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PubMed2001

An informative linkage map of soybean reveals QTLs for flowering time, leaflet morphology and regions of segregation distortion.

A genetic linkage map covering a large region of the genome with informative markers is essential for plant genome analysis, including identification of quantitative trait loci (QTLs), map-based cloning, and construction of a physical map. We constructed a soybean genetic linkage map using 190 F2 plants derived from a single cross between the soybean varieties Misuzudaizu and Moshidou Gong 503, based on restriction-fragment-length polymorphisms (RFLPs) and simple-sequence-repeat polymorphisms (SSRPs). This linkage map has 503 markers, including 189 RFLP markers derived from expressed sequence tag (EST) clones, and consists of 20 major linkage groups that may correspond to the 20 pairs of soybean chromosomes, covering 2908.7 cM of the soybean genome in the Kosambi function. Using this linkage map, we identified 4 QTLs--FT1, FT2, FT3, and FT4--for flowering time, the QTLs for the 5 largest principal components determining leaflet shape, 6 QTLs for single leaflet area, and 18 regions of segregation distortion. All 503 analyzed markers identified were located on the map, and almost all phenotypic variations in flowering time were explained by the detected QTLs. These results indicate that this map covers a large region of the soybean genome.

Chromosome Mapping↗
PubMed1992

Generation of a restriction fragment length polymorphism linkage map for Toxoplasma gondii.

We have constructed a genetic linkage map for the parasitic protozoan, Toxoplasma gondii, using randomly selected low copy number DNA markers that define restriction fragment length polymorphisms (RFLPs). The inheritance patterns of 64 RFLP markers and two phenotypic markers were analyzed among 19 recombinant haploid progeny selected from two parallel genetic crosses between PLK and CEP strains. In these first successful interstrain crosses, these RFLP markers segregated into 11 distinct genetic linkage groups that showed close correlation with physical linkage groups previously defined by molecular karyotype. Separate linkage maps, constructed for each of the 11 chromosomes, indicated recombination frequencies range from approximately 100 to 300 kb per centimorgan. Preliminary linkage assignments were made for the loci regulating sinefungin resistance (snf-1) on chromosome IX and adenine arabinoside (ara-1) on chromosome V by linkage to RFLP markers. Despite random segregation of separate chromosomes, the majority of chromosomes failed to demonstrate internal recombination events and in 3/19 recombinant progeny no intramolecular recombination events were detected. The relatively low rate of intrachromosomal recombination predicts that tight linkage for unknown genes can be established with a relatively small set of markers. This genetic linkage map should prove useful in mapping genes that regulate drug resistance and other biological phenotypes in this important opportunistic pathogen.

Animals↗
PubMed1998

An improved linkage map of rat chromosome 3 with three mapping panels.

Our purposes were to develop an improved linkage map for rat Chromosome 3 and to develop new markers polymorphic between Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats. The linkage mapping panel consisted of three F2 populations totaling 359 rats. Twenty-five new markers were developed and placed on the linkage map. About half of these markers (13) were polymorphic between S and R rats. The final map spans 124.7 centiMorgans (cM) and includes 64 markers. The average distance between adjacent markers is 1.9 cM, and the largest separation is 10.5 cM.

Animals↗
PubMed1997

Rat chromosome 1: regional localization of seven genes (Slc9a3, Srd5a1, Esr, Tcp1, Grik5, Tnnt3, Jak2) and anchoring of the genetic linkage map to the cytogenetic map.

Seven genes were regionally localized on rat Chromosome (Chr) 1, from 1p11 to 1q42, and two of these genes were also included in a linkage map. This mapping work integrates the genetic linkage map and the cytogenetic map, and allows us to orient the linkage map with respect to the centromere, and to deduce the approximate position of the centromere in the linkage map. These mapping data also indicate that the Slc9a3 gene, encoding the Na+/H+ exchanger 3, is an unlikely candidate for the blood pressure loci assigned to rat Chr 1. These new localizations expand comparative mapping between rat Chr 1 and mouse or human chromosomes.

Animals↗
PubMed1993

MultiMap: an expert system for automated genetic linkage mapping.

