Relationships between mating type genes and mating-inducing factors (gamones) were investigated in the ciliate Euplotes patella syngen 2. Ten mating types were distinguished, and genetic data indicated that the ten mating types were determined by four codominant alleles in possible combinations of two of them. There were six heterozygous types (mt1/mt2, mt3/mt4, etc.) and four homozygous types (mt1/mt1, mt2/mt2, etc.). Conjugation-conditioned fluid (CCF) obtained from a mixture of cells of homozygous types could induce homotypic pair formation in cells of all mating types except for a particular type. Genetic data of cell-CCF combination experiments suggest that each mating type allele controls the production of a specific gamone which induces pair formation in cells which do not produce the same gamone. Gamones and their hypothetical receptors are discussed.

A new CNR (caudatum non-reversal) mutant of Paramecium caudatum was isolated after gamma ray mutagenesis. This CNR lacks not only the transient inward Ca2+ current but also the sustained Ca2+ current. It was shown to complement the three known CNR mutants of P. caudatum (cnrA, cnrB and cnrC) by crossbreeding analyses. Thus, this new mutant belongs to a 4th CNR locus, designated cnrD. The defect of cnrD can be partially rescued by microinjection of cytoplasm from any of the three CNR mutants or the three Pawns (pwA, pwB and pwC) in P. tetraurelia. Since the three CNR genes have been shown to be different from the three Pawn genes by cytoplasmic complementation test (Haga et al. 1983), this result suggests that cnrD is the 7th non-excitable mutant in Paramecium. Thus, there are at least seven genes controlling Ca2+ channel function in Paramecium.

Salmonella typhimurium strains of biotype 25x have been shown in transductional cross experiments to be clonal in the Nad character. The ancestral bacterium, probably of biotype 25a, mutated to a requirement for nicotinamide and subsequently diversified in phage type and secondary biotype characters. Such a sequence of events indicates interconversion among phage types 6, 16, 46, 49, 73, 76 and 135. Strains in biotypes 1x, 9ix, 17x, 17dx, 19dx and 25hix yielded Nad+ recombinants in interbiotype crosses, suggesting that each originated as an independent mutant line.

A natural population of the tetrapolar fungus Coriolus versicolor (L. ex Fr.) Quel, in a small woodland was observed over 3 years. Dikaryotic members of the population were identified using intraspecific antagonism and mating type markers. Records were kept of the distribution, longevity and fruiting behaviour of 44 individuals. Zone lines between individuals were found to remain constant in position throughout the study, but rates of decay and fruiting times varied between dikaryons and did not seem related to resource size. Detailed maps of the genetic structure of the populations in two stumps are presented. In general the results indicated thousands of alleles at both mating type loci. Repeated occurrences of alleles were very rare, when the data were interpreted rigorously in terms of the probable origins of the nuclei found in individuals. This approach was also applied critically to some published data. Comparisons were made between alleles found in local and more widely gathered samples, and led to estimation of worldwide frequencies but it is concluded that such exercises are of limited value.

Genes controlling the synthesis of the D group of low-molecular-weight (LMW) subunits of glutenin occur on the short arms of chromosomes 1B and 1 D. Their position on chromosome 1 B, relative to the storage protein loci Glu-B1 (long arm) and Gli-B1 (short arm), was estimated by analysing the backcross-one progeny of two different crosses. To estimate recombination between the D subunit genes and Gli-B1, half grains were analysed by two-dimensional electrophoresis. The Gli-B1 locus contains genes for the B group of LMW glutenin subunits, γ-gliadins and ω-gliadins although only the latter were made use of in this study to distinguish the parental alleles. Additionally, the complementary half grains were analysed by sodium dodecyl sulphate, polyacrylamide-gel electrophoresis to estimate recombination between Gli-B1 and Glu B1, coding for high-molecular-weight (HMW) glutenin subunits. The D subunit genes occur at a new locus, provisionally defined as Glu-B2, which lies in between Glu-B1 and Gli-B1, 17 cM from the former and 22 cM from the latter. On the basis of previous mapping data involving Gli-B1, it was concluded that the D subunit genes occur close to the nucleolar organizing region and probably on the short-arm satellite, like Gli-B1.

