The genetic relationship between germspores and parental mycelia has been investigated in crosses involving multiply-marked heterokaryons and in simple difactor crosses.

It is concluded that for each zygospore the number of different diploid nuclei undergoing meiosis is often more than one, but generally not more than two. The meiotic products divide to produce the nuclei in the usually uninucleate germspore primordia and then continue dividing to produce germspores. Unmated nuclei do not pass directly from parents to progeny.

Each germsporangium contains differing numbers of viable germspores, with an average of about 7000; different genotypes are represented by varied numbers of germspores and often expected genotypes are missing. When the results of several germsporangia are added together or germspore stocks from many germsporangia are analysed, reciprocal genotypes appear in equal numbers and reliable recombination frequencies may be calculated.

We have constructed a linkage map of random amplified polymorphic DNAs (RAPDs) in Bombyx mori. We screened 320 10-mer primers, and found 243 clear polymorphic bands between C108 and p50 strains. In the F2 generation, segregation ratios of 168 bands were nearly 3:1 in a chi square test, showing Mendelian inheritance. The MAPMAKER program sorted 168 bands into 29 linkage groups and 10 unlinked loci at minimum LOD score 3·0, and determined orders of loci in each group, which contained 2–11 markers. It also detected typing errors in our data. We calculated map distances between pairs of neighbouring loci using recombination values in males and the Kosambi mapping function. Our RAPD map consists of 169 loci including the p locus, and the sum of map distances is approximately 900 cM. Linkage groups 1 and 2 of our map correspond to chromosomes 1 and 2 on the conventional linkage map because of linkage to sex and p, respectively.

Bacteriophage εγ is capable of transduction both by replacement of a genetic segment of the recipient by the homologous genetic material from the donor strain and by the formation of defective transducing particles capable of lysogenizing the recipient strain of S. anatum.

The isolation of strains carrying such prophages, which have incorporated the lactose or arabinose operons, is reported. Lysogenic strains, carrying both normal and defective transducing prophage, form high-frequency transducing lysates. Other strains, carrying only defective prophage, show evidence that the association of prophage genes and transduced materials is stable since the loss of one frequently entails loss of the other.

1. A mild diabetes insipidus is associated with the oligosyndactyly caused by the dominant gene Os. No recombinants were observed between the diabetes and the oligosyndactyly so the diabetes is probably a pleiotropic effect of the Os gene.

2. There are one or more modifying genes which in combination with Os enhance the manifestation and cause a severe diabetes insipidus. This affects both sexes and becomes progressively worse in older animals, the average water intake reaching 50–60 ml. per 24 hours, or 1·7 times the body weight.

3. The modifying gene or genes, in the absence of the Os gene, themselves produce a mild diabetes insipidus, which becomes severe in some old females.

4. The severe diabetes insipidus associated with Os and the modifying genes together is probably renal in origin.

A formula for effective population size when fertility is inherited is worked out. It is shown that the effective size decreases as the heritability of fertility or progeny number increases.

An analysis based on a model that is different from the traditional Fisher's model for quantitative characters under assortative mating reveals that the genotypic offspring–midparent regression can be affected by assortative mating of parents. It is demonstrated that the prediction that mating parents assortatively introduces only a negligible bias in the estimated coefficient of linear offspring-midparent regression is limited to Fisher's model and cannot be generalized.

The TOL(M1) metabolic plasmid was transferred from Pseudomonas arvilla mt-2 to a mutant of Pseudomonas putida. Although neither the donor nor the recipient could grow on phenol, the transconjugants could grow slowly on this carbon source. In these transconjugants phenol was converted to catechol by chromosomal encoded phenol hydroxylase followed by degradation of catechol by low uninduced levels of the plasmid encoded catechol meta cleavage pathway. A mutant, which grew well on phenol, was isolated from one of the transconjugants and it was found that phenol could now act as an inducer for the meta cleavage pathway.

In the present study, skin fibroblasts and leukocyte cultures from patients with acute infectious mononucleosis were examined to determine if any in vitro marker chromosomes could be detected. No alterations in chromosomes could be found in fibroblasts either from the region of the typical rash or from other areas of skin. This would tend to suggest but does not necessarily prove that this tissue was not extensively involved in the disease process.

