bluuebunny/crossref_metadata_2025 huggingface dataset:
Implications of the genetic divergence between European wild mice with Robertsonian translocations from the viewpoint of mitochondrial DNA
Authors: Moriwaki Kazuo , Yonekawa Hiromichi , Gotoh Osamu , Minezawa Mitsuru , Winking Heinz , Gropp Alfred
Published: September 2009

Genetic divergences between the wild mouse populations with various Robertsonian translocations from the Poschiavo Valley, Yugoslavia, Milan and the Apenninies, were estimated based on the mitochondrial (mt) DNAs. The mtDNAs isolated from the liver were analysed by agarose slab-gel electrophoresis after digestion with eight kinds of restriction endonucleases: BamHI, EcoRI, HindII, HindIII, PstI, HpaI, HpaII and BgII. These preparations were further used to make restriction maps, from which sequence divergence between each Rb variation was calculated to be 0·2–2·2%. These rather larger values appear to be in conflict with the present concept that the Rb variations occurred during the last several thousand years. Both, however, might be reconciled by assuming genetic introgression of the founder with a small number of Rb translocations into other subspecies populations genetically remote and the subsequent rapid accumulation of Rb translocations unique to each population due to an unknown mechanism occurring specifically in the intersubspecies hybrids betweenM. m. domesticusand the otherM. m. subspecies. This was the case also in a new Rb (9.15) translocation obtained from Ogasawara Islands in Japan which was the intersubspecies hybrid betweenM. m. molossinusandM. m. domesticus.
Chloroplast DNA diversity in wild and cultivated barley: implications for genetic conservation
Authors: Clegg M. T. , Brown A. H. D. , Whitfeld P. R.
Published: September 2009

Nine diverse lines of cultivated barley (Hordeum vulgare) and 11 lines of its wild progenitor (H. spontaneum) were assayed for variation in their chloroplast DNA by digestion with ten restriction endonucleases. The cultivated lines exhibited a single cpDNA polymorphism, whereas the wild material exhibited five. The significantly lower level of diversity among the cultivated lines was unexpected because both cultivated and wild lines had been selected for comparable levels of diversity for nuclear encoded isozyme loci. These results suggest that the level of cytoplasmic diversity was markedly restricted during the domestication of cultivated barley.
Hybrid dysgenesis inDrosophila melanogaster: partial sterility associated with embryo lethality in theP-Msystem
Authors: Kidwell Margaret G.
Published: September 2009

Variable frequencies of unhatched eggs were observed to be produced by a number of F1interstrain hybrids. This type of partial sterility resulting from F2embryo death was found to be associated with theP-Msystem of hybrid dysgenesis. Dysgenic hybrid progeny of crosses betweenMstrain females andPstrain males may therefore have reduced fertility due to the disruption of development at two different stages: early F1gonadal development and early F2embryo development. These disruptions result in the previously described F1gonadal dysgenesis (GDsterility) and F2embryo lethality (ELsterility) respectively. The two morphologically distinct types ofP-M-associated sterility differ in their patterns of response to F1developmental temperature, and the temperature-sensitive period forELsterility occurs considerably later in F1development than forGDsterility.ELsterility is similar toSFsterility, which is associated with theI–Rsystem of hybrid dysgenesis in that both result from death during early F2embryogenesis. However,ELsterility differs fromSFsterility in not being restricted to hybrids of the female sex and in showing different patterns of response to temperature and ageing in the F1generation. Some implications of the existence ofELsterility for methods of strain classification in theI–Rsystem are explored.
Polymorphism of t-complex genes in European wild mice
Authors: Klein Jan , Sipos Peter , Figueroa Felipe
Published: September 2009

Thirty-two t haplotypes were extracted from wild mice captured in Central Europe, Spain, the Soviet Union, Israel, Egypt, the Orkneys and South and North America, and tested for lethality in the homozygous state. Twenty-two proved to be homozygous lethals, 8 semilethals and 2 viables. The lethal t haplotypes were then tested by the genetic complementation test for identity with representatives of known complementation groups and with each other. Five of the 22 haplotypes proved to carry previously identified lethality factors (tw5, tw73, and tLub-1), while the rest carried new factors. The 17 haplotypes fell into 8 new complementation groups. Two of the new groups are partially overlapping in that they seem to share some lethality factors and differ in others. These tests raise the total number of known complementation groups to 16. The distribution of the individual t haplotypes among wild mice populations seems to reflect their differentiation from a common ancestor haplotype.
Effects of selection on growth, body composition and food intake in mice: II. Correlated responses in reproduction
Authors: Brien Forbes D. , Sharp Gillian L. , Hill William G. , Robertson Alan
Published: September 2009

