A monosome was identified as chromosome 7 of the A genome of the tetraploid cottons by its linkage with the Lc1yg2R2 markers. This makes eight chromosomes of the tetraploids now identified by monosomes. For over a decade the N locus has been considered to be linked with the Lc1yg2R2 loci. Monosomic analysis, however, reveals that N is on a separate chromosome. Studies with a telocentric of chromosome 7 show that the Lc1yg2R2 loci are located in the long arm. It is suggested that the R2 locus rather than the Lc1 locus is in the proximal position. These findings are discussed in relation to data, particularly that involving the linkage group, which supposedly illustrate the compensatory recombination phenomenon in cotton.

A series of derepressed mutants of the tetracycline resistance (T) determinant in R-factor R57 have been found to be repressor-negative and recessive to the T determinant in R6. It is shown that these (Tdr) mutants are dominant to the inducible T determinant in RPl, indicating that the T determinants in R57 and RP1 code for different repressors of the resistance gene. The same Tdr determinants are unstable in cells carrying both the R57 mutant and RP1, probably due to selection against the dominant Tdr gene because it depresses the growth rate of the host cell compared with its T+ homologue. It is suggested that the T determinants giving high-level resistance in R57, R6 and R100 form one homologous group, probably disseminated by the transposon TnlO, while T determinants giving a much lower level of resistance, such as that in RP1, form a separate group, which may include those in R46, and R199. It is proposed that the gene responsible for tetracycline resistance should be designated tetA and the repressor gene tetI. The R57 Tdr mutants then have the genotype tetI−tetA+.

Fifty-one metaphase figures from male Mesocricetus newtoni bone-marrow cells were analysed with respect to the distribution of chromosomes. The peripheral location of the sex chromosomes (XY) and that of the chromosome pairs 3 and 9, as well as the non-peripheral location of the chromosome pairs, 16, 17, 18 was revealed. The significance of the peripheral location of the X chromosome and a possible explanation of the characteristic distribution of the chromosomes are discussed.

Structural genes for the leaf isozymes of peroxidases (E.C.1.11.1.7) have been located on chromosome arms 2BS, 2DS and probably 2AS of wheat, 2RS of cereal rye and on chromosome 2H of Hordeum vulgare. This character provides a useful genetic marker for these chromosome arms, and the results supports the notion of the conservation of gene synteny groups within the Triticinae.

D. melanogaster imagoes were collected weekly throughout the summer and early fall of 1976. Their Adh genotypes were determined by electrophoresis. The frequency of the Adh4 isoallele fluctuated throughout the period of study. Correlation coefficients assuming no delay, one week delay, two weeks' delay, three weeks' delay, and a four-week delay of the effect of temperature on the frequency of the Adh4 isoallele were insignificant. It was concluded that temperature alone may not be a selective factor but may be selective in combination with other environmental factors.

Linkage data for the following markers on chromosome 17 of the house mouse were obtained: centromere (marked by translocation R67), Brachyury (T), tufted (tf), H-2, and thin fur (thf). The markers were found to be arranged in that order in the genetic map and the combined genetic distances between individual markers were found to be as follows: Rb7…T, 4·5 cM; T…tf, 5·8 cM; tf…H-2, 5·0 cM; H-2…thf, 15·1 cM. The localization of the thf locus on the non-centromeric side of the H-2 complex provides an important marker for this arm of chromosome 17. The map distances in the centromeric portion of chromosome 17 changed drastically in the presence of various t factors. These factors strongly reduce the recombination frequency in the T…tf and tf…H-2 intervals and this crossing-over suppression is most likely responsible for the linkage disequilibrium between t and H-2 reported earlier. Recombinants involving a t chromosome but occurring to the right of the H-2 complex do not change the properties of t factors suggesting that all determinants responsible for the t phenotype are located in the chromosomal region between T and tf (H-2).

An effective breeding policy is described for detecting linkage in the mouse, for an ante-natal lethal from crosses of heterozygotes with stocks homozygous for several linked recessive markers. A method of analysing the ensuing data is described, together with a method of estimating the map distance to close markers. A practical illustration is described, involving an ante-natal lethal obtained from a colony of wild mice and a four fold recessive chromosome 2 marker stock.