With the advent of the Human Genome Project, the ability to rapidly construct comprehensive and accurate linkage maps based on genetic marker data from family studies is an absolute necessity. In addition to their usefulness in localizing genes for both simple and complex disorders, linkage maps are invaluable tools for genetic counseling using linked marker genes. Several computer program packages are publicly available which aid in the construction of linkage maps by computing multipoint likelihoods for specified locus orders. However, these programs work in a step-by-step fashion, requiring intensive user-intervention and analysis at each step. Such a repetitive process is amenable to computerized automation. We have developed and tested an expert system computer program, MultiMap, for automated genetic linkage mapping. This program greatly reduces the amount of user-computer interaction, increasing the accuracy and speed with which a map can be constructed. In addition, because the total mapping time is greatly reduced through automation, it is now feasible to explore and compare various mapping heuristics and mapping criteria in order to develop the most appropriate approach, or set of approaches, for genetic linkage mapping. MultiMap need not be restricted to the construction of genetic maps, but could be adapted to aid in the automated construction of physical maps as well.

Automation↗
PubMed1997

Construction of a bovine chromosome 19 linkage map with an interspecies hybrid backcross.

Interspecific hybrid backcross animals from a Bos taurus x Bos gaurus F1 female were used to construct a linkage map of bovine Chromosome (Chr) 19. This map includes eight previously unmapped type I anchor loci, CHRNB1, CRYB1, GH1, MYL4, NF1, P4HB, THRA1, TP53, and five microsatellite markers, HEL10, BP20, MAP2C, ETH3, BMC1013, from existing linkage maps. The linkage relationship was determined to be centromere-HEL10-18.8cM-NF1-4.0cM-CRYB1-11 .2cM-(BP20, CHRNB1, TP53)-4.0cM-(MAP2C, GH1, MYL4, THRA1)-14.4cM-P4HB-11.2cM-ETH3-4. 0cM-BMC1013. It was previously revealed that bovine Chr 19 contains the largest known conserved autosomal synteny among human, bovine, and mouse. This study has shown that gene orders within this segment are not conserved among the three species. We propose structural changes in an ancestral mammalian chromosome to account for these differences. This is the first interspecific hybrid backcross used in bovine linkage studies, and it has proven to be an effective tool for incorporating bovine type I loci into the linkage map even with the small sample size presently available. This resource will facilitate the generation of comparative linkage maps that address gene order and effectively predict the locations of unmapped loci across species.

Animals↗
PubMed2006

Linkage maps for the Pacific abalone (genus Haliotis) based on microsatellite DNA markers.

This study presents linkage maps for the Pacific abalone (Haliotis discus hannai) based on 180 microsatellite DNA markers. Linkage mapping was performed using three F1 outbred families, and a composite linkage map for each sex was generated by incorporating map information from the multiple families. A total of 160 markers are placed on the consolidated female map and 167 markers on the male map. The numbers of linkage groups in the composite female and male maps are 19 and 18, respectively; however, by aligning the two maps, 18 linkage groups are formed, which are consistent with the haploid chromosome number of H. discus hannai. The female map spans 888.1 cM (Kosambi) with an average spacing of 6.3 cM; the male map spans 702.4 cM with an average spacing of 4.7 cM. However, we encountered several linkage groups that show a high level of heterogeneity in recombination rate between families even within the same sex, which reduces the precision of the consolidated maps. Nevertheless, we suggest that the composite maps are of significant potential use as a scaffold to further extend the coverage of the H. discus hannai genome with additional markers.

Animals↗
PubMed2006

A comparative linkage map of oilseed rape and its use for QTL analysis of seed oil and erucic acid content.

We have developed a new DH mapping population for oilseed rape, named TNDH, using genetically and phenotypically diverse parental lines. We used the population in the construction of a high stringency genetic linkage map, consisting of 277 loci, for use in quantitative genetic analysis. A proportion of the markers had been used previously in the construction of linkage maps for Brassica species, thus permitting the alignment of maps. The map includes 68 newly developed Sequence Tagged Site (STS) markers targeted to the homologues of defined genes of A. thaliana. The use of these markers permits the alignment of our linkage map with the A. thaliana genome sequence. An additional 74 loci (31 newly developed STS markers and 43 loci defined by SSR and RFLP markers that had previously been used in published linkage maps) were added to the map. These markers increased the resolution of alignment of the newly constructed linkage map with existing Brassica linkage maps and the A. thaliana genome sequence. We conducted field trials with the TNDH population at two sites, and over 2 years, and identified reproducible QTL for seed oil content and erucic acid content. The results provide new insights into the genetic control of seed oil and erucic acid content in oilseed rape, and demonstrate the utility of the linkage map and population.

