bluuebunny/crossref_metadata_2025 huggingface dataset:
Fitness patterns and phenotypic plasticity in a spatially heterogeneous environment
Authors: Zhivotovsky Lev A. , Feldman Marcus W. , Bergman Aviv
Published: September 2009

We analyse patterns of the means and variances of genotypic fitnesses across different niches in a randomly mating haploid population. The population inhabits a spatially heterogeneous environment where it is subject to mutation and weak multilocus additive selection, with different selection coefficients in different niches. Approximate analytical expressions are derived for the stationary mean and variance of genotypic fitnesses among the niches in terms of environmental and genetic parameters. As a special case, we analyse an environment described by a variablet, distributed among the niches with meant*and variance D*, and quadratic decrease in correlation between environments as a function of the difference in values oft. If the niches have the same qualities, the mean and variance of genotypic fitnesses evolve to be quadratic functions oftthat achieve their maximum and minimum, respectively, att*. With unequal niche qualities, these are non-polynomial functions that attain their extrema at different, usually intermediate values oft, although the coefficient of variation of the genotypic fitnesses still attains its minimum neart*. The functions involve the total mutation rate, the contribution of the loci to genotypic fitnesses, and the frequency and quality distributions of the niches. Thus, for this relatively simple model the norms of reaction may be calculated in terms of the detailed properties of the environmental heterogeneity, and the genetic system.
Two independent cis-acting elements regulate the sex- and tissue-specific expression ofyp3inDrosophila melanogaster
Authors: Ronaldson Elaine , Bownes Mary
Published: September 2009

InDrosophila, the threeyolk protein(yp) genes are transcribed in a sex-, tissue- and developmentally specific manner, providing an ideal system in which to investigate the factors involved in their regulation. The yolk proteins are synthesized in the fat body of adult females, and in the ovarian follicle cells surrounding the developing oocyte during stages 8–10 of oogenesis. We report here an analysis of theyolk protein 3(yp3) gene and its flanking sequences by means of P-element mediated germ-line transformation and demonstrate that a 747 bp promoter region is sufficient to direct sex-specific expression in the female fat body and both the temporal- and cell-type-specificity of expression during oogenesis. Two elements that independently governyp3transcription in these tissues have been separated and no other sequences in the upstream, downstream or coding regions have been identified that are autonomously involved inyp3expression.
Rates of change of genetic parameters of body weight in selected mouse lines
Authors: Heath S. C. , Bulfield G. , Thompson R. , Keightley P. D.
Published: September 2009

A method based on the animal model is described which allows the estimation of continuous changes in variance components over time using restricted maximum likelihood (REML). The method was applied to the analysis of a selection experiment in which a foundation population formed from a cross between two inbred strains of mice (C57BL/6J and DBA/2J) was divergently selected for 6 week body weight over 20 generations. The analysis suggested that there was an increase in phenotypic variance of about 50% in the low selected lines over the course of the experiment which was attributed to increases in the environmental and additive variance components. Variance changes in the High selected lines were generally smaller than in the Low lines, although there was an estimated 20% increase in the environmental variance. Simple models to explain these effects involving dominance, linkage and epistasis were explored. Testing which of these was responsible for the variance changes noted in this experiment (if any) is difficult, although the epistasis and dominance models require less stringent conditions than the linkage model, and the dominance model is supported by evidence of heterosis in the F1.
Pattern and frequency of nocodazole induced meiotic nondisjunction in oocytes of mice carrying the ‘tobacco mouse’ metacentric Rb(16.17)7Bnr
Authors: Everett C. A. , Searle J. B.
Published: September 2009

Oocytes from (C3H/HeH × 101/H)F1and Rb(16.17)7Bnr homozygous females were exposed to a range of doses of nocodazolein vitro. The spindle poison caused a dose dependent increase in metaphase I (MI) arrest and hyperploidy. A concentration of 0·03 μg/ml was found to induce a maximum hyperploid frequency of 3·1% and 11·6% respectively without a high level of MI arrest. Between 0·03 and 0·05 μg/ml MI arrest increased substantially and reached a frequency of approximately 90%. In a further experiment oocytes from Rb7 homozygous, heterozygous and 3H1 females were exposed to 0·03 μg/ml nocodazole 4, 6 or 8 h after the onset of maturation. The phase at which the spindle was inhibited resulted in a specific pattern of nondisjunction which in turn was dependent on whether the female carried an Rb metacentric. 3H1 oocytes gave a normally distributed pattern of increase in aneuploid frequency (over the spontaneous value) centering around a 6 h application. This was thought to be due to the interaction of chromosomes with the microtubules of the spindle during attachment and/or alignment. In contrast both Rb homozygotes and heterozygotes gave the same biphasic response, with a high frequency of aneuploidy in the oocytes when nocodazole was applied 4 and 8 h after the onset of maturation. In Rb homozygotes we demonstrated that the Rb bivalent underwent nondisjunction more frequently than the average acrocentric, when nocodazole was administered early. It can be assumed that the Rb trivalent in Rb heterozygotes showed a similar response. This early Rb specific effect, in combination with a delayed-version of the acrocentric effect found in the 3H1 mice was thought to generate the biphasic pattern. We discuss the implications of (a) the different meiotic behaviours of metacentrics and acrocentrics and (b) the meiotic delay in Rb mice.
Marker assisted selection for genetic improvement of animal populations when a single QTL is marked
Authors: Ruane J. , Colleau J. J.
Published: September 2009

