Effects of a Locus Affecting Floral Pigmentation in Ipomoea Purpurea on Female Fitness Components

A locus influencing floral pigment intensity in the morning glory, Ipomoea purpurea, is polymorphic throughout the southeastern United States. Previous work has suggested that the white allele at this locus has a transmission advantage during mating because of the effect of flower color on pollinator behavior. The experiment described here was designed to determine whether other effects of the W locus may contribute an opposing selective advantage to the dark allele. Dark homozygotes were vegetatively smaller and produced fewer flowers, seed capsules and seeds than either light heterozygotes or white homozygotes. In addition, dark homozygotes produced smaller seeds than heterozygotes, and there is some indication that white homozygotes also produced smaller seeds than heterozygotes. Pleiotropic effects on seed number thus do not seem to contribute to selection opposing the mating advantage associated with the white allele. However, pleiotropic effects on seed size might contribute to overdominance that could stabilize the W locus polymorphism.     

Expression of Overdominance for Specific Activity at the Phosphoglucomutase-2 Locus in the Pacific Oyster, Crassostrea Gigas

Environmental and genetic components of specific activity variation at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas, were examined to assess the direct role played by this polymorphism in a heterozygosity/growth relationship. Both environmental variables studied, season and intertidal position, exerted highly significant effects on phosphoglucomutase specific activity but no interactions occurred between these factors and Pgm-2 genotype. Highly significant differences were also detected between Pgm-2 genotypes. The three most common heterozygotes (Pgm-2(92/100), Pgm-2(96/100) and Pgm-2(100/104) consistently expressed greater specific activities than the Pgm-2(92/92), Pgm-2(96/96), Pgm-2(100/100) and Pgm-2(104/104) homozygotes. Overall, the specific activities of heterozygotes for the Pgm-2(100) allele exceeded heterozygotes by 24% and 20% in the mantle and adductor muscle tissues, respectively. Heterozygotes formed between the three less frequent Pgm-2(92), Pgm-2(96) and Pgm-2(104) alleles differed sharply from those possessing the Pgm-2(100) allele in being indistinguishable from homozygotes. The possibility of these patterns arising from the undetected presence of an inactive Pgm-2 allele was examined and found to be inconsistent with all of its predicted effects on the specific activity data. Genuine overdominance was shown to be capable of explaining the specific activities of ten structural locus genotypes, allelic frequency distributions in natural populations, and the maintenance of the enzyme polymorphism in a balanced state. The results provide evidence favoring the overdominance explanation for one locus involved in a heterozygosity/growth relationship and suggest that the reported effects of this locus on adult body weight may have been caused by the greater flux capacities of heterozygotes for the Pgm-2(100) allele.     

Electrophoretic evidence for disomic inheritance and allopolyploid origin of the octoploid Cerastium alpinum (Caryophyllaceae)

The mode of inheritance of six enzyme markers in the octoploid alpine plant Cerastium alpinum was analyzed. Offspring from crosses between heterozygotes showed fixed heterozygosity at malate dehydrogenase-2, phosphoglucoisomerase-2, triosephosphate isomerase-2, and triosephosphate isomerase-3. Phosphoglucomutase-1 also showed fixed heterozygosity except in offspring from one cross. Fixed heterozygosity in five enzyme systems suggests that C. alpinum has originated through at least some allopolyploidization. Offspring from plants heterozygous for two alleles at the menadione reductase-1 (Mr-1) locus did not deviate significantly from a 1:2:1 ratio. The large proportion of homozygotes suggests disomic inheritance because any kind of polysomic inheritance would result in a substantially increased proportion of heterozygotes relative to disomic inheritance. Assuming a diploid model for Mr-1, this locus was used to analyze the population genetic structure within C. alpinum populations. Inbreeding was found in many alpine populations. This may help explain the large genetic distances found among alpine populations in a previous study. The analysis is only based on one segregating locus, and the results should therefore be treated with caution. However, by establishing the mode of inheritance through crosses, we have been able to use a codominant marker in population genetic analysis of an octoploid plant.     