Female reproductive performance is reported in mice selected for ten generations for one of three criteria: either appetite (A), fat percentage (F) or total lean mass (P). For each criterion lines were selected for high (H) or low (L) performance, with contemporary unselected controls (C). In theAandPlines, litter size changed in the direction of the selected criterion, the changes being larger and more rapidly established in theAthan in thePlines. At generation 10, the differences in litter size between high and low lines were 2·6 live young born in theAlines, and 1·0 live young born in thePlines. The differences in 6-week weight between the high and low lines were 3·5 g in theAlines, 6·5 g in thePlines. Changes in ovulation rate were the primary reason for changes in litter size, the differences between the high and low lines being 3·8 corpora lutea for theAlines, and 3·1 corpora lutea for thePlines. Fitting body weight at mating as a covariate within lines in the analysis of ovulation rate and live foetus number removed the differences between the high and low selectedPlines, but not those in theAlines. The high and low selectedAandPlines did not differ in prenatal survival. There were no consistent differences in litter size, ovulation rate or pre-natal survival in theFlines.
Multilocus recombination frequencies
Authors: Morton N. E. , MacLean C. J.
Published: September 2009

Multilocus recombination frequencies are expressed in terms of pairwise recombination frequencies for paracentric and pericentric intervals. Applications of this theory to mapping and genetic counselling are discussed.
Mapping of the genes controlling high-molecular-weight glutelin subunits of rye on the long arm of chromosome 1R
Authors: Singh N. K. , Shepherd K. W.
Published: September 2009

The gene(s) controlling the high-molecular-weight glutelin subunits in rye (designated asGlu-Rl) was mapped with respect to the centromere using a 1RL-1DS wheat-rye translocation line and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Analysis of 479 seeds from test-crosses between a 1R/1RL-1DS heterozygote and the cultivar India 115, revealed 14·6% aneuploid and 3·95% recombinant progeny. Excluding the aneuploids, this locus was calculated to be 4·65 ± 1·04 cM from the centromere on the long arm of chromosome 1R, which is comparable to the position of the homoeologous loci in wheat and barley.
Inheritance of female mating propensities foryellowlocus genotypes inDrosophila melanogaster
Authors: Heisler I. Lorraine
Published: September 2009

Females from different wild-type laboratory populations ofDrosophila melanogasterdiffer genotypically in their degree of mating discrimination against mutantyellowmales. The chromosomal organization of this difference was examined in two wild-type laboratory strains by experimental observation of the mating propensities of hybrid females in a mass-mating, multiple choice situation. The results indicate that the strain difference is polygenic in origin, involving loci on both theX-chromosome and autosomes. Reciprocal crosses revealed no maternal/cytoplasmic effects. The mating scores of parental, F1and backcross females fit well to a model of additive chromosomal effects, withX-linked loci being recessive, and autosomal loci overdominant, for increased mating withyellowmales. However, interactions, arising most probably from recombination, led to increased mating withyellowon the part of F2females. In addition to the difference in female discrimination againstyellowmales, male/female interaction was found for the mating speed of flies from the two strains. These results are discussed in the light of previous studies of mating preferences inD. melanogaster. It is suggested that genetic variation in female mating preferences may be an important source of variation in the reported mating success of mutantyellowmales.
The genetics of tasting in mice: III. Quinine
Authors: Lush Ian E.
Published: September 2009

Twenty-nine strains of mice were tested for their ability to taste a 0·8 mM solution of quinine sulphate. There were large strain differences, some strains (tasters) showing a strong aversion to the quinine and other strains (non-tasters) showing very little aversion. It was shown that the difference between strains 129/Sv and A2G is probably due to one gene. By using the CXB RI strains it was also shown that the difference between C57BL/6By and BALB/cBy is probably due to one gene. It is suggested that both differences may be due to the same gene, named Qui. In the progeny of a backcross involving both Soa and Qui there was evidence of an interaction between the genes which cannot be explained satisfactorily. Learning behaviour by the mice influenced their drinking habits, but this did not invalidate the results.
A presumed deletion covering theWandPhloci of the mouse
Authors: Lyon Mary F. , Glenister P. H. , Loutit J. F. , Evans E. P. , Peters J.
Published: September 2009

A new allele at theW-locus (W19H), found in a mutagenesis experiment in which females were irradiated, involves a presumed deletion. The deletion covers thePhlocus (which forms part of a gene complex with theW,PhandRwloci), and the locus of a recessive lethal 2 cM distal toW. It does not extend distally to thebllocus; nor does it involve theRwlocus,W19H/Rwcompounds being viable and fertile. Thus, the length of the deletion is 2–7 cM. The non-involvement ofRwshows that, in the gene tripletRw,W,Ph,Rwmust lie proximal toWandPh, whose relative position remains unknown. Heteozygotes forW19Hare not anaemic, show only minimal white spotting and no pigment dilution; they thus resemble heterozygotes for the originalWmutant allele and differ fromW/Phtrans heterozygotes, which have extensive white spotting. In additionW19Hheterozygotes may be small and runted, many are believed to die prenatally, and some in the nest. Their radiosensitivity is increased. Homozygotes die at the pre-implantation stage.
Deleterious mutations as an evolutionary factor: 1. The advantage of recombination
Authors: Kondrashov Alexey S.
Published: September 2009