A Monte Carlo simulation study to evaluate the benefits of marker assisted selection (MAS) in small populations with one marked bi-allelic quantitative trait locus (QTL) is described. In the base generation, linkage phase equilibrium between the markers, QTL and polygenes was assumed and frequencies of 0·5 for the two QTL alleles were used. Six discrete generations of selection for a single character measured on both sexes followed. An additive genetic model was used with the QTL positioned midway between two highly polymorphic markers. Schemes were simulated with a distance of 10 cM between the QTL and either of the two markers and with the QTL explaining 1/8 of the total genetic variance in the base generation. Values of 0·5, 0·25 or 0·1 were assumed for the heritability. Eight males and 16, 32 or 64 females were selected each generation with each dam producing four sons and four daughters as candidates for the next generation. Animals were evaluated with a conventional BLUP animal model or with a model using marker information. MAS resulted in substantially higher QTL responses (4–54%), especially with low heritabilities, than conventional BLUP but lower polygenic responses (up to 4%) so that the overall effect on the total genetic response, although in the majority of cases favourable, was relatively small. With QTLs of larger size (explaining 25% of the genetic variance) comparable results were found. When the distance between the QTL and the markers was reduced to 2 cM, genetic responses were increased very slightly with a heritability of 0·5 whereas with a heritability of 0·1 responses were increased by up to 10%, compared with conventional BLUP. Results emphasize that MAS should be most useful for lowly heritable traits and that once QTLs for such traits have been identified the search for closely linked polymorphic markers should be intensified.
Commensalism, adaptation and gene flow: mosquitoes of theCulex pipienscomplex in different habitats
Authors: Chevillon Christine , Eritja Roger , Pasteur Nicole , Raymond Michel
Published: September 2009

Two ecotypes have been described forCulex pipiensmosquitoes of the temperate zone: a human commensal type and a feral type, but their degree of evolutionary differentiation and taxonomic status are still unclear. The commensal form is characterized by life-history traits probably adaptive to underground man-made environments. This situation has sometimes been considered as an example of recent speciation although the existence of intermediate forms indicates that the balance between gene flow and disruptive selection should first be assessed. The present study was concerned with (1) the determination of biological traits involved in adaptation to commensalism, and (2) the pattern of gene flow within and between ecotypes in a restricted area. It was found that (1) significant differences in biological traits exist between mosquitoes from different habitats, (2) characteristics of the commensal type are not universal in mosquitoes from underground man-made habitats, (3) allozyme markers do not clearly differentiate ecotypes and (4) insecticide resistance genes, which reveal recent migration, occur in each ecotype. These results are discussed in the context of possible speciation due to commensalism.
The distribution of transposable elements on X chromosomes from a natural population ofDrosophila simulans
Authors: Nuzhdin Sergey V.
Published: September 2009

The distribution of 13 transposable element families along 15 X chromosomes from an African natural population ofDrosophila simulanswas determined byin situhybridization to polytene chromosomes. The transposable elements cloned fromDrosophila melanogasterall hybridized withDrosophila simulanschromosomes. The number of copies per family was 3·5 times lower in the latter species and correlated with the copy number per family inDrosophila melanogaster. With the exception of297, the copy number per chromosome followed a Poisson distribution. Element frequencies per chromosome band were generally low. However, several sites of the distal region and the base of the X chromosome had high frequencies of occupation. Elements had higher abundance at the base of the chromosome compared to distal regions. Overall, the distribution of transposable elements inDrosophila simulansis similar to that found inDrosophila melanogaster. These data provide evidence for the operation of a force (or forces) opposing transpositional increase in copy number, and that this force is weaker at the bases of chromosomes, consistent with the idea that recombination between elements at non-homologous sites contains TE copy number. The reduction in copy number of all TE families inDrosophila simulanscompared toDrosophila melanogastercan be explained by stronger selection against transposable element multiplication and/or lower rates of transposition inDrosophila simulans.
The genetics of tasting in mice VII. Glycine revisited, and the chromosomal location ofSacandSoa
Authors: Lush I. E. , Hornigold N. , King P. , Stoye J. P.
Published: September 2009

Previous work which appeared to show that some strains of mice taste glycine solutions as bitter has been found to be in error. The bitterness came from copper glycinate which formed in the brass drinking spouts. Taste testing with copper glycinate shows that the genetical data identifying the geneGlbare still valid. The close linkage ofGlbandRuahas been confirmed. Most strains of mice prefer glycine solution to water, presumably because the glycine tastes sweet. The degree of preference for glycine is correlated with the degree of preference for other sweet substances such as saccharin or acesulfame. The genedpaappears not to be involved.