Hyperphenylalaninemia due to deficiency of 6-pyruvoyl tetrahydropterin synthase

Summary We have identified deficient biopterin synthesis in four probands and one sib with persistent postnatal hyperphenylalaninemia. The metabolic findings were associated with a benign clinical presentation and normal biopterin level in cerebrospinal fluid in the newborn period, indicating the peripheral (hepatic) form of this autosomal recessive phenotype. Impaired development was apparent at 3 months in one proband not treated early. Treatment with oral tetrahydropterin restored adequate phenylalanine hydroxylase activity; it also maintained or improved CNS function. The deficient enzyme in these subjects is 6-pyruvoyl tetrahydropterín synthase (PTS). Erythrocyte activity of PTS in homozygotes (or compound heterozygotes) is <10% of normal. Heterozygotes have 20%–50% of normal PTS activity (enzyme phenotype), a finding compatible with a range of gene dosage effects, some abnormal. The metabolic phenotype in heterozygotes (urine biopterin excretion) did not correlate with erythrocyte PTS activity. The complex relationship between erythrocyte PTS activity, and biopterin synthesis in these families indicates genetic heterogeneity at the PTS locus.Professor Niederwieser has unfortunately died since the paper was accepted     

HETEROZYGOSITY AND DEVELOPMENTAL RATE IN A STRAIN OF RAINBOW TROUT (SALMO GAIRDNERI)

Rainbow trout (Salmo gairdneri) with greater heterozygosity at enzyme loci also have greater developmental stability, as measured by bilateral symmetry of five meristic traits. Fish with increased amounts of liver phosphoglucomutase activity have greater developmental stability and develop faster than fish with normal activity. These observations suggest that the differences in developmental stability between homozygotes and heterozygotes may be the result of differences in developmental rate. Faster developmental rates are expected to decrease the probability of accidents during critical periods of development, resulting in a more stable or uniform phenotype. As indicated by differences in hatching time, heterozygotes tend to develop more rapidly than homozygotes. This association is not strongly expressed within families at any locus except Pgm1-t. However, heterozygotes for Mdh3,4 and Hex hatched significantly sooner than homozygotes in a population sample. These results suggest that differences in developmental rate between homozygotes and heterozygotes may account for the positive association between developmental stability and heterozygosity in rainbow trout.     

Interallelic Complementation at the sh Locus in Maize at the Enzyme Level

EMS-induced sh mutants and their heterozygotes were examined for the enzyme, sucrose synthetase, which has previously been shown to be coded by the Sh locus. Complementing heterozygotes have a wild-type phenotype, but show no hybrid protein band after starch gel electrophoresis. The existence of a heteromeric complex, however, is inferred from the two-fold elevation in sucrose cleavage activity in the complementing heterozygotes as compared to the mutant homozygotes. The observations on complementation described here are unique, as the elevation in the activity of this reversible enzyme is noticed only in one direction (viz, sucrose cleavage) of the reaction and not the other (sucrose synthesis).     

Haemolytic anaemia in Basenji dogs. 2. Partial deficiency of erythrocyte pyruvate kinase (PK; EC 2.7.1.40) in heterozygous carriers

Congenital nonspherocytic haemolytic anaemia (HA) in dogs of the Basenji breed is inherited as a simple, autosomal recessive trait. Previous results of pyruvate kinase (PK) assays suggest a causal relationship between the anaemia and PK deficiency in erythrocytes. In the present investigation assays of this enzyme have been performed on haemolysates from 45 Basenji dogs, comprising 3 anaemic and 42 non-anaemic individuals of which 13 were known heterozygotes. The PK activity in haemolysates from the 42 non-anaemic dogs exhibited a bimodal distribution corresponding to the genotypic classes: heterozygotes and normal homozygotes. The results indicate that heterozygotes have a partial, detectable enzyme deficiency, not reflected in clinical disease, and thus give evidence of a gene dosage effect in agreement with observations in man. The proposed genotypes PK PK, PK pk and pk pk refer to normal homozygotes, heterozygotes, and anaemic individuals, respectively. The findings strengthen the genetic hypothesis of recessiveness of the anaemia by direct detection of heterozygosity of parents of affected individuals. Moreover, the results are of value in comparative studies and they have practical application in connection with eradication programmes.     