A population withudeleterious mutations per genome per generation is considered in which only those individuals that carry less than a critical number ofkmutations are viable. It has been shown previously that under such conditions sexual reproduction is advantageous. Here we consider selection at a locus that determines recombination frequency of the whole genome. The valuev=u/ √khas been found to play the decisive role. Whenv< 0·35 the direction of selection for recombination may be different for different cases, but the intensity of selection is always very small. The advantage of recombination becomes considerable whenv> 0·5, its growth under increasingvbeing approximately linear. Ifv> 2 no less than 95% of the progeny are bound to die because of the selection against deleterious mutations. Since this seems to be too great a mutation load, we may assume 0·5 < v < 2·0 for any sexual population if mutation really maintains crossing-over. Results on selection at a locus which controls mutability provide evidence thatvis located within the specified interval if the physiological cost of a twofold reduction of the mutation rate is within the range 10–80%. A number of consequences of this hypothesis about the mechanism of selection for sex and recombination are discussed.
Genetic relationships between inbred strains of rats. An analysis based on genetic markers at 28 biochemical loci
Authors: Festing Michael F. W. , Bender Klaus
Published: September 2009

Genetic similarities among 46 strains of rats based on published data involving 93 samples and 28 biochemical loci were assessed using principal coordinate and cluster analysis techniques. Seventeen strains were represented by more than one colony. In ten of these, nominally identical strains differed, and in four cases this was attributed to genetic contamination. A total of 52 genetically different strains were eventually identified. Strains BN and DA were most dissimilar, while strain BP was the most unusual strain over-all. The principal coordinate and cluster analysis showed three main clusters, which could be explained on the basis of linkage disequilibrium for some of the esterase loci in linkage group 5. Among six of these loci only 12 haplotypes were observed, with 24/52 strains having a single haplotype. Re-analysis of loci in linkage equilibrium failed to reveal any important clusters.
Genetic differences between two substrains of the inbred 101 mouse strain
Authors: West John D. , Peters Josephine , Lyon Mary F.
Published: September 2009

Two substrains of the inbred mouse strain 101, maintained at Harwell and at Neuherberg, and designated 101/H and 101/E1, differed at five of the eight genetic loci tested and it seems very likely that one of these substrains has been genetically contaminated. The available evidence suggests that 101/E1 is probably the contaminated substrain.
Sex ratio distortion in D. simulans after treatment with quinacrine
Authors: Tsakas S. C. , Lamnisou K. , Tsacas L. , David J. R.
Published: September 2009

A significant excess of female offspring resulted when pregnant females of the D. simulans species were left to lay their eggs on food containing quinacrine. The same result occurred in a subsequent experiment in which male parents were injected with quinacrine. This was the first time that a chemical compound showing an affinity with DNA in vitro altered the sex ratio in a consistent manner. This effect had been predicted based on the unique quinacrine fluorescent staining pattern in D. simulans, in which only the Y stains intensely in mitotic chromosomes. It seems that treatment acts on spermatids or spermatozoa causing decreased functioning of the Y-bearing ones, resulting in an excess of female offspring. Interestingly, the species D. mauritiana and D. melanogaster, although very closely related to D. simulans, do not have its staining pattern and as predicted did not respond to treatment; therefore, the important parameter appears to be related to the staining pattern of mitotic chromosomes and not to the phylogenetic relationship.
Distorter genes of the mouset-complex impair male fertility when heterozygous
Authors: Lyon Mary F.
Published: September 2009

Male mice heterozygous for two distorter genes,Tcd-1andTcd-2, of the mouset-complex but homozygous wild type for the responder, were generated by crossing animals carrying the partialt-haplotypesth51andth18to inbred strains. The fertility of these males was then compared with that of their brothers carrying normal chromosome 17s. On three of the inbred backgrounds used, C3H/HeH, C57BL/6J and TFH/H, theth51th18+ / + + + males were significantly less fertile than their normal sibs. With the fourth inbred strain used, SM/JH, both types of male were nonnally fertile. This confirmed earlier preliminary findings that when both homologues of chromosome 17 carry wild-type alleles of the responder, heterozygosity for the distorter genes is sufficient to impair fertility, but the effect varies with genetic background. These results are consistent with the concept that both the transmission ratio distortion and the male sterility caused by thet-complex are due to harmful effects of the distorter genes on wild-type alleles of the responder.
α-Amylase and β-amylase homoeoloci in species related to wheat
Authors: Ainsworth C. C. , Miller T. E. , Gale M. D.
Published: September 2009

A study of α-amylase isozyme patterns from gibberellin-induced endosperms of wheat-alien genotypes (amphiploid, addition and substitution lines) resolved by flat-bed isoelectric focusing identified homoeoloci for α-Amy-1(malt α-AMY-1 genes) on chromosomes 6H ofHordeum vulgare, 6RL ofSecale cereale, 6RmofS. montanumand 6E ofAgropyron elongatum. Homoeoloci for α-Amy-2(green α-AMY-2 genes) were identified on chromosomes 7HchL ofHordeum chilense, 7RL ofSecale cereale, 7SbofAegilops bicornis, 7U ofAe. umbellulataand 7EL ofAgropyron elongatum. Analysis of mature grain β-amylase identified β-Amy-1loci on chromosomes 4H ofH.vulgare, 4HchofH. chilense, 4S1ofAe. sharonensisandAe. longissimaand β-Amy-2loci on chromosomes 5RL ofS. cerealeand 5U ofAe. umbellulata. These gene locations provide further evidence for the homoeology of the alien chromosomes with wheat and for the conservation of gene synteny among wheat and its relatives.
Caffeine-resistant mutants ofCaenorhabditis elegans
Authors: Hartman Philip S.
Published: September 2009

