An adenyl cyclase deletion mutant (cya) of E. coli failed to exhibit a heat-shock response even after 30 min at 42 °C. Under these conditions, heat-shock protein synthesis was induced by 10 min in the wild-type strain. These results suggest that synthesis of heat-shock proteins in E. coli requires the cya gene. This hypothesis is supported by the finding that a presumptive cyclic AMP receptor protein (CRP) binding site exists within the promotor region of the E. coli htp R gene. In spite of the absence of heat-shock protein synthesis, when treated at 50 °C, the cya mutant is relatively more heat resistant than wild type. Furthermore, when heat shocked at 42 °C prior to exposure at 50 °C, the cya mutant developed thermotolerance. These results suggest that heat-shock protein synthesis is not essential for development of thermotolerance in E. coli.

Mutations in five loci that modify the phenotype of whiteapricot (wa), caused by the retrotransposon, copia, were examined in two-way combinations to determine whether their effects were additive or epistatic. All two-way combinations of mutations in these five loci, mottler of white (mw), suppressor of forked (su(f)), suppressor of white apricot (su(wa)), Enhancer of whiteapricot, (E(wa)) and Darkener of apricot (Doa), are additive in their effects on wa, implying that each second-site modifier locus affects a different process. Three other copia-induced mutations, HwUa, whd81b25 and ctns were also examined for responsiveness to mutations in these modifier loci. None clearly responded. Mutations associated with B104 insertions, including Gl, vgni, ctn and wric were also examined for responsiveness to mw mutations, which have specificity for this element as well. Both vgni and wric respond to mutations in mw. The former interaction demonstrates that mw is capable of interacting with B104 elements in loci other than white. The significance of the results with respect to the nature of second-site modifier loci is discussed.

We have searched for evidence of historical transpositions of Ac-like sequences in four standard maize lines using the recombinant-inbred mapping technique. Thirty restriction fragments were mapped using EcoR I, EcoR V, and Hind III. The four inbreds contained 24 fragments which mapped to independent sites within each line; the other 6 fragments probably represented multiple mappings of the same element. Possible allelism between lines reduced this number to a minimum of 15 different sites containing Ac-like elements. The distribution of these sequences does not fit the expected Poisson distribution; instead, an unusually large number of these elements were found on chromosome 4. The other sequences were scattered randomly throughout the genome. With few exceptions, each line had sequences in different locations; however, the overall distribution of Ac-like sequences was similar for all lines. The non-random distribution of Ac-like sequences suggests that they have undergone a limited number of transpositions in maize; the distribution is incompatible with either complete immobility or frequent transposition.

A suite of aberrant genetic traits, including increased mutation rate, sex-limited mutation and distorted transmission ratios, was produced among progeny of genetic crosses between two strains of Drosophila mauritiana when a paternally contributed Mos excision factor is placed into a non- Mos genetic background. In the reciprocal cross, involving maternally contributed Mos and Mos associated cytoplasm, the same genetic abnormalities are not observed. Differential effects on mariner excision in germ-line versus somatic tissue are apparent. Because Mos is known to influence the mobility of the mariner transposable element, these traits may be associated with mariner excision and/or transposition.

Five polymorphic proteins, detected by two-dimensional electrophoresis, were analysed in the parents and progeny of a cross between two clones of the malaria parasite Plasmodium falciparum. The information obtained showed that different forms of each protein were determined by allelic variants of each respective gene. One protein was identified as the parasite enzyme adenosine deaminase. Recombinant parasites were produced at a higher than expected frequency.

Several amino-acid synthetic enzymes, belonging to arginie, glutamine, leucine, lysine and phenylalanine biosynthesis, respectively, were investigated under conditions of reduced availability of any one of 16 out of the 20 amino acids represented in proteins. The enzymes showed simultaneous derepression under each condition, albeit to different degrees. Derepression was abolished and the remaining basal enzyme levels reduced by mutations at the cpc-1 locus which governs general amino-acid control in Neurospora. Glutamine synthetase was shown to be under cpc-1 and additional controls. The evidence emphasizes the global nature of general amino-acid control.

