs at a similarly low frequency in mixtures of crossing-incompatible amoebae, but is stimulated in crossing-compatible mixtures. In certain compatible mixtures involving mutant strains, where crossing is temperature-sensitive, selfing may be stimulated even at a temperature that largely or wholly abolishes crossing. The extent to which selfing is stimulated appears to be influenced by matB, a locus which is known to affect the frequency of amoebal fusion. We have failed to detect any filter-transmissible factor that might be responsible for the effects we have observed. We suggest a sequence of events that might bring about ‘stimulated selfing’ as a consequence of abortive crossing.

Genetic variation in the amount of binding of dihydroalprenolol (a potent antagonist) to hepatocyte β-adrenergic receptors has been observed among inbred strains of mice. This variation is attributed to a differential effect of magnesium on the receptors between the high and low binding strains. Evidence for a single gene controlling the magnesium effect on dihydroalprenolol binding to β-adrenergic receptors was found using recombinant inbred lines between the high and low strains. We suggest the provisional gene symbol Badm.

Two spontaneously arising chromosome rearrangements were isolated in Sordaria brevicollis from one perithecium. These were detected through increased production of black spores in intercrosses of complementing buff spore colour mutants. One was a reciprocal translocation between linkage groups I and II; the other a reciprocal translocation between linkage groups II and VI. In the former case the translocation resulted in frequent non-disjunction generating black spores which were either tertiary or interchange disomics. The frequency of premature centromere division was also increased. In the case of the translocation involving linkage groups II and VI the black spores were formed as a result of adjacent-1 segregation and were probably duplication/deficiency products.

In both rearrangements the breakpoint in linkage group II was, as far as could be judged, in an identical place. This and the fact that they were isolated from a single fruiting body, suggests that the chromosome breakage event arose as a potential lesion, which replicated before the potential break was either restituted, to restore a normal chromosome, or opened, to form the rearrangements.

We report the results of an ontogenetic analysis of quantitative genetic variance components with two replicates drawn from the randombred ICR strain of mice. A total of 432 mice from 108 full-sib families raised in a cross-fostering design were used to estimate direct effects heritability, maternal effects, and environmental effects for weight, head length, trunk length, trunk circumference, and tail length at 17, 24, 31, 38, 45, 52, 59, and 66 days of age. There was no significant difference in heritability between the replicates. Heritabilities either stayed more or less constant with age at about 0·30 (weight, trunk length, trunk circumference) or increased slightly with age (head length, tail length). Maternal effects decreased with age from a maximum of about 0·50 at weaning to about 0·15 at age 66 when growth was nearly complete. Environmental effects increased in relative importance during ontogeny.

A series of six bones from samples of mice from eleven inbred strains and one F1 hybrid were measured using a simple apparatus. The bones examined were the mandible, os coxae, femur, tibia–fibula, scapula and humerus. Considerable variation in the shape of each bone was found and successful discrimination between the strains was obtained. Correct strain classification ranged from 87% for the scapula to 98% for the os coxae. Gross abnormalities and quantitative variants were identified.

As the pattern of discrimination is different for each bone, the use of other bones in addition to the mandible may improve resolution in the identification and quality control of mouse stocks. The objective and precise identification of abnormal and variant bones suggests that the method may be useful for population studies and for the detection of induced skeletal abnormalities in toxicological investigations.

The expression of electrophoretic variant forms of the X-linked enzyme phosphoglycerate kinase (PGK-1) was examined during the ontogeny of the female germ-line following X-chromosome reactivation. Non-growing oocytes from foetal and neonatal ovaries of heterozygous females show a higher PGK-1A isozyme activity, a reflection of prior non-random X-inactivation favouring activity of the X-chromosome carrying the Pgk-1a allele and Xcec locus. On oocyte growth, the total PGK-1 enzyme activity increases 40–50 fold and the pattern of PGK-1 isozyme expression changes giving an electrophoretic pattern now skewed in favour of the PGK-1B isozymic form. Activity of the PGK-1B isozyme exceeds that of PGK-1A in all growing oocytes with a total activity greater than 0·075 nmol h−1 oocyte−1. Mice homozygous for either Pgk-1 allele show similar PGK-1 specific activities in somatic tissues where one X-chromosome is active, but oocytes of Pgk-lb homozygotes show a higher specific activity compared to those of Pgk-1a homozygotes. Thus increased activity of the PGK-1B isozyme relative to the PGK-1A isozyme is specific to growing oocytes.