Wild-typeCaenorhabditis elegansfails to reach adulthood if L1 larvae are incubated in the presence of 30 mM or greater concentrations of caffeine. Eleven mutants have been isolated in which caffeine has a less pronounced effect on development. The mutations are recessive, define two genes, and have been mapped. The mechanism(s) of resistance is unknown.
Accumulation of mutations in sexual and asexual populations
Authors: Pamilo Pekka , Nei Masatoshi , Li Wen-Hsiung
Published: September 2009

The accumulation of beneficial and harmful mutations in a genome is studied by using analytical methods as well as computer simulation for different modes of reproduction. The modes of reproduction examined are biparental (bisexual, hermaphroditic), uniparental (selfing, automictic, asexual) and mixed (partial selfing, mixture of hermaphroditism and parthenogenesis). It is shown that the rates of accumulation of both beneficial and harmful mutations with weak selection depend on the within-population variance of the number of mutant genes per genome. Analytical formulae for this variance are derived for neutral mutant genes for hermaphroditic, selfing and asexual populations; the neutral variance is largest in a selfing population and smallest in an asexual population. Directional selection reduces the population variance in most cases, whereas recombination partially restores the reduced variance. Therefore, biparental organisms accumulate beneficial mutations at the highest rate and harmful mutations at the lowest rate. Selfing organisms are intermediate between biparental and asexual organisms. Even a limited amount of outcrossing in largely selfing and parthenogenetic organisms markedly affects the accumulation rates. The accumulation of mutations is likely to affect the mean population fitness only in long-term evolution.
Adaptive landscapes, genetic distance and the evolution of quantitative characters
Authors: Barton N. H. , Turelli Michael
Published: September 2009

The maintenance of polygenic variability by a balance between mutation and stabilizing selection has been analysed using two approximations: the ‘Gaussian’ and the ‘house of cards’. These lead to qualitatively different relationships between the equilibrium genetic variance and the parameters describing selection and mutation. Here we generalize these approximations to describe the dynamics of genetic means and variances under arbitrary patterns of selection and mutation. We incorporate genetic drift into the same mathematical framework.

The effects of frequency-independent selection and genetic drift can be determined from the gradient of log mean fitness and a covariance matrix that depends on genotype frequencies. These equations describe an ‘adaptive landscape’, with a natural metric of genetic distance set by the covariance matrix. From this representation we can change coordinates to derive equations describing the dynamics of an additive polygenic character in terms of the moments (means, variances, …) of allelic effects at individual loci. Only under certain simplifying conditions, such as those derived from the Gaussian and house-of-cards approximations, do these general recursions lead to tractable equations for the first few phenotypic moments. The alternative approximations differ in the constraints they impose on the distributions of allelic effects at individual loci. The Gaussian-based prediction that evolution of the phenotypic mean does not change the genetic variance is shown to be a consequence of the assumption that the allelic distributions are never skewed. We present both analytical and numerical results delimiting the parameter values consistent with our approximations.
Antisuppressor mutations inAspergillus nidulans: cold-resistant revertants of suppressorsuaC109
Authors: Martinelli S. D.
Published: September 2009

Cold-resistant revertants of the cold-sensitive, ribosomal suppressorsuaC109have been isolated, with a view to obtaining mutations in new ribosomal protein genes. Many revertants had reduced suppressor activity and were classified as antisuppressor mutants. Both intragenic and extragenic reversions were found. In seven strains the extragenic reversion to cold resistance segregated with the antisuppressor phenotype, and these were designatedasumutations. Three of the fiveasugenes, C, B and D were mapped to linkage groups, I, II and V respectively. The antisuppressors are not gene-specific, although they mainly antagonize the activity of ribosomal suppressors. The antisuppressors altered all aspects of the phenotype of suppressorsuaC109including sensitivity to aminoglycoside antibiotics, and are therefore thought to be mutations in ribosomal protein genes.
Inheritance of alleles at ten enzymatic loci of the freshwater snail Stagnicola elodes (Basommatophora: Lymnaeidae)
Authors: Rudolph Paul H. , Burch J. B.
Published: September 2009

The inheritance of alleles at ten enzyme loci of Stagnicola elodes (Lymnaeidae) was analysed by laboratory crosses. Alleles for alanine aminopeptidase (2 alleles), leucine aminopeptidase (2 alleles), aspartate aminotransferase (2 alleles), β-hydroxybutyrate dehydrogenase-1 (4 alleles), 6-phosphogluconate dehydrogenase (2 alleles), esterase-2 (2 alleles), esterase-3 (2 alleles), esterase-7 (2 alleles), esterase-13 (2 alleles) and esterase-18 (2 alleles) segregate in the F2 generation according to Mendelian expectations. Contingency X2 tests for linkage done on F2 progeny from crosses between strains homozygous for alternate alleles at two loci showed that β-hydroxybutyrate dehydrogenase-1, esterase-13 and esterase-18 are presumably linked.
A gene location for the inheritance of the Cataract Fraser (CatFr) mouse congenital cataract
Authors: Muggleton-Harris A. L. , Festing M. F. W. , Hall M.
Published: September 2009

