Length Of Linkage Groups Research Articles

Linkage map for chromosome-level genome anchoring and genome-wide association study for resistance to Aeromonas hydrophila in Colossoma macropomum

Tambaqui (Colossoma macropomum) is the most important neotropical fish in freshwater aquaculture in South America. Disease outbreaks caused by the bacterium Aeromonas hydrophila have resulted in significant losses to tambaqui production. Selective breeding using genomic information is a powerful strategy to improve disease resistance in fish species. The first step to incorporating genomic information in breeding programs is determining the number of loci or genes that can affect targeted traits. In this study, we developed a dense linkage map for chromosome-level scaffolding and investigated the genetic architecture of resistance to A. hydrophila in tambaqui in a genome-wide association study (GWAS). The single nucleotide polymorphism (SNP) genotypes from 275 animals belonging to 18 full sib-families were obtained using the novel genotyping platform Axiom 30 K SerraSNP array for tambaqui. The genomic analysis revealed low to moderate heritability values for both resistance trait definitions: h2 = 0.26 (0.10) for test survival and h2 = 0.27 (± 0.10) for time to death. A dense linkage map was developed for tambaqui using the genotype data, resulting in 17,374 SNPs distributed across 27 linkage groups. The length of linkage groups varied from 124 (LG1) to 50 (LG14) cM, with a total integrated map length of 2298.91 cM. The female map was longer than the male map. GWAS analysis identified several putative QTLs associated with A. hydrophila resistance, distributed in six linkage groups. Several candidate genes related to immune response were located close to the putative QTLs, such as irf4a, ripk1l, il20ra, c8a, c8b, ube3c, and ccr9a. This study represents the first application of a 30 K SNP array to build a dense linkage map anchoring 27 megascaffolds (chromosomes) of the genome, and to identify genetic variants associated with A. hydrophila resistance in tambaqui.

Genetic mapping and QTL analysis of important traits based on single nucleotide polymorphisms in Acacia hybrid population

Acacia hybrids are fast-growing with a great potential to grow on marginal lands. Developing a Marker Assisted Selection (MAS) program requires linkage and QTL maps. A. auriculiformis and A. mangium hybrid populations were developed based on contrasting traits of wood density and fibre length. In this study, only the wood density population could be used due to the availability of a high number of polymorphic markers. A linkage map was constructed comprising 362 single nucleotide polymorphism (SNP) loci spanning across 13 linkage groups. The map covered 1335.12 cM of linkage map has an average marker distance of 3.69 cM. The genetic length of linkage groups (LGs) ranged from 20.8 cM (LG13) to 162.8 cM (LG1), with an average of 3.69 cM. The observed genome coverage in the present study was 94.85. In total, 18 QTLs were identified for plant height, 9 for biomass, 13 for DBH, and 11 for wood density. Candidate genes were proposed through comparative marker analysis and fine mapping of identified QTLs would facilitate the identification of genes and applying marker-assisted selection breeding for the selected traits in Acacia.

Molecular mapping and identification of QTLs responsible for charcoal rot resistance in Castor (Ricinus communis L.)

Charcoal rot caused by Macrophomina phaseolina in castor is one of the major pathogenic determinants for extreme yield loss. The charcoal rot resistance trait is complex and controlled by quantitative trait locis (QTLs). This study was aimed to develop linkage map and to identify novel QTLs associated with charcoal rot resistance in castor. A mapping population (F2:3) derived from the cross between two castor inbred lines JI 357 (Resistant genotype) and SKI 338 (Susceptible genotype) was developed and screened in the sick plot using randomised block design. After screening 920 (520 RAPD, 100 ISSR, 300 SSR) primers among the parental lines, 336 polymorphic markers were identified to be used for genotyping the mapping population to develop genetic linkage map. The genetic map consisting of 10 linkage group covering a total map length of 1833.4centimorgan (cM) with average marker interval of 6.93cM was developed. The length of linkage groups varied from 121.5cM for linkage group 10 (C10) to 278.7cM for linkage group 9 (C9). The average marker interval was maximum in C3 (8.23cM) while it was lowest in C10 (5.78cM). Analysing genotypic data along with phenotypic data collected from mapping population against charcoal rot in sick plot, identified three novel QTLs explaining 11.3–71.2% of phenotypic variation. One major QTL with LOD score of 6.5 was identified on linkage group 2 explaining 71.2% of phenotypic variation, is a most promising QTL for molecular breeding. This is the first study reporting novel QTLs for charcoal rot resistance in castor and thus future studies will be conducted to refine these QTLs.

