Enzyme heterozygosity and growth of rainbow trout reared at two rations

The relationship between heterozygosity at nine enzyme loci and both size and growth in rainbow trout ( Salmo gairdneri ) reared at either low (LRT) or high (HRT) ration for 84 days is reported. The experimental fish were progeny produced from a pooled mating of 25 female and 25 male rainbow trout captured in spawning condition at the Ganaraska River, Ontario. There is a significant negative regression between the number of heterozygous loci per fish and size (fork length and weight) among fish at the beginning of the experiment. Heterozygotes at two loci, Sod and Mdh3,4 , were significantly smaller than homozygotes. A significant negative regression between multilocus heterozygosity and size was detectable among the fish reared at HRT for 84 days but not at LRT. Ration appeared to affect the strength of the association between heterozygosity and growth because at HRT homozygotes at the majority of loci grew faster than heterozygotes, but the reverse was true at LRT.     

Linkage relationships among five enzyme-coding gene loci in the copepod Tigriopus californicus: A genetic confirmation of achiasmatic meiosis

Linkage relationships among five polymorphic enzyme-coding gene loci in the marine copepod Tigriopus californicus have been determined using electrophoretic analysis of progeny from laboratory matings. Phosphoglucose isomerase (PGI; EC 5.3.1.9) was found to be tightly linked to glutamate-pyruvate transaminase (GPT; EC 2.6.1.2), with only one recombinant observed in 364 progeny; glutamate-oxaloacetate transaminase (GOT; EC 2.6.1.1) is linked to the PGI-GPT pair, with a recombination fraction of approximately 0.20 in male double heterozygotes. Phosphoglucomutase (PGM; EC 2.7.5.1) and an esterase (EST; EC 3.1.1.1) are not linked to the PGI, GPT, GOT grouping, which has been designated linkage group I. Reciprocal crosses have revealed that no recombination occurs in female T. californicus; this observation confirms a previous report that meiosis in female Tigriopus is achiasmatic.     

Transition from a heterozygous to a homozygous state of a pair of loci in the inverted repeat sequences of the L component of the herpes simplex virus type 1 genome.

The behavior of herpes simplex virus type 1 heterozygous isolates, in which the two inverted repeats of the L component (RL) were differentiated by a polymorphism marker (the presence [type B] or absence [type A] of a SalI site), was investigated. The progeny viruses derived from the heterozygote (A/B) consisted of heterozygotes (A/B), type A homozygotes (A/A), and type B homozygotes (B/B). The heterology between RL, albeit tolerated, was unstable, as is the case with heterology between the repeats of the S component. The two repeats TRL (terminal) and IRL (internal) were equipotent in generating homozygotes from a heterozygote. Data obtained from an analysis of 426 progeny viruses derived from heterozygous clones supported the hypothesis that the two loci in RL of a herpes simplex virus type 1 genome are determined as a random combination of the corresponding two loci in RL of the parent virus and that the ratio of heterozygotes/type A homozygotes/type B homozygotes in the progeny viruses from a heterozygote is expected to be 2:1:1. An ephemeral dominance of one type of homozygote over the other was observed in subclones from several heterozygous clones.     

Genic heterogeneity and genetic monitoring of mouse outbred stocks.

An outbred stock of Swiss:SE mice has been surveyed for genic heterogeneity at 12 loci, encoding biochemical polymorphisms in mice. Using horizontal starch-gel electrophoresis, 6 loci (Es-1, Es-2, Es-3, Es-5, Trf, Dip-1) revealed no genic heterogeneity within the total sample of 289 male mice examined. The other 6 loci (Mpi-1, Mup-1, Hbb, Gpi-1, Pgm-1, Ldr-1) each showed a 2-allelic variation within each of the 3 stock units (pavillions) involved. A pavillion effect on the observed genotype numbers was found for Pgm-1 and Gpi-1 (P less than 0.10). Inadequate genotyping may have occurred at Gpi-1 and Ldr-1, as suggested by a 'week effect' on the observed genotype numbers (P less than 0.05). For studying long-term genetic changes within outbred stocks, a routine monitoring procedure using biochemical polymorphisms is recommended.     