Animal models which emulate defects similar to those in man are required for medical research. Many investigations on the cellular, developmental and molecular aspects of cataractogenesis use the cataract Fraser (CatFr) mouse. This report shows that the CatFT and Lop lens abnormalities are linked, and are probably allelic genes on chromosome 10. It also shows that the CatFT gene is maintained on an inbred genetic background which differs from 79 other strains; it is proposed that this strain be named CAT.
Dominance is not necessary for heterosis: a two-locus model
Authors: Minvielle Francis
Published: September 2009

Under a two-locus model with additive genes which combine multiplicatively to determine a quantitative trait, heterosis is generally observed in the F1 It is positive only if both frequencies of the best allele at each locus are not higher in the same parental population. In the F2, heterosis depends on the rate of recombination between the two loci. If linkage is tight, F1 superiority is nearly halved in the F2. But if the two genes are independent, heterosis is maintained in the F2 at the same level as in the F1.
Quantitative genetic variability maintained by mutation-stabilizing selection balance in finite populations
Authors: Keightley Peter D. , Hill William G.
Published: September 2009

Models of variability in quantitative traits maintained by a balance between mutation and stabilizing selection are investigated. The effects of mutant alleles are assumed to be additive and to be randomly sampled from a stationary distribution. With a two-allele model the equilibrium genetic variance in an infinite population is independent of the distribution of mutant effects, and dependent only on the total number of mutants appearing per generation. In a finite population, however, both the shape and standard deviation of the distribution of mutant effects are important. The equilibrium variance is lower when most of the mutational variance is contributed by few genes of large effect. Genes of small effect can eventually contribute substantially to the variance with increasing population size (N.) The equilibrium variance can be higher in a finite than an infinite population since near-neutral alleles can drift to intermediate frequencies where selection is weakest. Linkage leads to a reduction in the maintained variance which is small unless linkage is very tight and selection is strong, but the reduction becomes greater with increasingNsince more mutants segregate. A multi-allele model is simulated and it is concluded that the two-allele model gives a good approximation of its behaviour. It is argued that the total number of loci capable of influencing most quantitative traits is large, and that the distribution of mutant effects is highly leptokurtic with the effects of most mutants very small, and such mutants are important in contributing to the maintained variance since selection against them is slight. The weakness of the simple optimum model is discussed in relation to the likely consequences of pleiotropy.
Genomic organization inCaenorhabditis elegans: deficiency mapping on linkage group V(left)
Authors: Rosenbluth Raja E. , Rogalski Teresa M. , Johnsen Robert C. , Addison Linda M. , Baillie David L.
Published: September 2009

In this study we genetically analyse a large autosomal region (23 map units) inCaenorhabditis elegans.The region comprises the left half of linkage group V [LGV(left)] and is recombinationally balanced by the translocationeT1(III; V). We have used rearrangement breakpoints to subdivide the region from the left end of LGV todaf-11into a set of 23 major zones. Twenty of these zones are balanced byeT1.To establish the zones we examined a total of 110 recessive lethal mutations derived from a variety of screening protocols. The mutations identified 12 deficiencies, 1 duplication, as well as 98 mutations that fell into 59 complementation groups, significantly increasing the number of available genetic sites on LGV. Twenty-six of the latter had more than 1 mutant allele. Significant differences were observed among the alleles of only 6 genes, 3 of which have at least one ‘visible’ allele. Several deficiencies and 3 alleles oflet-336were demonstrated to affect recombination. The duplication identified in this study issDp30(V;X). Lethal mutations covered bysDp30were not suppressed uniformly in hermaphrodites. The basis for this non-uniformity may be related to the mechanism ofXchromosome dosage compensation inC. elegans.
Phenotypic characterization and genetic analysis of twenty dominant cataract mutations detected in offspring of irradiated male mice
Authors: Kratochvilova Jana , Favor Jack
Published: September 2009

Twenty autosomal dominant cataract mutations were detected among the offspring of male mice irradiated with γ- or X-rays. The single or fractionated doses ranged from 5.34 to 10.2 Gy. The phenotypic manifestation and penetrance of the mutations as well as fertility and viability of the mutants were studied by extensive breeding. Manifestation of 4 mutations was limited to the lens. Sixteen mutations were characterized by multiple ocular anomalies, of which 4 mutations also affected other organs of the body. Seventy per cent of the mutations caused severe opacity of the lens or lens and cornea. Homologous hereditary diseases in man would be juvenile cataracts with serious impairment of vision or blindness. Expressivity of the lens opacities was almost constant whereas the accompanied defects varied with respect to their severity in different individuals as well as in eyes of an individual. Phenotypic differences dependent on the genetic background could not be observed. Fourteen mutations were classified as mutations with complete penetrance without any effect on viability and fertility of heterozygotes. Four other mutations were shown to be fully penetrant but the viability of the heterozygotes was impaired. Two mutations had incomplete penetrance with no viability or fertility effects. Of the 14 mutations with complete penetrance and normal viability and fertility 6 were shown to be homozygous viable, 1 semi-lethal and 7 lethal.
Age-related reactivation of an X-linked gene close to the inactivation centre in the mouse
Authors: Brown Sheila , Rastan Sohaila
Published: September 2009