Two laboratory strains of the green alga Chlamydomonas reinhardtii137c differ in their pattern of phototactic aggregation. One is positively phototactic under conditions where the other is negatively phototactic. The trait segregates 2:2 in tetrads and maps to a single locus. Heterozygous diploids are positively phototactic, showing that this allele is dominant. The aggregation pattern caused by either allele is not altered by the introduction of an unlinked gene that suppresses development of the eyespot. Probably the strains already differed in phototactic behaviour at the time they were first isolated. They may therefore reflect a genetic polymorphism common among soil algae. The genetic data allowed another significant observation not specifically related to phototaxis. Anomalous products from some crosses suggest that four nuclei sometimes fuse into a tetraploid zygote that then undergoes meiosis. The meiotic products that result are diploid. This represents a previously undescribed mechanism of diploid formation in Chlamydomonas.

The genetic basis of slow growth rate and aberrations in the ciliary pattern was studied in the multi-left-marginal variant of Paraurostyla weissei. The 3:1 segregation in F2 sibling crosses and 1:1 segregation in test crosses indicate that the aberrant phenotype is controlled by a recessive allele at a single gene locus termed mlm. The phenotypic change from wild type to mlm takes place about 5–8 cell cycles after conjugation. The study established that total conjugation in P. weissei is a true sexual process in which meiosis, fertilization and Mendelian segregation occur.

Transcription in 9A–11A aneuploid mosaic female larvae of Drosophila melanogaster has been assessed autoradiographically. Eleven larvae were found to exhibit mosaicism out of sixty-six larvae scanned and the percentage of XO and XX nuclei varied from approximately 9 to 100. Irrespective of the number of XX nuclei present the XO nuclei (duplicated for 9A–11A) invariably showed hyperactivity for both the segments. The XX nucleus exhibited a dosage effect for all the three segments of 9A–11A. Results support the transcriptional constancy of the entire X chromosome, as proposed by Maroni and Lucchesi. Cellular autonomy of hyperactivity of the single X chromosome even at the level of segments of the X is thus evident from the present results.

Variability in fertility in compound chromosome (CC) strains of Lucilia cuprina (Wiedemann) is directly correlated with the segregation properties of the CCs in those strains. In compound fifth-chromosomes, high fertility (up to 50% ) is associated with high frequencies of segregation of the left element (C(5L)) from the right element (C(5R)) in males, while low fertility (up to 25%) is associated with random assortment of the CCs in males. Regular segregation of C(5L) and C(5R) chromosomes in males is associated with particular C(5L) elements, which contain cytologically visible duplications of 5R chromatin. These duplications may contain a site which is normally involved in the pairing of the fifth chromosomes in males.

In females the CCs segregate from one another with a frequency of 89%. None of the C(5R) elements studied affected segregation in males, and neither C(5L) nor C(5R) elements had any demonstrable effect on segregation in females. Transmission of certain CC elements through one or both sexes is significantly lower than expected. This could have a variety of causes, such as meiotic drive, inviability associated with position effects, or homozygosis of deleterious mutations on homologous CC arms during meiotic crossing over in females. The CC strains released during a field trial of genetic control contained both high-fertility and low-fertility C(5L) chromosomes. Both types of CC were subsequently recovered from individuals which had overwintered in the field. Over a period of several generations following this recolonization one particular high-fertility C(5L) chromosome increased in frequency to near-fixation, despite the presence in this chromosome of deleterious mutations.

Crossover frequencies within three overlapping heterozygous paracentric inversions of differing length in the long arm of chromosome 1 of maize were estimated from cytological data. These frequencies were found to be close to normal for the regions involved and directly proportional to the respective physical lengths of these inversions. It is suggested that if pairs of centres which are specialized to regulate homologous pairing of the region between them exist in this part of the maize genome, they are most probably numerous and widely distributed.

Drosophila melanogaster, D. simulans and D. mauritiana are closely related species, the first two cosmopolitan and the last restricted to the oceanic island of Mauritius. D. simulans and D. mauritiana are the most closely related pair, with the latter species probably resulting from a founder event. The relatedness of the three species and their ability to hybridize allow tests of recent theories of speciation. Genetic analysis of two characters differing between D. simulans and D. mauritiana (sex comb tooth number and testis colour) show that the differences are due to at least five and three loci respectively. Behavioural tests further demonstrate that sex combs are probably used by males at a crucial step in mating, and that the differences between the two species may be related to differences in their mating ability. These genetic studies and previous work indicate that differences among these species are polygenic and not (as proposed by recent theories) attributable to only one or two loci of large effect. Further studies of interspecific hybrids show that genetic divergence leading to developmental anomalies is more advanced in the older species pair D. simulans/D. melanogaeter than in the younger pair D. simulans/D. mauritiana. This supports the neo-Darwinian contention that reproductive isolation is one step in a continuous process of genetic change among isolated populations, and does not support current theories that such change occurs only during the evolution of reproductive isolation. Finally, investigations of the degree of gonadal atrophy and its sensitivity to temperature in D. simulans/D. mauritiana hybrids fail to support recent speculations that phenomena similar to hybrid dysgenesis (which causes such atrophy in D. melanogaster) play a role in speciation.