Brassica napus↗
PubMed1987

MAPMAKER: an interactive computer package for constructing primary genetic linkage maps of experimental and natural populations.

With the advent of RFLPs, genetic linkage maps are now being assembled for a number of organisms including both inbred experimental populations such as maize and outbred natural populations such as humans. Accurate construction of such genetic maps requires multipoint linkage analysis of particular types of pedigrees. We describe here a computer package, called MAPMAKER, designed specifically for this purpose. The program uses an efficient algorithm that allows simultaneous multipoint analysis of any number of loci. MAPMAKER also includes an interactive command language that makes it easy for a geneticist to explore linkage data. MAPMAKER has been applied to the construction of linkage maps in a number of organisms, including the human and several plants, and we outline the mapping strategies that have been used.

Chromosome Mapping↗
PubMed2002

A preliminary linkage map of the tick, Ixodes scapularis.

A linkage map of the Ixodes scapularis genome was constructed based upon segregation amongst 127 loci. These included 84 random amplified polymorphic DNA (RAPD) markers, 32 Sequence-Tagged RAPD (STAR) markers, 5 cDNAs, and 5 microsatellites in 232 F1 intercross progeny from a single, field-collected P1 female. A preliminary linkage map of 616 cM was generated across 14 linkage groups with one marker every 10.8 cM. Assuming a genome size of approximately 10(9) bp, the relationship of physical to genetic distance is approximately 300 kb/cM in the I. scapularis genome.

Animals↗
PubMed2002

Molecular linkage maps of the Populus genome.

We report molecular genetic linkage maps for an interspecific hybrid population of Populus, a model system in forest-tree biology. The hybrids were produced by crosses between P. deltoides (mother) and P. euramericana (father), which is a natural hybrid of P. deltoides (grandmother) and P. nigra (grandfather). Linkage analysis from 93 of the 450 backcross progeny grown in the field for 15 years was performed using random amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), and inter-simple sequence repeats (ISSRs). Of a total of 839 polymorphic markers identified, 560 (67%) were testcross markers heterozygous in one parent but null in the other (segregating 1:1), 206 (25%) were intercross dominant markers heterozygous in both parents (segregating 3:1), and the remaining 73 (9%) were 19 non-parental RAPD markers (segregating 1:1) and 54 codominant AFLP markers (segregating 1:1:1:1). A mixed set of the testcross markers, non-parental RAPD markers, and codominant AFLP markers was used to construct two linkage maps, one based on the P. deltoides (D) genome and the other based on P. euramericana (E). The two maps showed nearly complete coverage of the genome, spanning 3801 and 3452 cM, respectively. The availability of non-parental RAPD and codominant AFLP markers as orthologous genes allowed for a direct comparison of the rate of meiotic recombination between the two different parental species. Generally, the rate of meiotic recombination was greater for males than females in our interspecific poplar hybrids. The confounded effect of sexes and species causes the mean recombination distance of orthologous markers to be 11% longer for the father (P. euramericana; interspecific hybrid) than for the mother (P. deltoides; pure species). The linkage maps constructed and the interspecific poplar hybrid population in which clonal replicates for individual genotypes are available present a comprehensive foundation for future genomic studies and quantitative trait locus (QTL) identification.

Chi-Square Distribution↗
PubMedDate not supplied

Phytophthora sojae avirulence genes, RAPD, and RFLP markers used to construct a detailed genetic linkage map.