The sweetness tasting geneSachas been mapped to chromosome 4 at 8·1 ± 3·4 cM distal toNppa(formerlyPnd). The bitterness tasting geneSoais very closely linked toPrpon chromosome 6 (no recombinants among 67 backcross progeny). It is suggested that the sweetness and bitterness tasting genes have descended from a common ancestral tasting gene which existed before the tetraploidization of the genome which took place in early vertebrate evolution.
The cellular basis for interaction of sterility factors in the mousethaplotype
Authors: Johnson Linda R. , Pilder Stephen H. , Olds-Clarke Patricia
Published: September 2009

Thethaplotypes are variant forms of the proximal one-third of chromosome 17 in the mouse. They contain four inversions (relative to the wildtype DNA) extending over most of this region and house a number of male sterility factors. Males carrying two completethaplotypes (t/t) are sterile, as are males homozygous forS2, the sterility factor located in the most distal (relative to the centromere) inversion. Males homozygous for the sterility factorS1, located in the most proximal inversion, are not sterile; however, if such a male also is heterozygous for other sterility factors, then sterility results. It has been suggested therefore that homozygosity forS1enhances the detrimental action of other sterility factors. Sperm fromt/tmales have severe motility defects and are unable to penetrate investment-free eggs, while sperm from fertilet/+ mice have less serious motility defects and exhibit a delay in penetration of investment-free eggs. To determine whether homozygosity forS1enhances the cellular defects exhibited by sperm from mice heterozygous for other sterility factors, we compared the motility and egg-penetrating ability of sperm from fertile mice homozygous forS1to that of sperm from mice carrying one completethaplotype and one proximal or distal partialthaplotype. The data suggest that sperm from males carrying a proximal partialthaplotype and a completethaplotype have serious defects in motility and penetration of the investment-free egg, and support the hypothesis thatS1enhances the detrimental effects of other sterility factors within thethaplotype.
Induction of unstable alleles at the temperature-sensitiveVirescent-1gene of maize using the transposable elementDissociation
Authors: Cerioli Sergio , Ballarini Stefania , Uhrig Helmut , Scalzotto Eugenio , Marocco Adriano
Published: September 2009

Transpositive mutagenesis was employed to prepare genetic strains useful in cloning theVirescent-1locus (V1) of maize. A stepwise approach was used based on: (1) the isolation of putative insertion phenotypes (62 cases); (2) the verification of the genetic nature of the selected events (36v1-mmutant alleles induced); (3) the accurate genetic study of 11 alleles; (4) the genetic assessment that the allelesv1-m1andv1-m4are due to the insertion ofa Dselement into the locusV1; (5) the proof that aDs-like DNA element induces the inactivation of the wild type function in the allelev1-m1. The phenotype of the unstable alleles, studied by germinating and keeping maize seedlings at the temperature of 18 °C, are the following: allelesv1-m1, v1-m9, v1-m11, v1-m17andv1-m18showing a few revertant green sectors on their leaves;v1-m4exhibiting a reverse type of variegation; allelesv1-m2andv1-m13with a coarse pattern of variegation; allelesv1-m12, v1-m21andv1-m23frequently showing leaves part green with white stripes and part white with green stripes. For the alleles studied, in addition to somatic instability, germinal reversions also occurred. In some cases, these reversions resulted in stable derivatives with a different colour from that of the wild-type (‘near green’ or pale phenotypes). The results presented not only allow thev1-m1allele to be chosen as a starting material for cloning theV1locus, but also define the molecular strategy to be followed.
Response to selection from new mutation and effective size of partially inbred populations. I. Theoretical results
Authors: Caballero Armando , Santiago Enrique
Published: September 2009

The effects of partial inbreeding on effective population size and rates of fixation of mutant genes are investigated in selected populations. Truncation selection and an infinitesimal model of gene effects for the selected trait are assumed. Predictions of effective size under this model are given for partial selfing and partial full-sib mating and an extension to a more general model is outlined. The joint effect of selection and partial inbreeding causes a large reduction in the effective size relative to the case of random mating. This effect is especially remarkable for small amounts of selected genetic variation. For example, for initial heritability 0·1 and proportion selected 1/6, the ratio of effective size to population size is 0·10 in populations with about 90% selfing while it is 0·85 in random mating populations. The consequence is a reduction in the fixation probability of favourable genes and, therefore, a reduction in the final response to selection. Stochastic simulations are used to investigate the effects of partial inbreeding and selection on fixation and extinction rates of genes of large effect and of recessive lethals with effects on the selected trait. For genes of very large effect, the effective size is not a critical factor and it is expected that partial inbreeding will be efficient in increasing fixation rates of recessive mutants. Lethal recessives are eliminated more frequently and their equilibrium frequency is lower under partial inbreeding, but only when their effects on the heterozygote are not very large.
The constraints of finite size in asexual populations and the rate of the ratchet
Authors: Gessler Damian D. G.
Published: September 2009