By means of genetic mosaics we have studied the cell autonomy of mei-41 and mei-9, two loci involved in DNA metabolism. The frequency of spontaneous somatic spots resulting from unrepaired chromosome damage and the sensitivity of mutant cells to killing by X-irradiation - two traits indicative of deficient DNA repair - have been analysed at the cellular level. The results show that: (1) The effect of both mutations on chromosome stability is cell autonomous. (2) After 1000 r of X-irradiation practically all the cells homozygous for mei-41 disappear while about one-third of the cells homozygous for mei-9a survive the irradiation. The possibility of using these mutants as tools to approach developmental problems is discussed.

Aggregation chimaeras were constructed by fusing embryos homozygous for sash (Wsh) with fuzzy, leaden beige (fz, ln, bg) homozygotes to investigate the site of action of the beige and leaden loci. The genotype of the hair follicle was identified by fuzzy alleles (+ +fz or fzfz). All melanocytes were derived from the fuzzy leaden beige population, as sash homozygotes do not produce functional melanocytes. Reciprocal recombinant epidermal/ /dermal skin grafts were constructed from 14-day embryonic skin of homozygous fzln bg and either albino (aa cc) or pink-eyed dilution (pp) embryos to test for any dermal expression of leaden or beige, since the epidermal and dermal genotype of the chimaeric hair follicles could differ.

Patches of fuzzy and non-fuzzy hairs were distributed throughout the coats of two of the three chimaeras obtained. The pigmented regions were blue grey, typical of the leaden beige interactive phenotype. Large abnormal beige granules were found in fuzzy and non-fuzzy hairs. Melanocytes in both classes of growing follicles were nucleopetal, typical of leaden. Similarly, the results of the 14-day skin grafts showed that the beige and leaden loci are melanocyte-autonomous.

The chimaeras showed a pigment distribution resembling the heterozygous sash phenotype. Thus the 1:1 gene dosage of sash: wild type in heterozygotes and chimaeras has an overall effect on pigment pattern that overrides the predicted random distribution of the melanocyte precursors.

Examination of the eyes with a slit lamp revealed that 101/H mice had a coloured cataract. Crosses to C3H/HeH indicated that this was inherited as a single recessive gene which we have designated lop-2 (lens opacity-2). The related strain 129/Sv-SlJ-CP had a phenotypically identical cataract and presumably also carries the lop-2 gene. CBA/H, CBA/CaH- + /p, CBA/H-kd and CBA/H-T6 mice had a bright white or white/green cataract that typically extended from the nucleus to the anterior cortex of the lens. Crosses to C3H/HeH indicated that this was inherited as a semi-dominant gene. However, other crosses raise the possibility that the CBA cataract is also caused by lop-2. If so, the expressivity (and penetrance of the heterozygote) is affected by genetic background. Neither lop-2 nor the gene responsible for the CBA cataract was linked to contrasted (Slcon) on chromosome 10, so these are distinct from the Lop (lens opacity) gene. Further studies of genetic linkage are needed to clarify whether lop-2 is responsible for both the 101/H and CBA/H cataracts.

The male mating ability and male fertility of 40 third chromosome homozygote lines has been measured. There was significant between-line differentiation for both characters, and comparison with a heterozygous stock indicated inbreeding depression and hence dominance variation for them. The characters showed significant positive correlation both with each other and with other fitness components and total fitness, as measured by Mackay (1985). This pattern of large positive correlations between fitness components is not expected to occur in outbred populations.

A tricomplex heterozygote has a synthetic chromosome complement consisting of four pairs of arms of chromosomes 2 and 3 in the form of a compound of two homologous arms (a homocompound) and of three compounds of two nonhomologous arms (heterocompounds), each being homologous to an arm of different compounds. In meiosis, pairing of homologous arms results in the formation of a single and a multiple configuration that are structural equivalents of a univalent and a trivalent. Data are presented indicating that, in a given complement, the pattern of the distribution of three heterocompounds at division I is the same in males and in females. The distribution depends on the arrangement of the 2nd and the 3rd chromosome centromeres in the trivalent. In configurations presumed to be homocentric (all three chromosomes having homologous centromeres), the distribution was random or nearly random while, in configurations presumed to be heterocentric, the distribution appears non-random, with one of the segregation alternatives being roughly twice as frequent as either one of the two other alternatives that were more or less equal in frequency. The results could be explained in terms of the 3rd chromosome centromere being ‘strong’ in directing the two 2nd chromosome centromeres to the opposite pole at division I, an explanation implying a functional differentiation of the two autosomal centromeres or adjacent sequences. Data are also presented showing that in females the distribution of the homocompound is non-random with respect to the distribution of the heterocompounds; the homocompound was recovered preferentially together with the single one of the three heterocompounds. This is inconsistent with the prediction based on the theory assuming an existence of two independent pairing pools.