This study reports on exceptional males which are obtained by using Drosophila melanogaster mothers carrying the balancers In(l)FM6 or In(l)FM7 as one of their X chromosomes. The phenomenon was first observed in interspecific crosses between D. melanogaster females and males of its closest relatives which normally produce unisexual female hybrid progeny. Whereas hybrid sons from these crosses die as third instar larvae, the presence of the particular X balancers in the mother allows a low percentage of sons to survive. Similar sterile males are also observed among non- hybrid flies. Data are presented which suggest that the males thus generated could be hyperploid for part of their X chromosome as a result of a meiotic event in their mothers or else they could start life as female zygotes and change sex through a mitotic event at an early stage.

Both maternal and zygotic expression of many essential genes are required for normal development. For some of these genes, absence of maternal function yields striking embryonic defects. The experiments reported here examine two questions about such genes: (1) Are embryonic effects of maternal deficits a common property of maternally-and-zygotically active genes? and (2) Is use of the maternal products of these genes restricted to early embryogenesis? A comparison of times of lethality of mutant sons of normal and mutant-heterozygous mothers has been made for six mutations in the zeste-white region of the Drosophila X chromosome. Four of the mutations are defective in single cistrons and two are deficiencies that between them remove thirteen essential loci. All of these mutations had previously been shown to have both maternal and zygotic effects, and all of them had been tested, using homozygous germ-line clones, for the effects of complete maternal defects. For several of them, homozygous germ-line clones cause embryonic defects. Of the six, only one, Df(l)K95, shows a shift from larval to embryonic lethality when the mothers are heterozygous, and even in that case lethality occurs at the very end of embryogenesis. These results have two implications: (1) maternally-derived transcripts do not always serve a solely embryonic role; and (2) an embryonic effect of a complete maternal deficit does not by itself demonstrate an embryo-restricted function for the maternal transcript.

Transmission ratio distortion due to the mouse t complex is thought to be due to harmful effects of trans-acting distorter genes acting on a responder, with the t complex form of the responder being relatively resistant to this harmful action of the distorters. Previous work had indicated that naturally occurring t haplotypes differed in their responders or in distorters lying near the responder, with the result that animals doubly heterozygous for two responder-carrying haplotypes transmitted these haplotypes unequally. In the present work t haplotypes could be divided into three types on the basis of their transmission when doubly heterozygous with the responder-carrying partial haplotype tlowH. The majority, t0, t6, tw1, tw2 and tw73, were transmitted equally with tlowH, a second group, including tw5 and two haplotypes derived from it, were transmitted less frequently than tlowH, and the single member of a third group, t32, was transmitted in excess of tlowH This last result suggests that the underlying differences are in the responder itself, rather than in the distorters. Search for differences among t haplotypes in distorters produced some equivocal results possibly resulting from effects of genetic background. In particular, results of others suggesting presence of a fourth distorter, Tcd-4, were not confirmed.

Segregation Distorter (SD) chromosomes are preferentially recovered from SD/SD+ males due to the dysfunction of sperm bearing the SD+ chromosome. The proportion of offspring bearing the SD chromosome is given the symbol k. The nature of the frequency distribution of k was examined by comparing observed k distributions produced by six different SD chromosomes, each with a different mean, with k distributions predicted by two different statistical models. The first model was one where the k of all males with a given SD chromosome were considered to be equal prior to the determination of those gametes which produce viable zygotes. In this model the only source of variation of k would be binomial sampling. The results rigorously demonstrated for the first time that the observed k distributions did not fit the prediction that the only source of variation was binomial sampling. The next model tested was that the prior distribution of segregation ratios conformed to a beta distribution, such that the distribution of k would be a beta-binomial distribution. The predicted distributions of this model did not differ significantly from the observed distributions of k in five of the six cases examined. The sixth case probably failed to fit a beta-binomial distribution due to a major segregating modifier. The demonstration that the prior distribution of segregation ratios of SD lines can generally be approximated with a beta distribution is crucial for the biometrical analysis of segregation distortion.

