In mice heterozygous for translocation T(2;?)163H, and also for linkage group II markers, the cw locus shows close linkage with the point of rearrangement (about 1−2% recombination). Since T 163 was apparently formed by fusion of two chromosomes near their centromeres, this means that the centromere must lie at the cw end of linkage group II. In homozygotes for T(2; 9)138Ca the genes T and d show significant linkage, indicating that their loci are on opposite sides of the trans-location break. Since, from previous data, the break is known to be proximal to d, it must then be distal to T and, again from previous data, the order of loci hi linkage group IX must be centromere-T-tf-T 138 break.

The genetics of two polymorphic loci in the fowl was studied. Each affects the electrophoretic mobility of a different egg albumen protein, and at each locus two alleles were shown to segregate in a Mendelian manner.

The polymorphic proteins are not any of the well-characterized egg albumen proteins, viz. ovalbumin, ovomucoid, ovomucin, flavoprotein, avidin and lysozyme.

In contrast to all others, two hens were found to have an anomalous, variable, phenotype. A tentative explanation of this was offered.

The charge state model of Ohta & Kimura (1973) for the number of electrophoretically detectable alleles in a finite population, is extended to include mutations of both one and two charge changes. The effective number of alleles (ne) is increased only slightly by this extension. Electrophoretic profiles of neutral variants are shown on average to be leptokurtic and have their odd central moments equal to zero. The expected frequency distribution of pairs of gametes which differ by 1,2,3,… charge units can be obtained as the sum of the appropriate terms from two geometric series.

To analyze abnormal fertilization in a hereditary mosaic strain (mo/mo) of Bombyx mori, the percentages of diploidy mosaic, polyploidy mosaic and polyploid eggs in a batch were estimated by using egg colour mutants (pe re). Among 48 890 eggs from crosses of pe + / + re, mo/mo females with pe re/pe re males, 9409 abnormal eggs were obtained; 4472 of them were diploidy mosaics (red-white eggs), 4038 were polyploids (black eggs) and 899 were polyploidy mosaics (566 black-white, 256 black-red and 77 black-white-red eggs). The total number of diploidy mosaic eggs was approximately equal to that of polyploid eggs. A significant correlation was detected between the diploidy mosaic and polyploid egg ratios within a batch. This suggests that diploidy mosaics are produced by double fertilization in which two genetically non-identical egg nuclei are fertilized in turn by a sperm, and polyploids are formed by the fertilization of a diploid, non-disjunctive egg nucleus gamete by a single sperm. Our results also indicated the presence of common factors modifying both mosaic and polyploid frequency. The concordance of the observed ratio of polyploidy mosaic eggs (1·84%) with the expected value (diploidy mosaic ratio × polyploidy ratio × 2 = 1·83%) suggests that the formation of mosaics occurs independently of the formation of polyploids in this abnormal fertilization process. We point out that it is necessary to modify Goldschmidt & Katsuki's general model to explain abnormal fertilization, and we propose several possible models.

Tetrad data from short gene-marked intervals provide information on the frequency of multiple exchanges within intervals. Non-parental ditype and tetratype frequencies from 58,000 interval-tetrads of Neurospora crassa show that 4-strand double exchanges are far less frequent than would be expected in the absence of chiasma or chromatid interference. These results are in general agreement with meiotic tetrad data from other organisms, except Aspergillus nidulans. They preclude the occurrence of reciprocal meiotic exchanges as clusters unless multiples within each cluster are restricted so as not to involve all four chromatids. If this is not the case, and chromatid interference does not occur, then chiasma interference must be strongly positive within short regions. Known cases of apparent negative interference among random meiotic segregants are probably the result of non-reciprocal conversion of a middle marker, rather than of multiple reciprocal crossing over.