Houseflies collected from eight pig-breeding farms were used to investigate the nature of sex determinants in fly populations of South-East England. Earlier observations had shown that their sex determination mechanism was not of the standard (XX females, XY males) type.

Most flies of both sexes were XX; the male determining Y chromosome of standard populations was rare. Test-crosses to females of standard multimarked strains and crosses using aneuploid (OX) flies identified two dominant male determinants, one on autosome 3 (M III) and another on the X chromosome (Xm), and provided the first demonstration in this species of an active involvement of the X chromosome in sex determination. A small secondary constriction on X appeared to indicate reliably the presence of Xm. Most individuals in field populations were Xm homozygotes, implying the presence of an unlocated female determinant F,† epistatic to Xm and M III.

M III was less common and differed in frequency between samples. Its increased frequency in a strain selected in the laboratory with the pyrethroid insecticide permethrin might be due either to genetic drift, or to linkage between M III and a gene on autosome 3 that confers resistance to pyrethroids in houseflies.

The steel allele, contrasted (Slcon), arose in a neutron irradiation experiment. Slcon is fully penetrant and heterozygotes can be recognized at or soon after birth by darkly pigmented external genitalia in both sexes, while the adult coat tends to be a little lighter than normal. Homozygotes also have dark genitalia and a markedly diluted coat. Both eumelanin and phaeomelanin are affected, with reduced numbers of cortical and medullary pigment granules in the hairs. Contrasted also affects the haematopoietic system, causing slight macrocytic anaemia in the homozygote. Slcon homozygous males are fertile but testes weigh on average 20% less than in their heterozygous litter-mates. Homozygous females are usually sterile although if mated early (4½−6 weeks) they occasionally have a single litter. Ovarian sections showed a gradual degeneration of oocytes in Graafian follicles so that most had gone by 2 months. Similarly, vaginal smears indicated that after about three normal cycles homozygous females lapsed into a state of persistent dioestrus; injections with gonadotrophins did not prolong their period of fertility or cause a resumption of their oestrous cycles. The effects on fertility, pigmentation and haematology of contrasted when combined with other steel alleles are also described.

To determine the extent of gametic disequilibrium between loci linked to the t-complex in house mice, alleles of four allozyme-encoding loci associated with eleven t-complexes recently found in wild mice and sixteen t-complexes maintained in laboratory colonies were identified. The allozyme-encoding loci included in the survey were complement component-3, kidney catalase, glyoxalase-1 and phosphoglycerate kinase-B. In contrast to published surveys showing strong disequilibrium between the H-2 complex, t-complex protein-1 and the t-complex, disequilibrium between the t-complex and linked allozyme-encoding loci was not detected. This result is discussed in terms of several hypotheses concerning the structure of mouse populations and the mechanisms maintaining gametic disequilibrium between the H-2 complex, t-complex protein-1 and the t-complex.

Heterokaryons of N. crassa were synthesized from homokaryotic strains differing in sterol composition and sensitivity to the polyene antibiotic nystatin. Mycelia of the nystatin-sensitive strain erg-1+ contained ergosterol and episterol, and the nystatin-resistant mutant erg-1 contained fecosterol and lichesterol. Mycelia of heterokaryons with different proportions of erg-1+: erg-1 nuclei contained various proportions of the four sterols. Ergosterol was the principal sterol in heterokaryons with more than 5% erg-1+ nuclei.

Heterokaryons with various proportions of erg-1+:erg-1 nuclei were grown for several weeks along tubes of synthetic media. Growth rates were stable on minimal medium and nutritionally supplemented media but nuclear proportions often fluctuated. Growth rates fell sharply on nystatin-supplemented media and there were adaptive increases in proportions of mutant erg-1 nuclei which resulted in selection of nystatin-resistant homokaryotic mycelia.