The tw5 haplotype is a recessive mutation which is lethal when homozygous in mouse embryos following implantation. This series of studies was undertaken to determine the effect of the tw5/tw5 genotype on embryos developing in vitro. Blastocyst embryos from + / tw5inter se matings were compared with control blastocysts obtained from matings between T/ + and + / + females and + / tw5 males for their abilities to continue development in vitro in two culture media. The data show that there are no significant differences between the percentages of experimental and control blastocyst embryos which attach and outgrow or which contain inner cell masses on any day of culture up to equivalent gestation day 21 in either media. These findings show that the life span of cells from tw5 / tw5 embryos can be extended significantly by in vitro culture.

Chromosome 1 with one or two long insertions has been previously found in natural mouse populations. The inheritance of chromosome 1 with two insertions from the Yakutsk population is analysed in this paper. It was demonstrated that heterozygous females transmit this chromosome to 80–85% of offspring. The observations made at M II, in conjunction with the recombination data, allowed us to conclude that preferential passage of the chromosome 1 with insertions to the oocyte and egg, rather than to the first and second polar bodies at meiosis, is the causative factor of the distorted segregation. A meiotic drive of such potency has not been previously reported for female mammals. The possible mechanism of the drive is discussed.

The chromosomal localization of the mouse gene coding for desmin, one of the muscle-specific intermediate filament subunits, was determined by in situ hybridization using a specific 3H-labelled DNA probe. There is only one copy of the desmin gene and it is located on chromosome 1 in the band C3. This result adds an eleventh locus to a conserved gene cluster and confirms the partial homology that exists between the long arm of human chromosome 2 and chromosome 1 of the mouse.

The mouse mutant curly tail is thought to be inherited as an autosomal recessive (ct/ct) with incomplete penetrance so that approximately 60% of ct/ct individuals exhibit the curly tail (CT) phenotype. By outcrossing ct/ct with mouse stock carrying specific heterozygous combinations of Robertsonian (Rb) chromosomes, trisomy 16 (Ts16) and Ts19 mouse fetuses (and their chromosomally balanced littermates) were derived which were heterozygous for the ct gene. All of the Ts16 (ct/Rb;Rb) fetuses, studied between days 14–19 gestation had tail malformations, 86% of which were tail flexion defects (TFD) apparently very similar to the curly tail phenotype. Neither Ts19 nor any of the chromosomally balanced (ct/Rb) littermates from both experimental crosses showed any type of tail or other spinal malformation. At the 27–29 somite stage of development, Ts16 (ct/Rb;Rb) fetuses did not show any significant delay in the closure of the posterior neuropore (PNP) compared with their littermate controls, suggesting that the tail malformation observed in Ts16 (ct/Rb;Rb) occur as a result of mechanisms which differ significantly from those thought to be responsible to causing the curly tail malformation.

A rare recombinant within the multigenic Hor 2 locus of barley was detected by SD-PAGE of hordein fractions from F2 grain from the cross Bomi × P12/3. Analysis of a homozygous F4 line by 2-D IEF/SDS-PAGE showed that recombination between the class I/II and class III subfamilies of genes had occurred, indicating that they are spatially separate within the Hor 2 locus. RFLP analysis using a B hordein-related cDNA clone confirmed that recombination had occurred, while similar analysis using a genomic clone related to γ-type hordein (encoded by the Hor 5/HrdF locus) indicated the order of the two subfamilies of genes on the short arm of chromosome 5, the class I/II genes being closer to the centromere. The results are consistent with the origin of the B hordein gene family from initial duplication of a single ancestral gene to give two genes which diverged to become the ancestors of the class I/II and class III subfamilies. Subsequent cycles of duplication and divergence have resulted in the present high degree of polymorphism.