An analysis of mutation accumulation in finite, asexual populations shows that by modeling discrete individuals, a necessary condition for mutation–selection balance is often not met. It is found that over a wide parameter range (wheneverN e−μ/s< 1, whereNis the population size, μ is the genome-wide mutation rate, andsis the realized strength of selection), asexual populations will fail to achieve mutation–selection balance. This is specifically because the steady-state strength of selection on the best individuals is too weak to counter mutation pressure. The discrete nature of individuals means that if the equilibrium level of mutation and selection is such that less than one individual is expected in a class, then equilibration towards this level acts to remove the class. When applied to the classes with the fewest mutations, this drives mutation accumulation. This drive is in addition to the well-known identification of the stochastic loss of the best class as a mechanism for Muller's ratchet. Quantification of this process explains why the distribution of the number of mutations per individual can be markedly hypodispersed compared to the Poisson expectation. The actual distribution, when corrected for stochasticity between the best class and the mean, is akin to a shifted negative binomial. The parameterization of the distribution allows for an approximation for the rate of Muller's ratchet whenN e−μ/s< 1. The analysis is extended to the case of variable selection coefficients where incoming mutations assume a distribution of deleterious effects. Under this condition, asexual populations accumulate mutations faster, yet may be able to survive longer, than previously estimated.
Effect of non-random sampling on the estimation of parameters in population genetics
Authors: Tajima Fumio
Published: September 2009

The amount and pattern of genetic variation in a population can be estimated from genes or DNA sequences sampled from the population. Although random sampling is assumed in almost all cases, we often do not know whether sampling is random or not. Using a simple non-random sampling model, the effects of non-random sampling on the estimation of parameters in population genetics were investigated. This non-random sampling model assumes thatngenes are randomly sampled with replacement frommgenes which were randomly sampled from a large random mating population, and various degrees of non-randomness can be generated by changing the value ofm. The results obtained show that the effect of non-random sampling on the number of alleles and the number of segregating sites is substantially large whereas the effect of non-random sampling on heterozygosity and the average number of nucleotide differences is negligibly small unless non-randomness is extremely large. The effects of non-random sampling on the tests of neutrality were also investigated, and the results obtained indicate that the effect of non-random sampling is stronger on Fu and Li's tests than on Tajima's test.
The effect of continued selection of phenotypic intermediates on gene frequency
Authors: Curnow R. N.
Published: September 2009

The selection of animals or plants for high values of a certain character may favour not only genotypes associated with these high values but also genotypes associated with high variability. Any differences between genotypes in variability may therefore be of considerable importance in plant and livestock improvement programmes as well as in evolution. The effects of various selection procedures on variability have been studied in three recent experiments [Falconer & Robertson (1956) Falconer (1957) and Prout (1962)]. In these experiments one line was continued by selecting, in each generation, parents with values of a particular character near the population mean. Manning (1955, 1956) has described the effects of this kind of selection applied to cotton. Robertson (1956) derived and discussed the theory of such selection procedures when certain simplifying approximations can be made We shall obtain some more general results and show that Robertson was incorrect in saying that the selection procedure would lead to gene fixation even if the heterozygotes are less variable than the homozygotes. The importance of the results is discussed in section 8.
Genetic variation of relative growth rates inNotonecta undulata: I. The relation of femur length to body length
Authors: Misra R. K. , Reeve E. C. R.
Published: September 2009

This paper presents the first part of a further analysis of data collected many years ago by Clark and Hersh on allometric growth inNotonecta undulata, the water boatman. The data consist of measurements of a number of dimensions, taken each instar, on 72 individuals reared separately from egg to adult. These individuals were the progeny of nine wild females, so that a rough estimate can be made of the magnitude of genetic effects by comparing the variances within and between families. The paper examines the allometric relationship between femur length of the three legs and body length.

The statistical problems in this type of analysis are discussed. There are significant deviations from linearity when the six points for femur length are plotted against body length on a double log graph, but these are small compared with the overall linear trend. The growth coefficients (k) are calculated for the three femurs against body length for each individual, and are analysed for differences between femurs, between sexes and between and within families. This analysis shows that there are significant differences between the three femurs in growth coefficient, but the growth gradient, or pattern ofkvalues between the three femurs does not vary significantly from one individual to another. On the other hand, meankfor the three femurs shows significant individual variation and also a significant variation between families. From this it appears that about one third of the phenotypic variance in mean relative growth rate of the femurs is due to genetic effects.
The pattern of mutation of an unstable gene in Delphinium ajacis
Authors: Dawson G. W. P.
Published: September 2009

1. Inheritance of flower colour in Delphinium ajacis is controlled by a locus with three stable alleles: pb (blue) is dominant to pl (lavender), which is dominant to p (pink). An unstable allele, p*, exists in a number of states, distinguished by the pattern of their mutation to pb and p during the development of the sepals.