Two Sex-Linked Loci in the Leopard Frog, RANA PIPIENS

Crosses involving one heterozygous parent were performed to test the inheritance of enzymes in the leopard frog, Rana pipiens. After metamorphosis, offspring were sexed and tissue extracts from them were analyzed by gel electrophoresis. Enzyme genotype and sex showed independent assortment for 10 of 12 enzymes heterozygous in the male parent. However, among the offspring of males heterozygous for peptidase C (Pep-C) or superoxide dismutase 1 (SOD-1), male progeny tend to inherit one allele, whereas female progeny tend to inherit the other. Data from several different crosses yield recombination frequencies of 8.6% between sex and SOD-1, 6.9% between SOD-1 and Pep-C and 12.1% between sex and Pep-C. When the female parent is heterozygous for these enzymes no significant difference is seen, in the offspring, between male and female homozygotes and heterozygotes. These results confirm that males are the heterogametic sex in R. pipiens and suggest that sex is determined by a small number of genes on otherwise identical X and Y chromosomes.     

Inheritance of microsatellite DNA in bisexual gynogenesis complex of Fangzheng silver crucian carp,Carassius auratus gibelio (Bloch)

Five gynogenetic progeny groups of silver crucian carp Carassius auratus gibelio were produced and sex ratios (males:total progeny) of each of the progeny groups were analysed. About 110 males and 366 females were genotyped at 15 microsatellite loci for comparison with their parents to (1) verify the gynogenesis status of Fangzheng C. auratus gibelio, (2) detect the incorporation of paternal genetic material into the offspring and (3) study the possible association of genetic exchange at microsatellite loci with the existence of sex. The sex ratios in progenies of five groups were highly variable, but all had significant female bias. The sex ratio ranged from 0 to 0·37. Significant differences in the sex ratio within and between groups were also found. Microsatellite genotyping at 15 loci showed that 100 and 97% of the progeny shared the same genotype with the mother in four groups and in one group, respectively, confirming that gynogenesis is the general mechanism of reproduction in C. auratus gibelio. However, 0·63% of all offspring did show incorporation of paternal genetic material. No single loci tested were associated with the occurrence of male progeny, indicating unknown genetic mechanisms for sex determination in C. auratus gibelio.     

Recombinant genotypes in backcrosses of male Atlantic salmon × brown trout hybrids to female Atlantic salmon

When male hybrids of Atlantic salmon × brown trout were backcrossed to female Atlantic salmon, approximately 1% of diploid progeny hatched. These were shown to exhibit recombinant genotypes when examined electrophoreticalty at five enzyme loci. This is the first confirmation of genie recombination in backcrosses of these species. Triploidization greatly increases the proportion of backcross progeny which hatch.     

Genetic Analysis of Esterase Polymorphism in the Soybean Cyst Nematode, Heterodera glycines

The genetic basis of esterase polymorphism in Heterodera glycines was investigated through controlled matings and analysis of F₁ and F₂ progeny. Three nematode lines, each fixed for a different esterase phenotype, were isolated and purified through repeated directional selection and inbreeding. Each phenotype was characterized by its distinct pair of closely spaced bands of esterase activity. Single-female single-male crosses were conducted according to a modified agar-plate mating technique. F₁ progeny were homogeneous, exhibiting both parental esterase phenotypes (codominant heterozygotes) but no hybrid bands. Approximately 1,500 F₂ progeny segregated in a 1:2:1 ratio for expression of the esterase phenotypes of the female parental line, the heterozygote, and the male parental line. Apparently the three esterase phenotypes correspond to three codominant alleles of a single esterase locus. Reciprocal crosses gave similar results, suggesting no maternal inheritance.     