Unstable alleles, broken chromosomes and stable mutants have arisen in maize out of infected plants of Barley Striped Mosaic Virus and other viruses. Surprisingly, these same events have appeared out of progenies of these infected plants that themselves do not show any infection. These mutants showing instability have resulted from insertions that are not necessarily related. Two of these insertions (BS1 and TZ86) that have been analysed molecularly have the general characteristics of maize insertions with terminal inverted repeats and host duplication at the terminus of the transposon. In other experiments three of the unstable alleles at the a locus in maize (A locus, chromosome 3, short arm; one of genes for anthocyanin control) that arose in derivative lines of the initially treated plants are responsive to a transposable element, the Uq element. It was determined that the Uq element was not present in this initially treated plant but was present in the untreated female plant. It is proposed that the initial treatment induced events that in turn led to the mobilization of elements and that these events continue to occur in later generations. It seems that genomic events once initiated such as mobility of elements cannot be terminated despite a discontinuation of the treatment (virus) and, like a Frankenstein monster, is not responsive to its maker.

Weekly food intake and body weight were measured from 3 to 17 weeks of age on mice selected 14 generations for increased and decreased values of one of three criteria: appetite (A) as measured by 4- to 6-week food intake, adjusted by phenotypic regression to minimize change in 4-week body weight; fat percentage (F), using the ratio of gonadal fat pad weight to body weight at 10 weeks of age and total lean mass (protein, P), using the index body weight in 10-week males— (8 × gonadal fat pad weight). Carcass composition analyses were undertaken on the 17-week-old mice, and are presented along with composition data for younger mice from earlier generations. The high intake A line mice are larger, eat more, have higher maintenance requirements and are slightly leaner than the low intake A line mice, but are no more efficient. The increased lean mass P line mice are much larger, eat more and are more efficient than the decreased lean mass P line mice, but show little difference in maintenance or carcass composition. The (much) fatter F line mice are larger, more efficient and eat more during the rapid growth period than their leaner F line counterparts, but show no difference in lean mass or maintenance requirements. These results provide implications about the relationships between the input (intake) and output (maintenance and lean and fat deposition) components of growth.

Three transposable element mutations, displaying an unstable pheno-type at the A locus, were isolated from lines exhibiting Aberrant Ratio behaviour that originated from maize plants treated with plant RNA viruses. Each of these three unstable mutants is shown to belong to the Uq-ruq transposable element system. The two new mutants, along with the previously described a-ruq mutant, are nonautonomous in mutability control in that the control of mutability is governed by the segregating Uq regulatory element. By following the distribution of different Uq elements segregating in independently derived genetic lines and utilizing tests of allelism and linkage, certain lineages of Uq-element-containing lines are revealed.

A new allele of microphthalmia (mi) in the mouse was discovered among the progeny of a male that had been treated with the potent mutagen ethylnitrosourea. Homozygotes have white coats, mildly defective bone resorption and small eyes (about 60% of the normal size) with very little pigmentation. The iris and retina are abnormal, there is no vitreous body and iris pigmentation is restricted to a rim around the pupil. No haematopoietic defect was detected. Genetic studies showed that the mutation is linked to lurcher (Lc) on chromosome 6 and crosses with Miwh/ + and mi/ + mice indicate that the mutation is allelic with these two alleles of the microphthalmia (mi) locus. We designate the new allele microphthalmia-defective iris (midi). Some midi/+ heterozygotes (including the original mutant animal showed a bright ‘red-reflex’ when light was shone directly into the eye and this may have been caused by reduced choroidal pigmentation. Otherwise midi/ + mice appeared normal. The midi/mi compound heterozygotes had white coats, small eyes, and small teeth; bone resorption was more severely defective than in midi/mi homozygotes. The osteopetrosis was corrected by treatment of midi/mi mice with parental mi/ + bone marrow which suggests that the defect is intrinsic to midi/mi marrow cells. The coats of midi/Miwh compound heterozygotes were white; the irises were more symmetrical and iris pigmentation was less severely reduced than in midi/midi homozygotes but pupil dilation appeared to be restricted. Partial complementation occurred in the midi/Miwh compound heterozygotes with respect to eye size, which was usually near normal.