2. The rate of occurrence of blue sectors and spots in the developing sepals of p*p* plants is twice that in the sepals of p*pl plants. The rate of mutation to pb apparently falls during the development of the sepals and this is probably due to p* mutating also to the stable p allele.

3. The frequency of pb and p gametes from p*p* plants is twice that from p*pl plants.

4. The pb mutants from p* show no evidence of instability; the controlling element has transposed from the locus.

5. Some p mutants from p* are apparently stable; others can reacquire instability, especially during sexual reproduction. The latter are tentatively interpreted as due to transpositions of the controlling element to other sites within the gene.

6. The instability of p* is only shown in the presence of a dominant activator.

7. Evidence is presented of transposition of the controlling element from p* to a locus controlling the colour of the foliage.
Mi-spotted: a mutation in the mouse
Authors: Wolfe H. Glenn , Coleman D. L.
Published: September 2009

Mi-spotted (misp) is a new mutation in the mouse at the microphthalmia (mi) locus. It has no obvious visible effect in either the heterozygote (misp/+) or homozygote (misp/misp) and was discovered by virtue of its interaction with white (miwh). Mice of genotypemiwh/mispare pale yellow with white spots; yellow areas later become ‘sooty’ at the first moult.

Though mice of genotypesa/a;misp/+ anda/a;misp/mispcannot be visibly distinguished from those ofa/a; +/+, the amount of tyrosine-2-C14incorporated in melanin in skins of 5-day-old mice of these genotypes differed. Assays of tyrosine incorporation were extended to include other non-agouti genotypes differing only at the microphthalmia locus. The amount of tyrosine incorporated was greatest in +/+ followed in order bymisp/+,misp/+,misp/misp,miwh/+,miwh/misp, andmiwh/miwh.

Pigment granules were examined in club hairs of these same genotypes for different regions of the hair shaft. Hairs ofmisp/+,misp/misp, andmi/+ could not be distinguished from +/+ either in number, kind or arrangement of granules. Hairs ofmiwh/+ showed reduced cortical and medullary pigment, especially distally, which was even more pronounced in hairs ofmiwh/misp. Medullary granules ofmiwh/mispvaried greatly in size with a few large yellow-brown granules.
Cytological observations on a duck hybrid: Anas clypeata × Anas penelope
Authors: Slizynski B. M.
Published: September 2009

The chromosomes of the two parental forms and those of the hybrid do not show any detectable numerical or large structural differences. The pairing in the hybrid is frequently abnormal in that both free ends (highly charged with stainable substances) of many chromosomes show strong pairing, while midsegments repel each other. This partial failure of paring suggests that in the two parental forms gene mutations rather than chromosomal structural changes are responsible for incipient divergence.

It is suggested that the stainable substance of the chromosomes acts as a carrier mechanism ensuring orderly pairing, segregation and numerical constancy of bivalents in the hybrid where the partner chromosomes have become partly non-homologous.

The distinction between long and short chromosomes is typical for the avian karyotype, its evolutionary significance is discussed.
The effect of dose-rate on the yield of translocations and dominant lethals following spermatogonial irradiation of mice
Authors: Phillips R. J. S. , Searle A. G.
Published: September 2009

1. F1 (CSH♀ × 101♂) male mice were given 1200 r. 60Co Υ-irradiation over welve weeks and mated twelve weeks after the end of irradiation. The incidences of foetal and neonatal lethality and of semi-sterility in their offspring were compared with those in controls.

2. Embryonic survival to 15 days in the irradiated series was 98·2% that of controls, while the incidence of semi-sterility was 0·9% compared with nil in the controls. Neither of these differences is significant.

3. Comparison of these results with the significant rates of induction of dominant lethals and translocations in a previous experiment, in which a dose of 1200 r. acute x-irradiation was given to males of the same hybrid stock, show the existence of a dose-rate effect. Its magnitude cannot at present be accurately estimated.

4. The reasons for this effect are discussed. It is concluded that the main cause of the lowered translocation yield is that restitution of breaks will be favoured at low dose-rates, with less opportunity for the formation of interchanges. This could partly account for the lowered rate of induction of dominant lethals as well, but a full explanation is not yet possible.
Diabetes insipidus associated with oligosyndactyly in the mouse
Authors: Falconer D. S. , Latsyzewski M. , Isaacson J. H.
Published: September 2009

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.
Changing the relative size of the body parts ofDrosophilaby selection
Authors: Robertson Forbes W.
Published: September 2009

1. Mass selection for both high- and low-ratio of wing to thorax length has been carried out on a population ofDrosophila melanogaster. The response to selection was immediate and sustained. When the experiment was stopped after ten generations, the wing area in the two selected lines differed by about 30%. The heritability estimate worked out at 0·56 ± 0·08.