Inheritance of random amplified polymorphic DNA markers in cassava (Manihot esculenta Crantz)

The informativeness and inheritance of randomly amplified polymorphic DNA (RAPD) markers were investigated in an intraspecific F1 progeny derived from two heterozygous parents. The analysis confirmed the utility of RAPD markers for comparing candidate parents for the development of a molecular genetic map, and provided numerous markers for linkage analysis in a crop with a very limited history of classical or molecular genetic studies. Six potential parental lines (themselves F1 hybrid clones) showed between 1.82 and 0.62 segregating bands per primer in three hybrid families. Forty-three percent (309) of 722 primers produced polymorphic products in the most informative of these three crosses, revealing 328 single-dose (SD) markers segregating 1:1 for presence/absence in a progeny of 90 individuals. A second class of informative markers were those present in both parents but segregating in the progeny. Fifty-seven or 67% of the monomorphic but segregating markers exhibited the 3:1 ratio expected for SD dominant markers in a cross between heterozygotes. Linkage groups were constructed from the segregation of SD RAPD markers originating in the female (TMS 30572) and the male (CM2177-2) parent. Key words : RAPDs, molecular markers, genetic segregation, Manihot, single-dose markers.     

Multiple paternity in <Emphasis Type="Italic">Rhipicephalus</Emphasis> (<Emphasis Type="Italic">Boophilus</Emphasis>) <Emphasis Type="Italic">microplus</Emphasis> confirmed by microsatellite analysis

The aim of this study was to determine if individual ticks among the progeny of a single female Rhipicephalus (Boophilus) microplus tick removed from cattle under natural conditions are the result of mating with one or several males. To this end, simulations were run using an existing dataset of genotypes from 8 microsatellite loci to predict the number of samples required and the best locus. Subsequently, 14–22 progeny from each of 15 engorged female ticks removed from three cows, and the engorged females themselves, were genotyped for the BmM1 locus and the minimum number of potential male parents was determined for each progeny group. Of the 15 progeny groups, 10 must have been sired by more than one male, as indicated by the presence of five unique alleles among the progeny or three unique alleles that could not have been contributed by the female. This finding demonstrates multiple paternity in R. microplus.     

Determination of Quantitative Trait Loci (QTL) for Early Maturation in Rainbow Trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

To identify quantitative trait loci (QTL) influencing early maturation (EM) in rainbow trout (Oncorhynchus mykiss), a genome scan was performed using 100 microsatellite loci across 29 linkage groups. Six inter-strain paternal half-sib families using three inter-strain F(1) brothers (approximately 50 progeny in each family) derived from two strains that differ in the propensity for EM were used in the study. Alleles derived from both parental sources were observed to contribute to the expression of EM in the progeny of the brothers. Four genome-wide significant QTL regions (i.e., RT-8, -17, -24, and -30) were observed. EM QTL detected on RT-8 and -24 demonstrated significant and suggestive QTL effects in both male and female progeny. Furthermore, within both male and female full-sib groupings, QTL on RT-8 and -24 were detected in two or more of the five parents used. Significant genome-wide and several strong chromosome-wide QTL for EM localized to different regions in males and females, suggesting some sex-specific control. Namely, QTL detected on RT-13, -15, -21, and -30 were associated with EM only in females, and those on RT-3, -17, and -19 were associated with EM only in males. Within the QTL regions identified, a comparison of syntenic EST markers from the rainbow trout linkage map with the zebrafish (Danio rerio) genome identified several putative candidate genes that may influence EM.     

Linkage between one of the polygenic hexythiazox resistance genes and an etoxazole resistance gene in the twospotted spider mite (Acari: Tetranychidae)

Genetic linkage between hexythiazox and etoxazole resistance loci was analyzed by crossing experiments. Two strains, one resistant (R) and the other susceptible (S) to both chemicals were established from field-collected Tetranychus urticae Koch (Acari: Tetranychidae) populations that were further selected in the laboratory. To analyze the recombination rate of the loci associated with resistance, we tested the ovicidal effects of a mixed solution of hexythiazox and etoxazole on haploid F2 eggs laid by F1 females from an R female x S male cross. This revealed tight or complete linkage between the hexythiazox and etoxazole resistance loci. We then assessed the number of loci associated with resistance to each acaricide based on mortality in the haploid F3 progeny (eggs) of F2 females from an F1 female (R x S) x S male testcross. The mortality rate indicated that etoxazole resistance was largely controlled by a single major locus, whereas hexythiazox resistance was controlled by more than one locus. Thus, one hexythiazox resistance locus was tightly or completely linked to the etoxazole resistance locus.     