Starvation for isoleucine inhibits chromosome, minichromosome and pBR322 DNA replication in a stringent strain of E. coli, but does not do so in a relaxed mutant. Starvation for other amino acids inhibits either chromosome and minichromosome replication in both strains. From these results we conclude that oriC and pBR322 replication are stringently regulated and that isoleucine seems not to be essential for the protein synthesis required at the initiation of oriC replication. Deprivation of isoleucine in a Rel− strain gives rise to amplification of minichromosome and pBR322 with a better yield of the latter plasmid than that following treatment with chloramphenicol.

1. A histochemical method has been applied to the detection of alkaline and acid phosphatase mutants in single colonies of Aspergillus nidulans.

2. With the above method it has been possible to isolate mutants in which the alkaline and acid phosphatase activities are affected either separately or simultaneously.

3. Crude extracts of wild-type A. nidulans contain four electrophoretically distinct phosphatase components, two with activity at alkaline pH and two with activity at acid pH. Genes affecting three of the four components have been identified.

4. Two suppressor mutants of an alkaline phosphataseless mutant (palB7) have been isolated. In a strain carrying palB7 and one of these suppressors, the restoration of an alkaline phosphatase component is accompanied by loss of the faster acid phosphatase component. In a similar strain carrying the other suppressor, the partial restoration of the alkaline phosphatase component goes with an electrophoretic alteration of the slower acid phosphatase component.

5. Genetic analysis of twenty-seven mutants has resulted in the identification of fifteen loci affecting the phosphatases. All these loci have been assigned to linkage groups, and twelve of them were also mapped meiotically in relation to other loci.

6. One possible model (based on heteropolymeric proteins) has been proposed to account for the electrophoretic and genetic data on the various phosphatase and suppressor mutations.

The alcohol dehydrogenase (ADH), glutamate oxaloacetate transaminase (GOT), acid phosphatase (ACPH), endopeptidase (EP) and aminopeptidase (AMP) zymogram phenotypes of Chinese Spring wheat, Imperial rye, the Chinese Spring-Imperial triticale and the series of seven disomic Imperial chromosome additions to Chinese Spring were determined. It was found that the zymogram phenotypes produced for one or more of the enzymes by each of the Imperial chromosomes 3, 6, C and D differ sufficiently from that of Chinese Spring so as to provide evidence for the presence or absence of each of these chromosomes in addition lines and triticales. The structural genes Got-R2 and Got-R3 were located in Imperial chromosomes 6 and 3 respectively and other genes involved in the production of GOT in chromosomes C and D. By analysis of GOT alone, evidence for the presence or absence of Imperial chromosomes 3, 6, C and D in addition lines and triticales can be obtained. Adh-R1 was located in chromosome C and a gene(s) involved in the production of an ACPH was located in chromosome D.

The linkages obtained for Got-R2, Got-R3 and Adh-R1 demonstrate homoeology between the Imperial chromosomes 3, 6 and C and the Chinese Spring chromosomes of groups 3, 6 and 4 respectively. The discovery that Adh-R1 is located in Imperial chromosome C also suggests that the 4R/7R and 7R/4R homoeologous groupings proposed elsewhere for the chromosomes of the rye cultivars Imperial, Dakold, and King II should be reassessed, since they are inconsistent with the known linkages of Adh-R1 in the three cultivars. The finding in King II of two forms of ADH and of two ADH genes has been reported. The results of our study of Imperial, King II, and Dakold indicate that rye possesses but one ADH and only one ADH structural gene.

Genetic variation in hormone-sensitive cyclic AMP production was investigated among inbred strains of mice. Significant strain differences were observed in β-adrenergic- and glucagon-stimulated adenylate cyclase activity. Comparable differences were also found in membrane methyl-transferase I activity in these strains. Our results of studies using F1 progeny of high and low strains suggest a dominance of high MT I activity over low MT I activity. Investigation of recombinant inbred lines between the high and low strains indicates that MT I activity is regulated by at least two major genes; H-2-congenic lines of several inbred strains were then used to identify an association between hormone-stimulated MT I activity and the mouse major histocompatibility complex.

The direct and correlated response to selection of scutellar microchaetae and scutellar bristles has been analysed by determining the contribution of the three major chromosomes, alone and in combination with each other, to the overall response. The results of the analysis confirm a previous finding, based on a formal statistical approach, that response to selection for microchaetae had highly pleiotropic effects on scutellar bristles. In lines selected, each for high and low microchaetae, genetic changes in the 2nd and 3rd chromosomes are pre-eminent and essentially equal. Inter-chromosomal interactions are of relatively minor importance in interpreting the response to selection for microchaetae but assume greater importance with respect to the correlated character. The results are discussed in terms of the genetic correlation between fitness and the character measured.