Age-related reactivation of an X-linked gene which maps close toXce, the X chromosome inactivation centre, has been observed. In five female mice which carried the X-linked coat colour geneMobloon the reciprocal translocation T(X;16)16H (Searle's translocation), and the wild-type gene on the normal X chromosome, and therefore expressed theMoblophenotype due to the non-random inactivation characteristic of Searle's translocation, progressive darkening of the coat was observed as the animals aged. This is due to reactivation of the previously inactivated wild-type gene at theMolocus on the normal X chromosome. As theMolocus is located 4 cM distal toXce, the X chromosome inactivation centre, these observations provide evidence of age-related instability of inactivation of an X-linked gene close to the inactivation centre.
A transposable genetic element associated with positive regulation of G6PD gene expression inDrosophila melanogaster
Authors: Itoh Masanobu , Iwabuchi Mari , Yorimoto Naoki , Hori Samuel H.
Published: September 2009

The DNA structures around the G6PD coding region in three high-G6PD activity mutants and their low-activity revertants ofDrosophila melanogasterwere analysed by Southern blot using a cloned G6PD gene as a probe. As a result, two kinds of insertion sequences were found; one was present just 5′ to exon I (Ins1), and the other within the intron (Ins2). The Ins1 sequence was 3·5 Kb in two mutants and 2·9 Kb in one mutant. In both cases, it consisted of a core sequence either 1·2 or 0·6 Kb long flanked by terminal repeats. On the other hand, low-activity revertants possessed either a defective Ins1 or no Ins1. The Ins2 sequence was found in all mutants and revertants, but not in Canton S. Although a recombinant phage carrying the DNA fragment spanning the entire Ins1 has not been obtained, sequencing data of the clone containing only the terminal repeats demonstrated that the repeats are defective P elements. Comparison of the genomic DNA structures of mutants and revertants suggested that the element responsible for the positive regulation of the G6PD gene in the mutants would probably be the core sequence, but not the flanking defective P elements. It was also conjectured that the 1·2 Kb core sequence might be composed of two identical elements, which might transpose independently.
The epistasis ofAdhandGpdhallozymes and variation in the ethanol tolerance ofDrosophila melanogasterlarvae
Authors: McKechnie Stephen W. , Geer Billy W.
Published: September 2009

The role of epistatic interaction of allozymes in the determination of variation in larval ethanol tolerance ofDrosophila melanogasterwas examined. Isofemale lines from the Tahbilk Winery were made homozygous for different common alleles of alcohol dehydrogenase (Adh) and sn-glycerol-3-phosphate dehydrogenase (Gpdh). When fed 6% ethanol, all the lines had reduced survival and, in the survivors, reduced body weight and lengthened development time. A strong positive correlation between tolerance and development time suggested that alleles responsible for slowing development on ethanol also increased ethanol tolerance. Analysis of larval ethanol tolerance over four generations showed that larvae of theAdhffGpdhff, andAdhssGpdhssallelic combinations were more tolerant than larvae with the other combinations. However, these genotypes were not associated with the slowing of development nor the weight loss on ethanol. Hence, larvae with certain combinations ofAdhandGpdhallozymes may have a greater capacity to metabolize ethanol and be more tolerant to its toxic effects.
A steep cline for mitochondrial DNA in Danish mice
Authors: Vanlerberghe F. , Boursot P. , Nielsen J. T. , Bonhomme F.
Published: September 2009

One hundred and ninety-eight mice trapped along a south–north transect through the Danish hybrid zone betweenMus musculus domesticusandM. m. musculuswere typed for mitochondrial DNA (mtDNA), theYchromosome and ten autosomal loci encoding diagnostic proteins. The southern (domesticus) populations display two mtDNA variants (S1 and S2) and the northern (musculus) have a third mtDNA variant (N) ofdomesticusorigin. Across the hybrid zone defined by ten autosomal loci, there is a steep dine between the southern and northern types of mtDNA. As well as confirming an earlier finding that Danishmusculusall have adomesticusmtDNA (Ferriset al.1983a, &b), our results show that this mtDNA takeover is not the result of a persistent mitochondrial gene flow between the two subspecies. While the coincident dines for the ten autosomal loci and the abrupt dine for theYchromosome can be explained by selection, it is less likely to be the case for the mtDNA exchanges. We discuss the possible role of sex-linked migration and genetic drift to account for the distribution of the mitochondrial variants.
The localization ofG6pd, glucose-6-phosphate dehydrogenase, andmdx, muscular dystrophy in the mouseXchromosome
Authors: Peters J. , Ball S. T. , Charles D. J. , Pretsch W. , Bulfield Grahame , Miller D. , Chapman V. M.
Published: September 2009