2. Thorax length remained comparatively unchanged during selection nor was there any change in wing shape. There was some evidence of assymetry of response since there was a relatively greater change in favour of smaller rather than larger size.

3. The tibia length of all pairs of legs showed correlated changes so that the lines with larger or smaller wing sizes had also larger and smaller legs.

4. The normal allometric relation between wing and thorax length, associated with variation in body-size, apparently also changed, so that for a given change in thorax length there was a greater or smaller proportional change in wing size in the high- or low-ratio lines.

5. The changes in relative wing size are due to changes in cell number.

6. It is suggested that the genetic changes due to selection act in the early pupal period when the imaginal discs are undergoing differentiation and proliferation to form imaginal hypoderm and appendages.

7. Tests of genetic behaviour failed to show any departure from additivity in crosses which involved the unselected population and the high-ratio line. But highly significant departures existed in the cross to the low-ratio line. Relatively smaller wing size behaves as largely recessive. Stability of the normal wing/thorax ratio involves dominance and probably also epistasis. The genetic properties of the relative size of the appendage are apparently similar to those which characterize body-size as a whole.

8. It is suggested that selection provides a valuable tool for studying the constancy or lability of the growth patterns which determine morphology.
Transfer delay and chromosome withdrawal during conjugation inEscherichia coli
Authors: De Haan P. G. , Gross J. D.
Published: September 2009

Chromosome transfer has been studied in mating pairs formed during a 5-minute interval, under conditions that prevent the formation of new pairs. It has been found that, despite restriction of the period of effective contact formation, there is a considerable spread in the time at which transfer is initiated in the different mating pairs. In some pairs there is a delay of as much as 15 minutes before transfer commences.

The presence of broth in the medium in which transfer takes place leads to a marked reduction in the stability of pairs involving some Hfr strains, but has little or no effect on pairs involving others. The action of broth can be ascribed to the effect of a complete mixture of amino-acids on the metabolic activity of the donor cells.

A segment of chromosome which has penetrated from the Hfr into the F−cell may be subsequently withdrawn. Withdrawal may take place in more than half of the mating pairs, and probably occurs at the time when the donor and recipient cells separate. It is prevented if the chromosome breaks when conjugation is interrupted.
The kinetics of chromosome transfer in Escherichia coli: a mathematical treatment
Authors: Symonds N.
Published: September 2009

A mathematical treatment has been presented of the ideas of de Haan & Gross concerning transfer delay and chromosomal withdrawal during conjugation In Escherichia coli. The calculations involve three parameters: (i) the maximum delay, λ, which can occur between the formation of effective contact in mating pairs and the initiation of chromosomal transfer, (ii) the probability, b, that mating pairs separate with the withdrawal of that segment of the Hfr chromosome which has entered the female cell, and (iii) the probability, c, that mating pairs separate with the breakage of the Hfr chromosome at the point where it enters the female cell, leaving the injected fragment in the female.

A comparison of the theory with the experimental results of de Haan & Gross obtained when chromosomal transfer occurs either in minimal medium or in broth shows good agreement under the following conditions:

(i) the value of λ is the same under both growth conditions,

(ii) the value of b is the same under both growth conditions,

(iii) the value of c is much greater during transfer in broth than it is in minimal medium.
Mutagenic action of nitrous acid onAspergillus nidulans
Authors: Siddiqi O. H.
Published: September 2009

Nitrous acid is shown to be a potent killing and mutagenic agent forAspergillus nidulans. The kinetics of mutation rates induced by nitrous acid are investigated by means of three phenotypically distinguishable suppressors of methionine requirement. The dose-effect curves for two of the suppressors are non-linear. Amongwandymutants produced by nitrous acid there is a high proportion of sectored mutants. Double screening experiments indicate that at least some of the sectored mutations may be due to the presence of more than one genetic strand at the time of treatment. Two of the suppressor genes respond differentially to nitrous acid treatment.
The frequency inNeurosporatetrads of multiple exchanges within short intervals
Authors: Perkins David D.
Published: September 2009

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 ofNeurospora crassashow 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, exceptAspergillus 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.
Insights into X chromosome inactivation from studies of species variation, DNA methylation and replication, and vice versa
Authors: Migeon Barbara R.
Published: September 2009

I am indebted to Mary Lyon as her X-inactivation hypothesis stimulated my mentor, Barton Childs, and in turn, myself, to think about the consequences of X-inactivation in heterozygous females. I often reread her original papers setting forth the single active X hypothesis, and still marvel at the concise and compelling exposition of the hypothesis and the logical predictions which seemed prophetic at my first reading, and have survived the test of time.