RFLP linkage map of asparagus.

A population resulting from a double pseudotestcross of two outbred-derived asparagus (Asparagus officinalis L.) clones was evaluated by RFLP (restriction fragment length polymorphism) analysis to produce individual maps of the male and female parents. An asparagus PstI genomic library was created and used as the source of probes. Scoring of bands was done by examining SDRFs (single dose restriction fragments) that are present in one parent and absent in the other and segregate 1:1 in the progeny. The data were analyzed as a backcross population; inversion or recoding allowed for the detection of repulsion phase linkage. The male parent map consisted of 33 loci in 10 groups, while the female parent map had 48 loci arranged in 14 groups. Segregation distortion was minimal (5%), and 17% of the markers were found to be unlinked. Loci of the configuration a/b x a/b and a/c x b/c were used to bridge seven homologous linkage groups between the two parents. The sex locus was not found to be associated with any linkage group. Key words : RFLP, bridge loci, repulsion phase linkage, double pseudotestcross.     

A Preliminary Genetic Linkage Map of the Pacific Abalone Haliotis discus hannai Ino

Preliminary genetic linkage maps were constructed for the Pacific abalone (Haliotis discus hannai Ino) using amplified fragment length polymorphism (AFLP), randomly amplified polymorphic DNA (RAPD), and microsatellite markers segregating in a F₁ family. Nine microsatellite loci, 41 RAPD, and 2688 AFLP markers were genotyped in the parents and 86 progeny of the mapping family. Among the 2738 markers, 384 (including 365 AFLP markers, 10 RAPD markers, and 9 microsatellite loci) were polymorphic and segregated in one or both parents: 241 in the female and 146 in the male. The majority of these markers, 232 in the female and 134 in the male, segregated according to the expected 1:1 Mendelian ratio (α = 0.05). Two genetic linkage maps were constructed using markers segregating in the female or the male parent. The female framework map consisted of 119 markers in 22 linkage groups, covering 1773.6 cM with an average intermarker space of 18.3 cM. The male framework map contained 94 markers in 19 linkage groups, spanning 1365.9 cM with an average intermarker space of 18.2 cM. The sex determination locus was mapped to the male map but not to the female map, suggesting a XY-male determination mechanism. Distorted markers showing excess of homozygotes were mapped in clusters, probably because of their linkage to a gene that is incompatible between two parental populations.     

Gnome and other effects of a small translocation in the mouse

A semisterile F1 male mouse from an X-ray experiment produced about 25 percent lethal gnome young in outcrosses. These animals were about half normal size, with short tail and small eyes, and died at birth. Surviving progeny were of four classes: 1) like the sire, 2) semisterile, 3) normal, and 4) gnome-producing, but not semisterile. Two independent reciprocal translocations have been identified from the original male, one of the classic type giving semisterile heterozygotes and involving chromosomes 5 and 15. The second translocation seems to be very small, giving the gnome type as one duplication-deficiency product, and the other unbalanced type seeming to pass for normal, although large body size and occasional agnathism may be produced. The small translocation has been found linked with the loci of v (waltzing) and Sl (steel) on chromosome 10. Cytological study has not revealed obvious structural changes. The translocation is now maintained in the homozygous state. The designation T(10;?)2Ho is proposed.     