Two crosses between different races of Phytophthora sojae were established using one race as a common parent in both crosses. F2 populations comprising over 200 individuals were generated for each cross. A subset of 53 F2 individuals from each cross was selected at random for genetic analysis of virulence/avirulence and molecular markers, and finally the construction of a detailed genetic linkage map. The linkage map developed for P. sojae is based on a total of 257 markers (22 RFLP, 228 RAPD, and 7 avirulence genes). The linkage map comprises 10 major and 12 minor linkage groups covering a total of 830.5 cM. Close linkage was observed between Avr4 and Avr6 (0.0 cM), Avr1b and Avr1k (0.0 cM), and Avr3a and Avr5 (4.6 cM). Coupling phase linkage of RFLP and RAPD markers to all seven avirulence genes was identified at the minimum and maximum distances of 0.0 and 14.7 cM, respectively.

Chromosome Mapping↗
PubMed2004

[Constructing genetic linkage maps in Chinese Fir using F1 progeny].

A new strategy was proposed for constructing linkage maps for 1:1 segregation molecular markers in Chinese fir. Linkage phase and recombination ratio for any two loci can be inferred and estimated. For the best order in a linkage group, the Hidden Markov Chain Model was used for multilocus linkage analysis. The mapping method proposed here was more effective than the 'pseudo-testcross' method commonly used in forest trees. In this paper,with the AFLP marker data obtained from the F1 progeny of 'Jurong 0' (female) x 'Rouye' (male), the genetic linkage maps of the Chinese fir clones, 'Jurong' and 'Rouye', were reconstructed based on the new mapping method. In the genetic linkage map of "Jurong 0", 101 markers were distributed in 11 linkage groups with an average distance of 22.6 cM and a total length of 2 282.6 cM. There were as many as 17 markers and as few as 5 markers in single linkage groups of the map. In the genetic linkage map of 'Rouye', 94 markers were distributed in the 11 linkage groups with an average distance of 27.3 cM and a total length of 2 565.8 cM. There were as many as 16 markers and as few as 4 markers in single linkage groups of the map. Compared with the 'pseudo- testcross' method, the two maps increased 26 markers and 28 markers, respectively, and totally 54 markers were added. The two maps contained 195 AFLP markers and each spanned more than 2 000 cM, almost covering the whole genome of Chinese fir. Therefore, the resolutions of linkage maps of Chinese fir 'Jurong 0' and 'Rouye' were improved with the new mapping method, and the maps provide the framework for further genetic analysis.

Chromosome Mapping↗
PubMed1993

A genetic linkage map with 29 loci spanning human chromosome 13q.

A genetic linkage map for the long arm of human chromosome 13 contains 29 loci derived from 38 probe and enzyme combinations and two protein polymorphisms. Thirteen loci form a continuous linkage map of 106 cM in males and 230 cM in females; each was placed on the map with support of at least 1000:1 against alternative orders. On a sex-combined basis, the mean distance between markers is less than 13 cM. The order of loci on the genetic map agrees with physical localization data that show that together these 13 loci cover 13q13 to 13q34. This map was used to regionally localize the 16 remaining loci. The linkage maps reported here should prove to be useful to investigators mapping disease genes and other genetic markers on human chromosome 13.

Alleles↗
PubMed1996

The linkage map of sheep Chromosome 6 compared with orthologous regions in other species.

The genetic linkage map of sheep Chromosome (Chr) 6 has been extended to include 35 loci with the addition of 11 RFLP and 12 microsatellite loci. The sex-averaged linkage map now spans 154 cM from phosphodiesterase cyclic GMP beta polypeptide (PDE6B) to OarCP125, an anonymous sheep microsatellite. The male and female map lengths, at 180 cM and 132 cM respectively, did not differ significantly. The physical assignment of PDE6B to Chr 6q33-qter orientates the linkage map on sheep Chr 6 with PDE6B near the telomere and OarCP125 towards the centromere. The order and genetic distances between loci are similar for the sheep Chr 6 and cattle Chr 6 maps, except for the position of the casein genes. The sheep Chr 6 linkage map is also comparable to portions of human Chr 4, mouse Chrs 5 and 3, and pig Chr 8. The synteny between sheep Chr 6 and human Chr 4 has been extended from PDE6B (4p16.3) to epidermal growth factor (EGF, 4q25-q27). However, a region from platelet-derived growth factor receptor alpha polypeptide (PDGFRA) to bone morphogenetic protein 3 (BMP3), which spans 19 cM on sheep Chr 6, appears to be inverted with respect to the human and mouse loci. Other differences in the gene order between sheep, pig, and mouse suggest more complex rearrangements.