An Integrated Genetic Linkage Map from Three F2 Populations of Cultivated Peanut( Arachis hypogaea L.)

The genetic linkage map is important for peanut molecular breeding. Construction of integrating genetic linkage map using multiple populations is an effective approach to increase the marker density of map. Three maps were constructed with three F2 populations, respectively in the present study. Based on anchored SSR markers in the three maps, we constructed a new map with 792 SSR loci and total map distance of 2079.50 cM (the average distance is 2.63 cM). The length of linkage groups varied from 59.10 to 175.80 cM, and the number of markers was from 20 to 66 in the integrated linkages groups. Comparing the intervals of QTLs linked to the pod size and seed size in the three F2 populations with the markers in the integrated linkage groups, all the QTLs linked to the pod size and seed size could be found in the integrated map. Some intervals of QTLs had more markers in the integrated map than in the F2 linkage groups in the present study. The markers in the intervals of QTLs of the integrated map could be used for fine mapping.

Construction of a genetic linkage map in Lilium using a RIL mapping population based on SRAP marker

A genetic linkage map of lily was constructed using RILs (recombinant inbred lines) population of 180 individuals. This mapping population was developed by crossing Raizan No.1 (Formolongo) and Gelria (Longiflomm) cultivars through single-seed descent (SSD). SRAPs were generated by using restriction enzymes EcoRI in combination with either MseI. The resulting products were separated by electrophoresis on 6% denaturing polyacrylamide gel and visualized by silver staining. The segregation of each marker and linkage analysis was done using the program Mapmaker3.0. With 50 primer pairs, a total of 189 parental polymorphic bands were detected and 78 were used for mapping. The total map length was 2,135.5 cM consisted of 16 linkage groups. The number of markers in the linkage groups varied from 1 to 12. The length of linkage groups was range from 11.2 cM to 425.9 cM and mean marker interval distance range from 9.4 cM to 345.4 cM individually. The mean marker interval distance between markers was 27.4 cM. The map developed in the present study was the first sequence-related amplified polymorphism markers map of lily constructed with recombinant inbred lines, it could be used for genetic mapping and molecular marker assisted breeding and quantitative trait locus mapping of Lilium.

Construction of a genetic map of sunflower using a population of recombinant inbred lines (RILs)

A genetic linkage map of sunflower was constructed by combined applying the SSR and AFLP markers using 187 F5:6 individuals of recombinant inbred lines (RILs) which derived from the cross between Helianthus annuus K55 and Helianthus annuus K58 through single-seed descent (SSD). Using 78 pairs of SSR primers and 48 pairs of AFLP primer, 341 and 1119 bands were amplified, respectively. Among these 1460 bands, 557 bands (39.52%) were polymorphic, including 184 bands by SSR markers and 393 bands by AFLP markers. In the group of these polymorphic bands, 84 bands from SSR markers and 108 bands from AFLP markers showed the genetic distortion (P = 0.05). A total of 192 segregation distortion markers were obtained in this study. By using the JoinMap 4.0 software to do the linkage analysis, a genetic linkage map was established with length of 2759.4 cM, consisted of 17 linkage groups, and comprised of 495 polymorphic molecular markers including 170 segregation distortion markers. The mean marker interval distance is 5.57 cM between markers. In addition, the number of markers in the linkage groups varied from 5 to 72, and the length of linkage groups were from 68.88 cM to 250.17 cM. The genetic map developed in the present study could be used for QTL mapping and gene cloning of sunflower important genes.

A second-generation genetic linkage map for bighead carp (Aristichthys nobilis) based on microsatellite markers.

