The OTC gene coding for ornithine transcarbamylase is sex linked and subject to X inactivation in humans and mice. We have used a rat cDNA probe to localize OTC by in situ hybridization in marsupials and monotremes. The gene maps to an autosomal site in two distantly related marsupial species and in one monotreme (the platypus); the first demonstration that a gene X-linked in one mammalian species may be autosomal in another. Since the conservation of the mammalian X is thought to be a consequence of its isolation by the inactivation mechanism, we propose that an autosomal or pseudoautosomal segment containing OTC has been recruited into the inactivated region of the X rather recently in eutherian evolution while it remained autosomal, or was translocated to an autosome, in metatherian and prototherian mammals.

A population genetic model is developed and then applied to the synonymous gene sequence variation observed in samples of the Human Immunodeficiency Virus Type 1 (HIV-1). The samples, which were taken from several previous studies, contain sequences of the envelope glycoprotein gene (gp 120) of HIV-1. This analysis suggests that the viral population within an infected patient at any specific time is likely to be composed of close relatives. The viruses in a sample are likely to share a recent common ancestor probably due to consistent positive selection for non-synonymous mutations coupled with low recombination in this region of the genome. There is no substantial difference in synonymous evolutionary rate between samples of sequences obtained from Peripheral Blood Mononucleate Cells (PBMCs) and samples taken from blood plasma. This is likely to be due to the high rate of migration between these 2 HIV sub-populations. The mutation rate for the genetic region examined is estimated at 9·20 × 10−4 per site per month. Under the assumptions of the estimation procedure, this estimate can be bounded between 8·50 and 9·91 × 10−4 with 95% confidence. When coupled with direct estimates of mutation rate, the rate of synonymous evolution suggests that the mean number of generations per month for HIV-1 in vivo is between 1 and 4.

There are a number of reports of gametic disequilibrium between alleles causing segregation distortion (e.g. t alleles in M. musculus and SD alleles in D. melanogaster) and linked loci. These observations have resulted in the conclusion by some researchers that segregation distortion may cause gametic disequilibrium. In this manuscript I have shown that (1) segregation distortion cannot generate gametic disequilibrium de novo and (2) because segregation distortion results in an excess of heterozygotes, the rate of decay of disequilibrium is faster than if segregation distortion were absent. Other factors, such as mutation or selection, appear to generate the observed disequilibrium, and extremely low recombination appears important in retarding its decay.

By crossing a pair of albino strains each with a different adjacent nutritional marker and then crossing the same pair of albino markers with the nutritional markers transposed it was possible to order a series of al mutants with a resolution approaching that available for nutritional markers. A genetic map with approximated distances is provided demonstrating a grouping of mutant sites for a range of discrete carotenoidless phenotypes.

Sexual isolation between the sibling species D. simulans and D. mauritiana is due largely to the rejection of D. simulans males by D. mauritiana females. Genetic analysis shows that genes on the X and third chromosomes contribute to the differences between males causing sexual isolation, while the Y chromosome, second chromosome and cytoplasm have no effect. These chromosome effects differ from those observed in a previous analysis of sexual isolation in hybrid females, implying that different genes cause sexual isolation in the two sexes.

RP4::Mu was used to insert Tn3171 into the Acinetobacter calcoaceticus EBF65/65 chromosome. Insertions occurred at a frequency of approximately 10−7 per recipient cell. Auxotrophic mutations resulted from 28% of the Tn3171 insertions examined, with a possible ‘hot-spot’ for insertion in a gene for arginine biosynthesis. The frequency of subsequent precise excision of Tn3171 from the chromosome was less than 10−10. When attempts were made using RP4 derivatives to mobilize the chromosome from a strain containing an arg::Tn3171 insertion, it was found that the enhanced transfer frequency of the adjacent region of the chromosome was dependent on the original Tn3171 insertion, but was independent of the presence of Tn3171 on the mobilizing plasmid.

Six bacteriophages have been used in the classification of 19 plasmids (antibiotic resistance-mediating R factors and FP sex factors which promote host chromosome transfer) of P. aeruginosa isolated in different geographical regions. On the basis of phage-plating responses on isogenic strains of bacteria differing only in the plasmids carried, five groups of plasmids were distinguishable. In general the groups could be correlated with their geographical origin although differences between plasmids from the same region were found. The unique phage-plating responses were also useful in establishing the possible identity of plasmids isolated from the same original strain and given different designations by independent investigators. The classification of the plasmids derived here on the basis of phage-plating responses could be correlated with classifications based upon other phenotypic characteristics described elsewhere. The nature of inhibition of plating of phages B39 and G101 by R18–1 and R18–3 respectively was shown to be due to interference with some aspect of intra-cellular phage replication rather than to plasmid-mediated restriction.

A model for F-prime formation is presented. It predicts that an Hfr strain giving rise to an F-prime factor would acquire a deletion corresponding to the chromosomal fragment carried by the episome. Genetic studies have confirmed this prediction. Concomitant transfer to the episome of a gene determining a function vital to the cell has permitted selection of derived Hfr strains in which the episomal fragment has been translocated to various sites on the bacterial chromosome.

All four coat hair types were longer in mice homozygous for angora (go / go) than in wild-type mice ( + / +). This increase in hair length in mutant animals was due to an increase in the duration of the phase of hair growth (anagen VI). When skin recombinants incorporating mutant or wild-type epidermis and dermis were grafted to a nude host, the activity of the mutant was found to be confined to the epidermis.