In order to develop a system for the study of the mechanism of intragenic recombination in Ustilago, mutants lacking nitrate reductase activity were isolated, and five alleles were combined in pairs in ten vegetative heteroallelic diploids. The diploids have the mutant phenotype, i.e. inability to utilize nitrate as sole source of nitrogen, but they will recombine to produce wild-type cells much more frequently than the back-mutation rates of haploids or homoallelic diploids. The spontaneous rate of recombination can be enormously increased by low doses of UV light, particularly if treatment is during the period of DNA synthesis in the mitotic cycle. By means of half-tetrad analysis it has been shown that this process of intragenic recombination, as in other fungi, is due to gene conversion rather than reciprocal exchange. It has also been shown that the frequency of UV-induced conversion under standard conditions gives a rough measure of the distance between two mutant sites, since it was possible to use these frequencies to make a linear fine structure map of the gene. These results are discussed in relation to a hybrid DNA model for gene conversion slightly modified from that previously suggested for meiotic recombination.

A method for concentrating flagella-paralysed (mot−) cells existing in a large number of non-flagellated cells of Salmonella was invented. The mot− cells expressing the phase-1 flagellar antigen i were agglutinated by anti-i serum with carriers, the dead cells of TM2 expressing the phase-1 antigen i; only the agglutinated cells were harvested by a low speed of centrifugation and incubated in broth. About tenfold concentration was brought about by one treatment, which was repeated for further concentration. By this method, the motA257 motC244 double mutant which was produced by transduction at a frequency of about 3 × 10−6 per non-flagellated recipient cell was isolated from the broth culture concentrated five times, in which about 30% of the cells were the double mutant.

Previous measurements of specific locus mutation rates in mice had all involved the seven loci, a, b, c, d, p, s and se. An experiment was performed with the same mouse stock (C3H × 101) and the same radiation dose (600 rad) to spermatogonia as had been used previously, but employing a new group of six loci, a, bp, fz, In, pa and pe. The observed mutation rate, 5·0 × 10−8 per locus per rad, was significantly lower than that for the original seven loci, but was three to four times higher than the corresponding mutation rate in Drosophila melanogaster.

If heterozygotes for a reciprocal translocation are intercrossed, some of their viable balanced progeny result from the fusion of unbalanced gametes with complementary duplications and deficiencies of the translocated segments. Therefore, if one parent in such an intercross is homozygous for a genetic marker on one of the segments concerned, some homozygous offspring will be produced even if the other parent does not have the marker. The expected frequency of such exceptional offspring among live-born is one-sixth if the marker is on the distal (non-centromeric) side of the point of exchange and single chiasmata normally occur in each interstitial segment. Much lower frequencies are expected if the marker is on the centromeric side, since duplications and deficiencies of proximal segments occur only as a consequence of adjacent-2 disjunction, in which homologous centromeres proceed to the same pole. This is rarer than normal disjunction. Thus, by comparing the frequencies of offspring homozygous for markers on one or other side of the point of exchange, it is possible (i) to determine which marker is in the centromeric segment, (ii) to estimate the frequency of adjacent-2 disjunction, given information on the nature of meiotic configurations in the translocation concerned.

By this method, it is shown that the frequency of adjacent-2 disjunction is similar in heterozygotes for mouse translocations (T5;18)26H, T(13; ?) 70H and T(14;17)264Ca, averaging 13%. Centromeres were located at the Sd end of linkage group V (confirming previous findings), the fz end of XIII and the bg end of XIV.

Adult Drosophila males were injected with chloroethyl methanesulphonate and late progeny, tracing back to treated spermatogonia, were examined for sex-linked lethals and for translocations involving the X, Y, second and third chromosomes. A dose yielding about 20% sex-linked lethals produced 11 translocations in about 3500 tested chromosome sets (approx. 0·3%). This result is discussed in relation to the problem of chromosome rearrangements in different germ-cell stages.

Lysis of stock 7 killers with ½% sodium deoxycholate, yields preparations with one half as much killing activity as homogenates, while lysing virtually all of the bright particles known to have killing activity in homogenates. The killing activity which persists is associated with particles which sediment at the same rate as the refractile bodies, the only visible remnant of the bright particles. It is concluded that killing activity is probably associated primarily, if not exclusively, with the refractile bodies of the bright kappa particles. Partially purified killer particles when stored at 27° C. for more than one day, progressively lose their ability to produce spinning of sensitives but retain their ability to produce paralysis. Loss of activity in crude preparations of refractile bodies kept 2 hours at 31° C. can be retarded by homogenates of either killers or sensitives.