A low activity mutant of glucose-6-phosphate dehydrogenase,G6pda-m1Neuhas been used to positionG6pdin the mouseXchromosome. Linkage tests withtabby,Taandharlequin,Hq, indicate a likely gene order ofHq–G6pd–Ta. Muscular dystrophy,mdx, has been located by two-and three-point crosses usingHprt,Pgk-1andMobloand suggest a gene order ofHprt–mdx–Pgk-1–Moblo. Together with existing linkage data a tentative order for the seven loci isHq–Hprt–G6pd–mdx–Ta–Pgk-1–Moblo. The relative positions ofG6pdandmdxhave not been directly tested andG6pdis assigned provisionally proximal tomdx. In the three point test usingHq,G6pdandTathe recombination frequency found betweenHqandTawas 9·9 ± 2·6%, substantially less than the value of 20·5 ± 2·1% reported by Isaacsonet al.(1974).
Insertion-deletion variation at theyellow-achaete-scuteregion in two natural populations ofDrosophila melanogaster
Authors: Beech Robin N. , Brown Andrew J. Leigh
Published: September 2009

We have surveyed the region of theXchromosome ofDrosophila melanogasterwhich encodes theyellow, achaeteandscutegenes for restriction map variation. Two natural populations, one from North Carolina, U.S.A. and the other from southern Spain were screened for variation at about 70 restriction sites and for variation due to DNA insertion or deletion events in 120 kilobases of DNA. Mean heterozygosity per nucleotide was estimated to be 0·0024 and 15 large insertions were found in the 49 chromosomes screened. Extensive disequilibrium between polymorphic sites was found across much of the region in the North Carolina population. The frequency of large insertions, which usually correspond to transposable genetic elements, is significantly lower than has been observed in autosomal regions of the genome. This is predicted forX-linked loci by certain models of transposable element evolution, where copy number is restricted by virtue of the recessive deleterious effects of the insertions. Our results appear to support such models. The deficiency of insertions may in this case be enhanced by hitch-hiking effects arising from the high level of disequilibrium.
Thein vivoandin vitrotransmission frequencies of thetw5-haplotype in mice
Authors: Garside William , Hillman Nina
Published: September 2009

The recessivetω5-haplotype, a complete haplotype, is transmitted by heterozygous male mice at very high frequencies (> 0·90) in normal matings. The present studies were undertaken to determine the effects of delayed matings andin vitrofertilizations on this phenotypic expression. Males carrying thetω5-haplotype ( + /tω5) were first tested for their frequencies of transmission of the mutant 17th chromosome in both normal and delayed matings. Spermatozoa obtained from these same males were then used to fertilize eggsin vitro.Thein vivoandin vitrotransmission frequencies were found to be statistically equivalent in all types of inseminations. Anin vitrofertilization time course study showed that the same percentages of eggs are fertilized bytω5- bearing spermatozoa when the gametes are coincubated for either 2 or 6 h. The data lead to the conclusion that the transmission frequency of thetω5-haplotype is not affected either by the length of time elapsing between insemination and fertilization or by the environment in which fertilization occurs.
The mutational load of a multigene family with uniform members
Authors: Ohta Tomoko
Published: September 2009

The mutational load of a multigene family with uniform members was studied by computer simulations. Two models of selection, truncation and exponential fitness, were examined, by using a simple model of gene conversion. It was found that the load is much smaller than the Haldane–Muller prediction under the truncation selection, and that it becomes approximately equal to the value calculated by the formula,nv(1 −q)/(m−nq), wherenis the copy number,vis the rate of detrimental mutation per gene copy,mis the truncation point in terms of the number of detrimental genes eliminated, andqis the equilibrium frequency of detrimental mutation. However the equilibrium frequency cannot be analytically obtained. For the exponential fitness model, the load is close to the Haldane–Muller value. When there is no gene conversion, the load becomes larger than the cases with conversion both for the truncation and the exponential fitness models. Thus, gene conversion or other mechanisms that are responsible for contraction–expansion of mutants on chromosomes helps eliminating deleterious mutations occurring in multigene families.
Mutant alleles of the meiotic locus,mei-9, differ in degree of effects on rod chromosome magnification and ring chromosome transmission inDrosophila
Authors: Komma Donald J. , Graves Heath , Endow Sharyn A.
Published: September 2009

Two mutant alleles of the meiotic locus,mei-9, have been examined for their effect on magnification of a rodXbbchromosome and transmission of a ringXbbchromosome under magnifying conditions. Our results indicate that the effects of these two mutations are allele-specific:mei-9astrongly inhibits both rod chromosome magnification and ring chromosome loss under magnifying conditions, whilemei-9bhas a smaller inhibitory effect on rod chromosome magnification and on the transmission of ring chromosomes under magnifying conditions. These observations can be explained by a difference in leakiness between the two alleles. Our results demonstrate that mutants defective in excision repair and repair replication inhibit ribosomal gene magnification. This suggests that a component of the excision repair pathway is involved in the process of magnification.
Responses to divergent selection for plasma concentrations of insulin-like growth factor-1 in mice
Authors: Blair H. T. , McCutcheon S. N. , Mackenzie D. D. S. , Gluckman P. D. , Ormsby J. E. , Brier B. H.
Published: September 2009

A divergent selection experiment with mice, using plasma concentrations of insulin-like growth factor-1 (IGF-1) at 42 days of age as the selection criterion, was undertaken for 7 generations. Lines were not replicated. To obtain sufficient plasma for the IGF-1 assay, blood from four individuals was volumetrically bulked to obtain a litter mean IGF-1 concentration. This necessitated the use of between family selection. Although inbreeding accumulated in a linear fashion in each of the high, control and low lines, the rates were different for each line (3·6, 1·6 and 5·3% per generation for the high, control and low lines, respectively). As a consequence, the effects of selection and inbreeding are confounded in this experiment. Divergence between the high and low lines in plasma concentrations of IGF-1 continued steadily until generation 5. In generations 6 and 7, there was a reduced degree of divergence and this contributed towards the low realized heritability value of 0.15 ± 0.12. Six-week liveweight showed a steady positive correlated response to selection for or against plasma concentrations of IGF-1 until generation 4 (high-low difference = 1·7 g = 12%). In generation 5, a substantial drop in 6-week liveweight in the low line relative to both the high and control lines occurred (high-low difference, 3·9; g, 25%). This difference was maintained until generation 7.