RAPD和SSR两种标记构建的中国对虾遗传连锁图谱

利用RAPD和SSR分子标记结合拟测交策略,对中国对虾(Fenneropenaeuschinensis)“黄海1号”雌虾与野生雄虾作为亲本进行单对杂交产生的F1代,采用RAPD和SSR两种分子标记技术初步构建了中国对虾雌、雄遗传连锁图谱。对460个RAPD引物和44对SSR引物进行筛选,共选出61个RAPD引物和20对SSR引物,用于对父母本和82个F1个体进行遗传分析。共得到母本分离标记146个(RAPD标记128个,微卫星标记18个)和父本分离标记127个(RAPD标记109个,微卫星标记18个)。雌性图谱包括8个连锁群、9个三联体和14个连锁对,标记间平均间隔为11·28cM,图谱共覆盖1173cM,覆盖率为59·36%;雄性图谱包括10个连锁群、12个三联体和7个连锁对,标记间平均间隔为12·05cM,图谱共覆盖1144·6cM,覆盖率为62·01%。中国对虾遗传图谱的构建为其分子标记辅助育种、比较基因组作图及数量性状位点的定位与克隆奠定了基础。     

Serial backcross analysis of genetic resistance to mousepox, using marker loci for Rmp-2 and Rmp-3.

At least three genes from C57BL/6 mice that mediate dominant resistance to lethal mousepox were isolated and transferred onto a susceptible DBA/2 background. Three [(C57BL/6 x DBA/2)F1 x DBA/2] male mice that survived infection were selected as founders on the basis of different complements of marker loci for two resistance genes, Rmp-2r (Hc1) and Rmp-3r (H-2Db). They were crossed with DBA/2 mice, male progeny were infected with ectromelia virus, and the cycle was repeated with surviving male progeny through seven backcross generations. Two founders carried a marker locus for Rmp-2r or Rmp-3r, and the third carried neither marker locus. Resistance pedigrees were analyzed for passage of marker loci. From the three founders, resistance was passaged through multiple generations, producing backcross lines with intermediate-male-resistance phenotypes (20% resistant). Females of backcross lines with intermediate male resistance had high resistance (> 50%). High-resistance backcross lines (40% male resistance) also developed from the founders that carried marker loci for Rmp-2r and Rmp-3r, and marker loci were passaged through all generations of high resistance but not intermediate-resistance lines. About one-third of all resistant mice in high-resistance lines sired by mice that carried marker loci for Rmp-2r and Rmp-3r did not carry the respective marker locus. In lines that carried Rmp-2r, this was apparently not the result of recombination between Rmp-2r and Hc1, because Rmp-2 was not in the predicted location on chromosome 2 and because mice that did not inherit Hc1 transmitted significantly less male resistance than Hc1-positive mice, although female resistance remained high. These results confirmed that C57BL/6 mice have redundant resistance mechanisms, two of which are controlled at least in part by Rmp-2r and Rmp-3r, and provided evidence for a fourth resistance gene, herein presumptively named Rmp-4, which protects females more than males and which may be epistatic to Rmp-2.     

Genetic assessment of the effects of self-fertilization in a Lilium L. hybrids using molecular cytogenetic methods (FISH and ISSR)

Self-fertilization (also termed selfing) is a mode of reproduction that occurs in hermaphrodites and has evolved several times in various plant and animal species. A transition from outbreeding to selfing in hermaphroditic flowers is typically associated with changes in flower morphology and functionality. This study aimed to identify genetic effects of selfing in the F2 progeny of F1 hybrid developed by crossing Lilium lancifolium with the Asiatic Lilium hybrid ‘Dreamland.’ Fluorescence in situ hybridization (FISH) and inter-simple sequence repeats (ISSR) techniques were used to detect genetic variations in plants produced by selfing. The FISH results showed that F1 hybrid were similar to the female parent (L. lancifolium) regarding the 45S loci, but F2 individuals showed variation in the number and location of the respective loci. In F2 progeny, F2-2, F2-3, F2-4, F2-5, and F2-8 hybrids expressed two strong and one weak 5S signal on chromosome 3, whereas F2-7 and F2-9 individuals expressed one strong and two weak signals. Only two strong 5S signals were detected in an F2-1 plant. The ISSR results showed a maximum similarity value of 0.6269 between the female parent and the F2-2 hybrid. Regarding similarity to the male parent, a maximum value of 0.6119 was found in the F2-1 and F2-2 hybrids. The highest genetic distance from L. lancifolium and the Asiatic Lilium hybrid ‘Dreamland’ was observed in the F2-4 progeny (0.6352 and 0.7547, respectively). Phylogenetic relationships showed that the F2 progeny were closer to the male parent than to the female parent. Self-fertilization showed effects on variation among the F2 progeny, and effects on the genome were confirmed using FISH and ISSR analyses.     