My contribution to this Festschrift reviews evidence derived from studies of DNA methylation, species variation and DNA replication that reveals an important role for methylated CpG islands and suggests a role for late DNA replication in propagating X inactivation from one cell to its progeny. These studies also show that X inactivation is a powerful research tool for identifying the factors which program and maintain developmental processes.
The search for the mouse X-chromosome inactivation centre
Authors: Rastan S. , Brown S. D. M.
Published: September 2009

The phenomenon of X-chromosome inactivation in female mammals, whereby one of the two X chromosome present in each cell of the female embryo is inactivated early in development, was first described by Mary Lyon in 1961. Nearly 30 years later, the mechanism of X-chromosome inactivation remains unknown. Strong evidence has accumulated over the years, however, for the involvement of a major switch or inactivation centre on the mouse X chromosome. Identification of the inactivation centre at the molecular level would be an important step in understanding the mechanism of X-inactivation. In this paper we review the evidence for the existence and location of the X-inactivation centre on the mouse X-chromosome, present data on the molecular genetic mapping of this region, and describe ongoing strategies we are using to attempt to identify the inactivation centre at the molecular level.
Illegitimate pairing of the X and Y chromosomes in Sxr mice
Authors: Cattanach B. M. , Rasberry C. , Burtenshaw M. D. , Evans E. P.
Published: September 2009

X/Y male mice carrying the sex reversal factor, Sxr, on their Y chromosomes typically produce 4 classes of progeny (recombinant X/X Sxr ♂♂ and X/Y non-Sxr ♂♂, and non-recombinant X/X ♀♀ and X/Y Sxr ♂♂) in equal frequencies, these deriving from obligatory crossing over between the chromatids of the X and Y during meiosis. Here we show that X/Y males that, exceptionally, carry Sxr on their X chromosome, rather than their Y, produce fewer recombinants than expected. Cytological studies confirmed that X-Y univalence is frequent (58%) at diakinesis as in X/Y Sxr males, but among those cells with X-Y bivalents only 38% showed normal X-Y pseudo-autosomal pairing. The majority of such cells (62%) instead showed an illegitimate pairing between the short arms of the Y and the Sxr region located at the distal end of the X, and this can be understood in terms of the known homology between the testis-determining region of the Y short arm and that of the Sxr region. This pairing was sufficiently tenacious to suggest that crossing over took place between the 2 regions, and misalignment and unequal exchange were suggested by indications of bivalent asymmetry. Metaphase II cells deriving from meiosis I divisions in which the normal X-Y exchange had not occurred were also found. The cytological data are therefore consistent with the breeding results and suggest that normal pseudo-autosomal pairing and crossing over is not a prerequisite for functional germ cell formation. The data support the concept that Y short arm-Sxr pairing and crossing over may be the mechanism responsible for the occurrence of the Sxr variants reported in the literature.
Sex chromosome configurations in pachytene spermatocytes of an XYY mouse
Authors: Tease Charles
Published: September 2009

Karyotypic investigation of a phenotypically normal but sterile male mouse showed the presence of an XYY sex chromosome constitution. The synaptic behaviour of the three sex chromosomes was examined in 65 pachytene cells. The sex chromosomes formed a variety of synaptic configurations: an XYY trivalent (40%); an XY bivalent and Y univalent (38·5%); an X univalent and YY bivalent (13·8%); or X, Y, Y univalence (7·7%). There was considerable variation in the extent of synapsis and some of the associations clearly involved nonhomologous pairing. These observations have been compared with previously published information on chromosome configurations at metaphase I from other XYY males.
Conserved loci on the X chromosome confer phosphate homeostasis in mice and humans
Authors: Scriver Charles R. , Tenenhouse Harriet S.
Published: September 2009

Several genes expressed in kidney and other tissues determine phosphate homeostasis in extracellular fluid. The major form of inherited hypophosphatemia in humans involves an X-linked locus (HPDR, Xp22.31-p21.3). It has two murine homologues (HypandGy) which map to closely-linked but separate loci (crossover value 0·4%–0·8%). Both murine mutations impair Na+-phosphate cotransport in renal brush border membrane; an associated renal disorder of 1, 25-dihydroxyvitamin D3(1, 25(OH)2D) metabolism has been characterized inHypmice. Whereas experiments with culturedHyprenal epithelium indicate that the gene is expressed in kidney, studies showing the development of the mutant renal phenotype in normal mice parabiosed toHypmice implicate a circulating factor; these findings can be reconciled if the humoral factor is of renal origin. The gene dose effect of HPDR,HypandGyon serum phosphorus values is consistently deviant and heterozygotes resemble affected hemizygotes. The deviant effect is also seen on renal phosphate transport; all mutant females(Hyp/HypandHyp/+) have similar phenotypes. On the other hand, there is a normal gene dose effect of HPDR in mineralized tissue; tooth PRATIO (pulp area/tooth area) values for heterozygotes are distributed between those for affected males and normals. The tooth data imply that the X chromosome locus is expressed in both renal and non-renal cells. The polypeptide product of the X chromosome gene(s) is still unknown.
Localization of the properdin factor complement locus Pfc to band A3 on the mouse X chromosome
Authors: Evans E. P. , Burtenshaw M. D. , Laval S. H. , Goundis D. , Reid K. B. M. , Boyd Y.
Published: September 2009