This experiment suggests that genetic variation exists at 6 weeks of age in plasma concentrations of IGF-1 in mice. Furthermore, genetic covariation between plasma IGF-1 concentrations and liveweight at 6 weeks of age is likely to be positive. Further experiments have been initiated to examine these theories.
A genetic model of interpopulation variation and covariation of quantitative characters
Authors: Zeng Zhao-Bang
Published: September 2009

Evolutionary consequences of natural selection, migration, genotype–environment interaction, and random genetic drift on interpopulation variation and covariation of quantitative characters are analysed in terms of a selection model that partitions natural selection into directional and stabilizing components. Without migration, interpopulation variation and covariation depend mainly on the pattern and intensities of selection among populations and the harmonic mean of effective population sizes. Both transient and equilibrium covariance structures are formulated with suitable approximations. Migration reduces the differentiation among populations, but its effect is less with genotype–environment interaction. In some special cases of genotype–environment interaction, the equilibrium interpopulation variation and covariation is independent of migration.
Isolation ofBacillus subtilistransformation-deficient mutants and mapping of competence genes
Authors: Mastromei Giorgio , Barberio Claudia , Pistolesi Stefania , Polsinelli Mario
Published: September 2009

We have isolated and characterized 48Bacillus subtiliscompetence-deficient mutants. The mutants, obtained by nitrososoguanidine mutagenesis or by insertional mutagenesis with transposon Tn917, had a reduced transformation frequency and a wild-type transduction frequency. Thecommutations were mapped by PBS1 transduction and at least four newcomgenes have been identified. The mutants were also characterized for their capacity to bind and take up the transforming DNA.
Differences in allele frequencies ofAatbetween high- and mid-rocky shore populations ofLittorina saxatilis(Olivi) suggest selection in this enzyme locus
Authors: Johannesson Kerstin , Johannesson Bo
Published: September 2009

Samples of the intertidal prosobranchLittorina saxatiliswere collected along vertical transects from high- to mid-store levels at five different geographic locations of western Europe. Electrophoretic screening of ten metabolic enzymes revealed five highly polymorphic loci. Four of these showed no or few significant differences in allele frequencies between high- and mid-shore samples ofLittorina saxatilis. The fifth locus,Aat(aspartate aminotransferase, EC 2.6.1.1), showed clinal variation in allele frequencies over the few metres of each transect, suggesting that this locus, or a coupled locus, is under selection with a slow allele (Aat100) favoured in mid-shore habitats and a faster allele (Aat120) selected for in the high littoral fringe.
Comparison of the regulation of P elements in M and M′ strains ofDrosophila melanogaster
Authors: Ronsseray Stéphane , Lehmann Monique , Periquet Georges
Published: September 2009

M and M′ strains ofDrosophila melanogasterin the P-M system of hybrid dysgenesis were compared in two series of tests, with the following results. (1) Thesinged-weakhypermutability regulation test showed that M′ strains had lower P excision rates than M strains, suggesting that P-elements repression must occur in M′ strains although it is not detectable by gonadal dysgenesis assays. (2) The evolution of mixed P + M and mixed P + M′ populations was compared, using a strong P strain. The P + M cultures invariably evolved in a few generations into strong P cultures, while the P + M′ cultures evolved into P-type cultures with reduced P-factor potentials. However, after 30 generations of culture, both these types of mixed cultures had similar P copy numbers, suggesting that regulation of copy number had occurred in them.
Non-additive inheritance of glucose phosphate isomerase activity in mice heterozygous at theGpi-1sstructural locus
Authors: West John D. , Flockhart Jean H.
Published: September 2009

The activity of blood glucose phosphate isomerase (GPI-1) in mice heterozygous for various alleles at theGpi-1sstructural locus (heterozygotesa/b, a/candb/c) was significantly higher than expected, on the basis of additive inheritance, from the levels in parental homozygotes. Moreover, the GPI-1 activity was higher ina/bheterozygotes than in either parent (heterosis). Studies of heat stability with kidney homogenates revealed that the relative stabilities of GPI-1 dimers was AA > AB > BB > AC ≥ BC > CC. Differences in dimer stabilitiesin vivowould affect the total GPI-1 levels in heterozygotes and could account for non-additive inheritance but would be insufficient to explain heterosis for GPI-1 activity. Other possible contributing factors include unequal production or stability of monomers, or higher catalytic activity of heterodimers. Monomers could also associate non-randomly but this would not be sufficient to explain heterosis. It is clear that non-additive inheritance patterns may be produced by variants of either structural or regulatory genes.