In Candida albicans,white-opaque switchers are homozygous for mating type

The relationship between the configuration of the mating type locus (MTL) and white-opaque switching in Candida albicans has been examined. Seven genetically unrelated clinical isolates selected for their capacity to undergo the white-opaque transition all proved to be homozygous at the MTL locus, either MTLa or MTLalpha. In an analysis of the allelism of 220 clinical isolates representing the five major clades of C. albicans, 3.2% were homozygous and 96.8% were heterozygous at the MTL locus. Of the seven identified MTL homozygotes, five underwent the white-opaque transition. Of 20 randomly selected MTL heterozygotes, 18 did not undergo the white-opaque transition. The two that did were found to become MTL homozygous at very high frequency before undergoing white-opaque switching. Our results demonstrate that only MTL homozygotes undergo the white-opaque transition, that MTL heterozygotes that become homozygous at high frequency exist, and that the generation of MTL homozygotes and the white-opaque transition occur in isolates in different genetic clades of C. albicans. Our results demonstrate that mating-competent strains of C. albicans exist naturally in patient populations and suggest that mating may play a role in the genesis of diversity in this pernicious fungal pathogen.     

Linear dominance relationship among four class-II S haplotypes in pollen is determined by the expression of SP11 in Brassica self-incompatibility

Self-incompatibility (SI) prevents self-fertilization by rejecting pollen from plants with the same S phenotype. The Brassica SI system is controlled sporophytically by multiple alleles at the single locus, S, and dominance relationships among S haplotypes are observed in both stigma and pollen. We have identified previously five different class-II S haplotypes in Brassica campestris. Here, we performed test-crosses between S heterozygotes and their respective parental S homozygotes for four of these class-II S haplotypes, and observed a linear dominance relationship on the pollen side. To determine how this relationship is controlled, we performed RNA gel blot analyses for six S heterozygotes and their respective parental S homozygotes using the corresponding SP11 clone as a probe. In all six S heterozygotes, SP11 derived from a dominant haplotype was predominantly expressed, and SP11 derived from a recessive haplotype was repressed. Thus, the linear dominance relationship of the SI phenotype on the pollen side is regulated by the expression of SP11.     

Homozygotes for the autosomal dominant neoplasia syndrome (MEN1).

Families in which both parents are heterozygotes for the same autosomal dominant neoplasia syndrome are extremely unusual. Recently, we had the unique opportunity to evaluate three symptomatic siblings from the union between two unrelated individuals affected by multiple endocrine neoplasia type 1 (MEN1). When the three siblings and their parents and relatives were genotyped for 12 markers tightly linked to the MEN1 locus, at 11q13, two of the siblings were found to be homozygotes, and one a heterozygote, for MEN1. With regard to the MEN1 syndrome, no phenotypic differences were observed between the two homozygotes and the heterozygotes. However, the two homozygotes showed unexplained infertility, which was not the case for any of the heterozygotes. Thus, MEN1 appears to be a disease with complete dominance, and the presence of two MEN1 alleles with mutations of the type that occur constitutionally may be insufficient for tumor development.     