The locus for properdin (properdin factor complement, Pfc), a plasma glycoprotein, has been mapped to band A3 of the mouse X chromosome by in situ hybridization to metaphase spreads containing an X;2 Robertsonian translocation. The X-linkage of the locus has also been confirmed by analysis of Mus musculus x Mus spretus interspecific crosses. The XA3 localization for Pfc places it in the chromosomal segment conserved between man and mouse which is known to contain at least six other homologous loci (Cybb, Otc, Syn-1 Maoa, Araf, Timp).
Hst-3: an X-linked hybrid sterility gene
Authors: Guénet Jean-Louis , Nagamine Claude , Simon-Chazottes Dominique , Montagutelli Xavier , Bonhomme François
Published: September 2009

A gene, Hst-3, responsible for sterility in F1 males from crosses between Mus spretus and laboratory strains of mice such as C57BL/6, has been localized on the distal part of the X chromosome, using both DNA probes and biochemical markers on a panel of Fl(C57BL/6 × SEG) × C57BL/6 backcross males. This gene may be a model for studying mammalian hybrid sterility.
The hairy ears (Eh) mutation is closely associated with a chromosomal rearrangement in mouse chromosome 15
Authors: Davisson Muriel T. , Roderick Thomas H. , Akeson Ellen C. , Hawes Norman L. , Sweet Hope O.
Published: September 2009

The mouse mutation hairy ears (Eh) originated in a neutron irradiation experiment at Oak Ridge National Laboratory. Subsequent linkage studies withEhand other loci on Chr 15 suggested that it is associated with a chromosomal rearrangement that inhibits recombination since it shows tight linkage with several loci occupying the region extending from congenital goiter (cog) distal to caracul (ca). We report here (1) linkage experiments confirming this effect on recombination and (2) meiotic and mitotic cytological studies that confirm the presence of a chromosomal rearrangement. The data are consistent with the hypothesis of a paracentric inversion in the distal half of Chr 15. The effect of the inversion extends over a minimum of 30 cM, taking into account the genetic data and the cytologically determined chromosomal involvement extending to the region of the telomere.
Deletion analysis of male sterility effects oft–haplotypes in the mouse
Authors: Bennett Dorothea , Artzt Karen
Published: September 2009

We present data on the effects of three chromosome 17 deletions on transmission ratio distortion (TRD) and sterility of severalt-haplotypes. All three deletions have similar effects on male TRD: that is,Tdel/tcompletegenotypes all transmit theirt–haplotype in very high proportion. However, each deletion has different effects on sterility of heterozygous males, withTor/tbeing fertile,Thp/tless fertile, andTorl/tstill less fertile. These data suggest that wild-type genes on chromosomes homologous to f-haplotypes can be important regulators of both TRD and fertility in males, and that the wild-type genes concerned with TRD and fertility are at least to some extent different. The data also provide a rough map of the positions of these genes.
Inheritance of T-associated sex reversal in mice
Authors: Washburn Linda L. , Lee Barbara K. , Eicher Eva M.
Published: September 2009

We previously identified a primary sex-determining locus,Tas, on mouse Chr 17 that causes ovarian tissue development in C57BL/6JThp/ + andTorl/ + individuals if the AKR/J Y chromosome is present. We hypothesized thatTasis located within the region of Chr 17 deleted byThpandTorland that C57BL/6J carries a diagnosticTasallele, based on the observation that ovarian tissue develops in XY mice whenThpis on a C57BL/6J inbred strain background, whereas normal testicular development occurs whenThpis on a C3H/HeSnJ inbred strain background. To test this hypothesis, we mated (C57BL/6J × C3H/HeSnJ)F1 females to C57BL/6JThp/ + hermaphrodites. As expected, half of the XYThp/+ offspring developed ovarian and testicular tissue while half developed exclusively testicular tissue. Unexpectedly, the inheritance of selected Chr 17 molecular loci was independent of gonadal development, as half of the male and hermaphroditic offspring inherited C3H/HeSnJ-derived Chr 17 loci and half inherited C57BL/6J-derived Chr 17 loci. We conclude that for ovarian tissue to develop in an XYThp/ + or XYTort/ + individual (1)Tasmust be present in a hemizygous state, which is accomplished by heterozygosity for theThporTortdeletions; (2) the AKR/J-derived Y chromosome must be present; and (3) an additional locus involved in primary sex determination must be present in a homozygous C57BL/6J state. This newly identified gene may be one of the previously defined loci,tda-1ortda-2.