In view of the exceptional usefulness of Drosophila hydei for the analysis of Y-chromosome activity, a technique has been developed which permits the production of large numbers of males lacking a Y chromosome. It is based on the synthesis of new compound(1) chromosomes which carry sufficient rDNA genes to secure survival in the absence of any Y-chromosomal rDNA. Through non-disjunction in males of suitable stocks, fertile Compound(l) females which lack the Y chromosome, phenotypically distinguishable from their normal sibs, are produced in sufficient number to allow the subsequent breeding of X/O males in gram quantities for biochemical studies.

Mutants of Chinese hamster ovary (CHO) cell resistant to cytosine arabinoside (ara-C), an inhibitor of DNA synthesis and antitumour drug, have been isolated and characterized both biochemically and genetically. Mutants occurring spontaneously and those induced by treatment with N-methyl-N′-Nitro-N-nitrosoguanidine (MNG), were obtained at a frequency of 0·24 × 10−6 and 3·4 10−6 respectively. The mutants showed a stable ara-C resistant phenotype which was inherited as a dominant trait in genetic crosses. The wild type (CHO K-1) and the mutant (103, 002 and 003) cells showed no differences in the levels of the uptake of ara-C or of its degradation. Results of biochemical studies further excluded the involvement of deaminase, kinase and ribonucleotide reductase as the possible factor(s) in conferring drug resistance to the mutant cells. However, the wild type and mutant DNA polymerases differed in the level of the in vitro incorporation of specific dNMP in the presence of ara-CTP. These data suggested that the wild-type DNA polymerase which becomes error prone in the presence of ara-CTP may cause the drug sensitivity of the wild-type cells and that a change in the mutant enzyme making it resistant (or less prone) to ara-CTP induced errors in dNMP incorporation may control the drug resistance of the mutant cells.

Wright proposed that there is a ‘shifting balance’ between selection within demes, random drift, and selection between demes at different ‘adaptive peaks’. We investigate the establishment and spread of new adaptive peaks, considering a chromosome rearrangement, and a polygenic character under disruptive selection. When the number of migrants (Nm) is small, demes fluctuate independently, with a bias towards the fitter peak. When Nm is large, the whole population can move to one of two stable equilibria, and so can be trapped near the lower peak. These two regimes are separated by a sharp transition at a critical Nm of order 1. Just below this critical point, adaptation is most efficient, since the shifting balance greatly increases the proportion of demes that reach the global optimum. This is so even if one peak is only slightly fitter than the other (ΔW≈1/N), and for both strong and weak selection (Ns (Ns ≪ 1 or Ns ≫ 1). Provided that Nm varies sufficiently gradually from place to place, the fitter peak can be established in regions where Nm≈1, and can then spread through the rest of the range. Our analysis confirms Wright's argument that if selection, migration and drift are of the same order, the ‘shifting balance’ leads to efficient evolution towards the global optimum.

Restriction site analysis revealed a variant growth hormone gene haplotype fixed within growth-selected mice (High line-3; HL-3) exhibiting growth rates 1·5 times greater than those of unselected Foundation population (FP-3) mice. Relative to the FP-3 haplotype, the HL-3 haplotype exhibited restriction fragment length polymorphisms for each of seven different restriction enzymes. Three of the polymorphic sites lie within 1·1 kb of the 5′ end of the structural gene; a fourth polymorphism exists within the structural gene. The HL-3 haplotype was also fixed within an additional three growth-selected lines (including a replicate of HL-3). This identification of an association, between the natural variant of a growth regulating gene and a growth-related phenotype, is the prototype of experiments that could lead to the isolation of variant genes which enhance livestock production characters.

Wild-type cells of Aspergillus nidulans have undetectable NADL-glutamate dehydrogenase activity when utilizing glucose and high levels of NAD L-glutamate dehydrogenase when utilizing certain amino acids as sole carbon sources.

A mutant, designated gdhCl, has appreciable NAD-GDH activity when utilizing glucose as a carbon source. The gdhC1 mutation is semi-dominant and is located in linkage group III.