Genetically-based trade-offs in response to stoichiometric food quality influence competition in a keystone aquatic herbivore

The genetic basis of organism response to stoichiometric mismatches between environmental availability and somatic demand is still poorly understood. This study reports a consistent genotype × environment interaction related to phosphorus : carbon availability to Daphnia . In multiple pairs of Daphnia pulicaria clones, genetic variation at the phosphoglucose isomerase ( Pgi ) locus indicated that Pgi- heterozygotes out competed Pgi -homozygotes under high P : C conditions, whereas the opposite outcome was observed under low P : C conditions. Estimates of phosphorus use efficiency indicated that homozygotes were significantly more efficient. However, homozygotes were comparatively less homeostatic. We hypothesize that lower specific activity of Pgi from homozygotes, which results in lowered energetic efficiency during the second glycolytic step, may underlie the competitive advantage enjoyed by homozygotes under low P : C (i.e. excess C) conditions. Our results show that analysing stoichiometric mismatches between diet and consumer should advance our quest for a fundamental understanding of the mechanisms driving genotype-environment interactions.     

Haemolytic anaemia in Basenji dogs. 2. Partial deficiency of erythrocyte pyruvate kinase (PK; EC 2.7.1.40) in heterozygous carriers1

Congenital nonspherocytic haemolytic anaemia (HA) in dogs of the Basenji breed is inherited as a simple, autosomal recessive trait. Previous results of pyruvate kinase (PK) assays suggest a causal relationship between the anaemia and PK deficiency in erythrocytes. In the present investigation assays of this enzyme have been performed on haemolysates from 45 Basenji dogs, comprising 3 anaemic and 42 non-anaemic individuals of which 13 were known heterozygotes. The PK activity in haemolysates from the 42 non-anaemic dogs exhibited a bimodal distribution corresponding to the genotypic classes: heterozygotes and normal homozygotes. The results indicate that heterozygotes have a partial, detectable enzyme deficiency, not reflected in clinical disease, and thus give evidence of a gene dosage effect in agreement with observations in man. The proposed genotypes PK PK, PK pk and pk pk refer to normal homozygotes, heterozygotes, and anaemic individuals, respectively. The findings strengthen the genetic hypothesis of recessiveness of the anaemia by direct detection of heterozygosity of parents of affected individuals. Moreover, the results are of value in comparative studies and they have practical application in connection with eradication programmes.     

Differential performance among LDH-B genotypes in Rana lessonae tadpoles

The European pool frog, Rana lessonae, is widely polymorphic for two common alleles (b,e) at the lactate dehydrogenase-B (LDH-B) locus. We compared fitness-related larval life-history traits among LDH-B genotypes, which originated from segregation in heterozygous parents, in an artificial pond experiment where tadpoles of R. lessonae from a Swiss population were raised together with tadpoles of the hemiclonal hybrid R. esculenta at two densities. In R. lessonae, LDH-B e/e homozygotes at each density had a higher proportion of metamorphs among survivors, reached metamorphosis earlier, and were heavier at metamorphosis than b/b homozygotes; b/e heterozygotes had intermediate values. That e/e individuals were superior to b/b in both time to and mass at metamorphosis is surprising because these two life-history traits are thought to reflect a performance trade-off; e/e genotypes apparently compensated for shorter time to metamorphosis by a higher growth rate. The two alleles showed the same performance ranking when combined in hybrids with a R. ridibunda allele: When R. esculenta from Swiss populations reared in the same ponds had received the e allele rather than the b allele from their R. lessonae parent, they reached metamorphosis earlier, but did not differ in mass at metamorphosis. The degree of linkage disequilibrium in the source population of the eight R. lessonae used as parents of the R. lessonae tadpoles is unknown, so we cannot exclude the possibility that the performance differences are caused by some anonymous tightly linked gene, rather than the LDH-B locus, that constitutes the genomically localized target of natural selection. A causal involvement of LDH-B is plausible, nevertheless, because this enzyme takes part in the central energy-metabolizing processes and has been reported to underlie fitness differences in other animals; also, differential performance of LDH-B genotypes has been observed in R. lessonae larvae from another population. The present results suggest strong directional selection for allele e; the sum of available data, including an independent laboratory experiment, suggests that partial environment-dependent overdominance combined with balancing selection favoring e/e homozygotes under some and b/b homozygotes under other conditions may be partially responsible for the broad maintenance of the LDH-B polymorphism in R. lessonae.     