Five class II H-2 genes borne by t chromosomes were partially sequenced: borne by the tTuw10 chromosome of EDY589 (H-2w2); and borne by the tTuw8 chromosome of CR0437 (H-2w57), as well as and borne by the tTuw7 chromosome of CR0435 (H-2w37). These genes are representatives of the three major groups of alleles found associated with t chromosomes. The sequenced part consisted of almost the entire exon 2 and the entire exon 3 coding for the first and the second domain of the β polypeptide chains, respectively. The sequence was compared with the published sequences of Aβ and Eβ alleles borne, by non-t chromosomes. The comparison revealed that the t-associated alleles are no more similar to one another than they are to the corresponding genes present on non-t chromosomes in laboratory mice. This divergence in the nucleotide sequence among the class II genes is interpreted as evidence that the t complex is very old.

The present series of papers is concerned with the variation shown by date of ear emergence, seed weight, and measures of seedling growth rate in the Australian Commercial population of Phalaris tuberosa L. In this first communication, the statistical theory necessary for the interpretation of the available experimental observations is developed. The treatment involves a consideration of the effects of partial self-fertilization under open-pollination, of phenotypic assortative mating, and of maternal effects, on the expectations of the observed covariances among relatives.

Cell lineage analysis of the maroon-like mutation of Drosophila melanogaster revealed the most extensive degree of non-autonomy reported to date in Drosophila: all 1454 gynandromorphs in which X chromosome loss uncovered the ma-l mutation had ma-l+. eye colour. In contrast, among 331 gynandromorphs in which X chromosome loss simultaneously uncovered the vermilion and maroon-like mutations, approximately 16% had v phenotype but with one possible exception all gynandromorphs again had ma-l+ eye colour. These results suggest that very small amounts of the ma-l+ gene product are necessary for wild-type eye colour development and they are therefore compatible with the one cistron–allelic complementation model that has been proposed for the ma-l locus. They also provide the best estimate available to date of In(1)wvc-induced internal mosaicism: 7%. A preliminary attempt to detect DNA-induced transformants among 6 DNA-injected preblastoderm ma-l embryos and at least 80000 of their F1 to F4 descendants has yielded completely negative results. An investigation of the maternal effect which ma-l+ mothers exert on the eye colour of their genetically ma-l offspring revealed that, in contrast to earlier observations, this effect is not universal: some phenotypically ma-l and intermediate ma-l flies were observed in young cultures. The discrepancy between this and earner observations is probably attributable to as yet uncharacterized nutritional deficiencies in the diet of flies used in this experiment. Cytoplasm drawn from blastoderm ma-l+ embryos and injected into the posterior region of ma-l preblastoderm embryos failed to induce eye-colour alterations in all seven flies which survived the treatment. Injection of the contents of embryos of certain genotypes and developmental stages into ma-l pupae 24–48 h old did alter in some instances the eye colour of treated ma-l flies. Various tests strongly suggest that these alterations are not due to injection of a substance that has been stored in the egg during oogensis or that has been produced by the embryo itself prior to injection and they therefore preclude the possibility that a simple in vivo bioassay for the ma-l+ substance has been achieved. Rather, they indicate that the observed eye-colour alterations are due to transplantation of blastoderm-stage embryos which remain active long enough within ma-l hosts to produce and release a substance into the hosts' haemolymph and that this substance in turn induces phenotypic alterations in the hosts' eye colour. When v and ma-l eye colour changes are simultaneously monitored, it appears that injection of embryonic contents into pupae is equally or more effective in modifying the v phenotype than in modifying the ma-l phenotype. Based on these observations, a tentative hypothesis regarding the time of activation of the ma-l+ gene and the relationship between the immediate product of this gene, the maternal substance stored in the egg and the substance released by tissue transplants is proposed.

On the basis of chromosome behaviour in three strains of Drosophila melanogaster males—a wild-type strain, a translocation heterozygote strain and a double translocation strain—it is concluded that the cytologically detected apparent chiasmata in the autosomes are only surface associations of homologous chromosomes and do not involve exchange of chromosome material. Such chiasma-like associations occur also between non-homologous chromosomes. The stainable, Feulgen-positive material of the chromosomes is thought to be responsible for the surface associations.

The resistance (R)-factor R538–1drd of three F-like R-factors tested can cause the transfer of the non-transmissible ColV determinant from E. coli V. The col factor, once transferred to E. coli K-12 strains, was shown to be related to the fertility factor, F, on the basis of entry exclusion and plasmid incompatibility. The col factor was found to recombine with R538–1drd, yielding a transmissible plasmid comprised of the col determinant and the sex factor of the R-factor, but not the resistance genes. The recombinant plasmid was found to be incompatible with both R538–1drd and F, and excluded the entry of R538–1drd but not F.

A strain of S. typhimurium carrying transferable determinants, one for resistance to ampicillin (A), another for resistance to streptomycin and sulphonamides (SSu), was irradiated with ultraviolet light. A clone resulting from this treatment had lost streptomycin resistance and now carried the A determinant and a new determinant, ASu. Except for coding for ampicillin resistance, the ASu determinant was homologous with SSu. The A moiety of ASu produced ampicillin (penicillin) resistance of the same degree as the original A determinant. It was therefore concluded that irradiation had resulted in the elimination of the S gene in the SSu determinant and its replacement by an A gene to form ASu. Experiments with the ASu and SSu determinants suggest that there is normally only one copy of a resistance determinant in the host cell and only one cell site into which it can integrate.