Animals↗
PubMed1997

Linkage map of phenotype and RFLP markers in rice.

The results from linkage mapping activities at Kyushu University during the last 10 years are summarized in this paper. The present paper concisely reveals present situation on linkage map of phenotype markers, the integration linkage map of phenotype and RFLP markers and the genetic stocks available. Some of the problems in this field, in addition, are pointed out and discussed.

Genes, Plant↗
PubMed2005

Microsatellite-based high density linkage map in oil palm (Elaeis guineensis Jacq.).

A microsatellite-based high-density linkage map for oil palm (Elaeis guinensis Jacq.) was constructed from a cross between two heterozygous parents, a tenera palm from the La Me population (LM2T) and a dura palm from the Deli population (DA10D). A set of 390 simple sequence repeat (SSR) markers was developed in oil palm from microsatellite-enriched libraries and evaluated for polymorphism along with 21 coconut SSRs. A dense and genome-wide microsatellite framework as well as saturating amplified fragments length polymorphisms (AFLPs) allowed the construction of a linkage map consisting of 255 microsatellites, 688 AFLPs and the locus of the Sh gene, which controls the presence or absence of a shell in the oil palm fruit. An AFLP marker E-Agg/M-CAA132 was mapped at 4.7 cM from the Sh locus. The 944 genetic markers were distributed on 16 linkage groups (LGs) and covered 1,743 cM. Our linkage map is the first in oil palm to have 16 independent linkage groups corresponding to the plant's 16 homologous chromosome pairs. It is also the only high-density linkage map with as many microsatellite markers in an Arecaceae species and represents an important step towards quantitative trait loci analysis and physical mapping in the E. guineensis species.

Arecaceae↗
PubMed2002

Genetic linkage maps of two apricot cultivars ( Prunus armeniaca L.), and mapping of PPV (sharka) resistance.

Genetic linkage maps for two apricot cultivars have been constructed using AFLP, RAPD, RFLP and SSR markers in 81 F1 individuals from the cross 'Goldrich' x 'Valenciano'. This family segregated for resistance to 'plum pox virus' (PPV), the most-important virus affecting Prunus species. Of the 160 RAPD arbitrary primers screened a total of 44 were selected. Sixty one polymorphic RAPD markers were scored on the mapping population: 30 heterozygous in 'Goldrich', 19 heterozygous in 'Valenciano', segregating 1:1, and 12 markers heterozygous in both parents, segregating 3:1. A total of 33 and 19 RAPD markers were mapped on the 'Goldrich' and 'Valenciano' maps respectively. Forteen primer combinations were used for AFLPs and all of them detected polymorphism. Ninety five markers segregating 1:1 were identified, of which 62 were heterozygous in the female parent 'Goldrich' and 33 in the male parent 'Valenciano'. Forty five markers were present in both parents and segregated 3:1. A total of 82 and 48 AFLP markers were mapped on the 'Goldrich' and 'Valenciano' maps. Twelve RFLPs probes were screened in the population, resulting in five loci segregating in the family, one locus heterozygous for 'Valenciano' and four heterozygous for both, segregating 1:2:1. Of the 45 SSRs screened 17 segregated in the mapping family, resulting in seven loci heterozygous for the maternal parent and ten heterozygous for both, segregating 1:2:1 or 1:1:1:1. A total of 16 and 13 co-dominant markers were mapped in the female and male parent maps respectively. A total of 132 markers were placed into eight linkage groups on the 'Goldrich' map, defining 511 cM of the total map-length. The average distance between adjacent markers was 3.9 cM. A total of 80 markers were placed into seven linkage groups on the 'Valenciano' map, defining 467.2 cM of the total map-distance, with an average interval of 5.8 cM between adjacent markers. Thirty six marker loci heterozygous in both parents revealed straightforward homologies between five linkage groups in both maps. The sharka resistance trait mapped on linkage group 2. The region containing sharka resistance is flanked by two co-dominant markers that will be used for targeted SSR development employing a recently constructed complete apricot BAC library. SSRs tightly linked to sharka resistance will facilitate MAS in breeding for resistance in apricot.

Journal Article↗