Blood pressure cosegregates with a microsatellite of angiotensin I converting enzyme (ACE) in F2 generation from a cross between original normotensive Wistar-Kyoto rat (WKY) and stroke-prone spontaneously hypertensive rat (SHRSP).

We investigated the linkage between high blood pressure and the ACE gene in the F2 generation between SHRSP/Izm and WKY/Izm. The male F2 rats were categorized into 3 genotypes according to a microsatellite polymorphism in the ACE gene. Significantly high blood pressure was observed in the SHRSP homozygotes when it was compared to the blood pressure of the heterozygotes. Further, after 2 or 3 months salt-loading, the blood pressure was significantly higher in the SHRSP homozygotes than in the heterozygotes and the WKY homozygotes. The heterozygotes had a blood pressure similar to that in the WKY homozygotes, indicating that the effect of the ACE gene genotype was recessive. Salt appetite was neither correlated with the salt-sensitivity nor cosegregated with the ACE genotype. The results indicate that the locus of ACE gene associates with the development of hypertension, especially salt-sensitive hypertension.     

PCR-RFLP和测交方法对进口祖代蛋鸡异性个体间的遗传同质性检测

对进口Ｘ祖代鸡Ｂ系和Ｄ系共１４３羽异性公鸡的Ｋ座位羽速型作了Ｋ座位隐性测交,杂合子占４１．９６％,慢羽纯合子占３５．６６％,另有９羽和２羽公鸡分别因后裔数少于７羽或是后裔快慢羽鸡比例严重偏离１：１而被判为无效,对８羽进口祖代Ｄ系异性公鸡的ＰＣＲ－ＲＦＬＰ分析的结果表明,６羽公鸡为Ｋ座位显性纯合子（仅检到１４５０ｂｐＤＮＡ片段）,２羽为杂合子（检到１４５０ｂｐ、１０６８ｂｐ和３８２ｂｐ共３条带）。通     

Pericentric inversion in natural populations of Oligoryzomys nigripes (Rodentia: Sigmodontinae).

We analysed polymorphism for pericentric inversion in chromosome 3 of Oligoryzomys nigripes (Rodentia: Sigmodontinae) in several populations in Brazil and examined the meiotic behaviour of this chromosome in heterozygotes. We observed an orderly pairing of all chromosomes at pachytene in heterozygotes for the inverted chromosome 3. No indication of meiotic arrest and germ-cell death was found. Electron microscopy of synaptonemal complexes and conventional meiotic analysis indicated strictly nonhomologous synapsis and crossing-over suppression in the inverted region in the heterozygotes, which prevent the formation of unbalanced gametes. Thus, the pericentric inversion in chromosome 3 does not apparently result in any selective disadvantages in heterozygous carriers. In the majority of the populations studied, the frequencies of acrocentric homozygotes, metacentric homozygotes, and heterozygotes were in Hardy-Weinberg equilibrium. However, in some populations, we detected an excess of heterozygotes and a deficiency of acrocentric homozygotes.     

Biochemical studies of supernatant malate dehydrogenase allozymes in Drosophila melanogaster.

1. A biochemical comparison was made among cytoplasmic malate dehydrogenase allozymic variants from Drosophila melanogaster. Experiments were carried out on enzyme extracted from six different genotypes: three homozygotes and their respective heterozygotes. 2. The allozyme forms (MDH A, MDH B, MDH C) were indistinguishable in terms of NAD and L-malate optima, while they are distinguishable in terms of NADH and OAA saturation conditions. Activities were inhibited at concentrations greater than 0.36 and 0.40 mM NADH for BB and AA, CC, respectively, while in relation to OAA inhibition was observed at concentrations higher than 3 or 6 mM for the AA, CC and BB, respectively. 3. differences among genotypes were also observed in thermal stability: Km values for OAA, L-malate, NADH and NAD: and pG optima. 4. A simple method is presented for the separation of the cytoplasmic from the mitochondrial malate dehydrogenase.     