A first genetic linkage map of mulberry (Morus spp.) using RAPD, ISSR, and SSR markers and pseudotestcross mapping strategy

To lay the foundation for molecular breeding efforts, the first genetic linkage map of mulberry (2n=2x=28) was constructed with 50 F1 full-sib progeny using randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), and simple sequence repeat (SSR) markers and two-way pseudotestcross mapping strategy. We selected 100 RAPD, 42 ISSR, and 9 SSR primers that amplified 517 markers, of which 188 (36.36%) showed a test-cross configuration, corresponding to the heterozygous condition in one parent and null in the other. Two separate female and male maps were constructed using 94 each of female- and male-specific testcross markers, containing 12 female linkage groups and 14 male linkage groups. At a minimum logarithm of the odds (LOD) score threshold of 6.0 and at a maximum map distance of 20 cM, the female map covered a 1,196.6-cM distance, with an average distance of 15.75 cM and maximum map distance of 37.9 cM between two loci; the male-specific map covered a 1,351.7-cM distance, with an average distance of 18.78 cM and a maximum map distance between two loci is of 34.7 cM. The markers distributed randomly in all linkage groups without any clustering. All 12 linkage groups in the female-specific map consisted of 4–10 loci ranging in length from 0 to 140.4 cM, and in the male-specific map, the 13 largest linkage groups (except linkage group 12, which contained three loci) consisted of 4–12 loci, ranging in length from 53.9 to 145.9 cM and accounting for 97.22% of the total map distance. When mapping, progeny pass through their juvenile phase and assume their adult characters, mapping morphological markers and identification of quantitative trait loci for adaptive traits will be the primary target. In that sense, our map provides reference information for future molecular breeding work on Morus and its relatives.     

Genetic diversity in Cucumis sativus L. assessed by variation at 18 allozyme coding loci

Summary The genetic diversity of the U.S. Cucumis sativus L. germplasm collection [757 plant introductions (PI) representing 45 countries] was assessed using 40 enzymes which represented 74 biochemical loci. Polymorphisms were observed at 18 loci (G2dh-1, Gpi-1, Gpi-2, Gr-1, Gr-2, Idh, Mdh-1, Mdh-2, Mdh-3, Mpi-2, Pepla-2, Peppap-2, Per-4, Pgd-1, Pgd-2, Pgm-1, Pgm-3, and Skdh). Two PIs (285606 and 215589) contained alleles [G2dh-1(1) and Per-4(2), respectively] which did not occur in any other PI. Other alleles which occurred in low frequencies (in < 1% of the PIs) included Gpi-1(3), Gpi-2(3), Gr-1(3), Gr-2(1), Idh(1), Mdh-1(2), Mdh-2(1), Peppap-2(1), and Pgd-1(1). Individual loci containing more than one allele in greater than 20% of the PIs included Mpi-2, Pepla-2, Pgd-2, and Pgm-1. Multivariate analyses aided in the reduction of data (principle components), depicted relationships among PIs (cluster), and identified the most discriminating enzyme loci (Pgm-1, Pepla-2, Gr-1, Pgd-2, Mpi-2, and Skdh) (classification and regression tree).Research partially supported by Asgrow, DeRuiter, Nickerson-Zwaan, Nunhems, and Sun Seed Companies; and the Graduate School, University of Wisconsin, Madison