Karyotype analysis of a series of established mouse embryonic stem cell (MESC) lines showed that the majority were aneuploid by the 7th and 9th passage and that all lines contained a single Robertsonian (Rb) translocation chromosome with a symmetrical, homologous, arm composition Rb(11.11). Although the chromosomal imbalance makes these MESC lines unsuitable for genetic manipulation in vitro and hence for subsequent production of transgenic animals, the spontaneous occurrence and stable retention of the homologous Rb(11.11) as the only metacentric chromosome in an otherwise all acrocentric karyotype, provides potentially useful cell lines for gene assignment and recombinant DNA studies.

Sperm bearing complete t-haplotypes are preferentially transmitted during fertilization from heterozygous +/t males, often in excess of 95% relative to their +-bearing meiotic partner. Sperm from t-bearing males have an approximate two- to fourfold increase in β1, 4-galactosyltransferase (GalTase) activity, a cell surface protein that mediates sperm binding to the egg zona pellucida. The elevated GalTase activity strictly correlates with the preferential transmission of t-sperm from +/t males, since eight other enzymes show normal levels of activity on t-sperm. Furthermore, sperm bearing proximal partial t-haplotypes, which are no longer favoured during fertilization, have normal levels of GalTase activity. Nevertheless, it has been unclear whether the elevated sperm GalTase activity on t-sperm is due to specific loci in the distal segment of the T/t-complex, or rather, is an indirect consequence of the abnormal sperm function characteristic of +/t and tx/ty males. In this study, it is shown that the elevated sperm GalTase activity is due specifically to factors that reside within the distal segment of the T/t complex, which also contains Tcd-2, the strongest of the distorter loci. Since the structural locus for GalTase is located on mouse chromosome 4, these results also show that T/t-complex alleles on chromosome 17 are regulatory in nature and affect the expression of sperm surface components critical for normal fertilization. Models are presented to explain how elevated GalTase activity could contribute to sperm transmission distortion.

The present investigation primarily deals with the inheritance of a pigmeat quality trait, the Napole technological yield (RTN), a measure of cooked weight to fresh weight. This trait as well as lean percentage at 100 kg liveweight and fattening length from 20 to 100 kg liveweight were recorded on 3459 offspring from 67 sires and 433 dams, and 3052 offspring from 64 sires and 405 dams in Penshire (P66) and Pen Ar Lan (P77) composite lines respectively. The hypothesis of a major 2-allele locus contributing to RTN was tested by use of a segregation analysis method. Highly significant likelihood ratios (mixed vs. polygenic transmission models) lead us to conclude that a major gene RN− exerting an unfavourable effect on RTN is segregating in both lines. Maximum likelihood estimates of the parameters under the hypothesis of mixed (monogenic + polygenic) inheritance show that the difference between the means of the 2 homozygotes amounts to about 3 phenotypic standard deviations of the trait, whereas the complete dominance of RN− cannot be rejected. The frequency of RN− is about 0·6 in both lines. These results are discussed in connection with the previously reported ‘Hampshire effect’ on pigmeat quality, as the Hampshire breed is a common component of the foundation stock of the 2 composite lines under study.

A method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into ‘contribution’ matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size, where N is the number of individuals per generation and μr and are the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing ‘competitiveness’ of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.

The mutation load is sensitive to changes in the segregation ratio caused, for example, by biased conversion. If the distortion, measured by the force of conversion, is greater than the loss of fitness in the mutation heterozygotes, then the mutation load will be far away from its normal value. Examples are given where a small positive bias together with realistic fitness parameters increase the mutation load by more than two orders of magnitude.

In practical terms this implies that great restrictions should be placed on the use of substances and treatments that may induce mutations associated with a positive conversion bias.