Golden: a novel coat color mutant in the wild mouse Mus caroli

We identified a spontaneous pigmentation mutant in the wild mouse species Mus caroli. Mutant mice exhibit a golden coat color on the agouti background, easily distinguishable from the darker wild type. The golden phenotype segregates as an autosomal recessive, showing no linkage to the sex-linked enzyme marker glucose-6-phosphate dehydrogenase. Obligate heterozygotes are phenotypically indistinguishable from the wild type. At birth, homozygotes have poorly pigmented eyes, which darken with age to become indistinguishable from the wild type. Pigmentation of the ears, tail, and footpads is reduced in intensity. Preliminary studies indicate that the phenotype may be due to an alteration in the shape and pigmentation of the eumelanosomes. The viability and fertility of both heterozygotes and homozygotes, as measured by litter size, sex ratio, or frequency of survival to weaning, appear to be normal for M. caroli. Spectrophotometric analysis of hair samples from the mouse variant at the putative golden locus (gdn) suggests that this mutant is not homologous to at least six independent pigment mutants previously identified in M. musculus.     

The Genetic Structure of Natural Populations of Drosophila melanogaster. Xx. Comparison of Genotype-Environment Interaction in Viability between a Northern and a Southern Population

In order to examine the operation of diversifying selection as the maintenance mechanism of excessive additive genetic variance for viability in southern populations in comparison with northern populations of Drosophila melanogaster, two sets of experiments were conducted using second chromosomes extracted from the Ogasawara population (a southern population in Japan) and from the Aomori population (a northern population in Japan). Chromosomal homozygote and heterozygote viabilities were estimated in eight kinds of artificially produced breeding environments. The main findings in the present investigation are as follows: (1) Significant genotype-environment interaction was observed using chromosomes extracted from the Ogasawara population. Indeed, the estimate of the genotype-environment interaction variance for heterozygotes was significantly larger than that of the genotypic variance. On the other hand, when chromosomes sampled from the Aomori population were examined, that interaction variance was significant only for homozygotes and its value was no more than one quarter of that for the chromosomes from the Ogasawara population. (2) The average genetic correlation between any two viabilities of the same lines estimated in the eight kinds of breeding environments for the chromosomes sampled from the Ogasawara population was smaller than that for the chromosomes from the Aomori population both in homozygotes and in heterozygotes, especially in the latter. (3) The stability of heterozygotes over homozygotes against fluctuations of environmental conditions was seen in the chromosomes from the Ogasawara population, but not from the Aomori population. (4) From the excessive genotype-environment interaction variance compared with the genotypic variance in heterozygotes, it was suggested for the chromosomes from the Ogasawara population that the reversal of viability order between homozygotes took place in some environments at the locus level. On the basis of these findings, it is strongly suggested that diversifying selection is operating in a southern population of D. melanogaster on some of the viability polygenes which are probably located outside the structural loci, and the excessive additive genetic variance of viability in southern populations is maintained by this type of selection.     

Heterosis in a wild strain of Drosophila polymorpha with a lethal closely linked to the major esterase locus

A laboratory population derived from a single wild inseminated female has a lethal so closely linked to the major esterase locus that in 3 years of observations no crossover products have been detected. Linkage with a chromosome inversion was excluded by cytological analysis. The heterozygotes are superior to the homozygotes in egg-adult viability, egg-laying rate, and longevity. Electrophoretic analysis of larvae, pupae, and 2-h-old adults shows that the specific phase for the lethal effect in homozygotes is the pupal stage.