Bighead carp (Aristichthys nobilis) is an important aquaculture fish worldwide. Genetic linkage maps for the species were previously reported, but map resolution remained to be improved. In this study, a second-generation genetic linkage map was constructed for bighead carp through a pseudo-testcross strategy using interspecific hybrids between bighead carp and silver carp. Of the 754 microsatellites genotyped in two interspecific mapping families (with 77 progenies for each family), 659 markers were assigned to 24 linkage groups, which were equal to the chromosome numbers of the haploid genome. The consensus map spanned 1917.3cM covering 92.8% of the estimated bighead carp genome with an average marker interval of 2.9cM. The length of linkage groups ranged from 52.2 to 133.5cM with an average of 79.9cM. The number of markers per linkage group varied from 11 to 55 with an average of 27.5 per linkage group. Normality tests on interval distances of the map showed a non-normal marker distribution; however, significant correlation was found between the length of linkage group and the number of markers below the 0.01 significance level (two-tailed). The length of the female map was 1.12 times that of the male map, and the average recombination ratio of female to male was 1.10:1. Visual inspection showed that distorted markers gathered in some linkage groups and in certain regions of the male and female maps. This well-defined genetic linkage map will provide a basic framework for further genome mapping of quantitative traits, comparative mapping and marker-assisted breeding in bighead carp.

Comparison of Two Genetic Maps of Soybean Constructed by RIL Populations Derived from Combinations of Peking×7605 under Two Ecological Sites

Molecular linkage maps provide a powerful tool for the analysis of plant genome structure and function, and it is im-portant to determine the effect of ecological environment on soybean genetic map construction. Two soybean recombinant inbred line (RIL) populations named "JN(RN)P7" and "NJ(RN)P7" were tested in this study, which were derived from Peking × 7605 at Jinan and Nanjing, respectively. One hundred and forty-five SSR markers and one morphologic marker (BSC) which had poly-morphism between parents were screened out to construct two genetic linkage maps using JoinMap 4.0 software. And we obtained two soybean genetic maps, which contained 27 and 25 of the linkage groups, respectively. The total length of two genetic maps was 1 574.80 and 1 682.50 cM, and the average distance between markers was 13.58 and 15.72 cM, respectively. The length of linkage group varied from 17.30 to 127.40 cM for JN(RN)P7, and from 20.10 to 137.50 cM for NJ(RN)P7. Both genetic maps were homologous with the public genetic map. The two maps constructed in this study were mostly coincident with each other, while certain differences were observed too, which indicated that there were some genetic structure differences between the two populations caused by the selection effect in various environments.

Genetic linkage mapping and genetic analysis of QTL related to eye cross and eye diameter in common carp (Cyprinus carpio L.) using microsatellites and SNPs

A group of 68 F1 hybrid common carp was used to construct a linkage map using JoinMap4.0 software. A total of 507 microsatellite and SNP markers isolated from genomic library (186 SSR and 321 SNP markers) were assigned to construct the genetic map, comprising 62 linkage groups. The total length of the linkage map for the common carp is 2805.85cM with an average linkage group length of 6.31cM. Both eye diameter and eye cross were located on the genetic map. Eight QTL were found to be associated with eye diameter, explaining 16.60–36.70% of the total phenotypic variation. Eleven QTL were found to be related to eye cross, explaining 13.6–31.6% of the total phenotypic variation. Five major QTL for eye diameter and nine major QTL for eye cross explained the highest fraction of the phenotypic variation. The relationship of eye cross and eye diameter with other commercial traits and QTL linkage group analysis suggests that eye diameter and eye cross might be used to assist in indirect selection for body weight and aggregate breeding could achieve multiple effects. These findings have implications for future genetic studies and breeding of the common carp.

Factors Affected BC1F1 Size for Development of Genome-Wide Introgression Lines

Introgression lines are important genetic materials for genetics study and breeding. Development of those lines involves cross and backcross processes between recipient and donor parents. The population size of BC1F1 is a critical parameter for fully covering donor genome and successfully obtaining desired introgression lines. However, the minimum sufficient number of BC1F1 plants is unknown for each species and cannot be obtained experimentally. A computer program was developed by simulating the recombination process during meiosis to define the ideal BC1F1 population size. The reliability of the program was confirmed by mathematics and experimental data. Three factors including linkage group number, linkage group length, and gene density were analyzed, and all of them had positive relation with the size of BC1F1 population. The population size increased from 6.06 to 9.49 when the linkage number increased from 5 to 40. The population size was 7.14 when the linkage group length was 80 cM, while it became 8.64 when the length was 200 cM. The population size was 7.65 with the density of 20 cM per gene and 8.22 with 10 cM per gene. The BC1F1 population sizes of rice (Oryza sativa L.), wheat (Triticum aestivum L.), maize (Zea mays L.), and soybean (Glycine max L. Merr.) were predicted to be 12, 13, 14–15, and 13, respectively, by the program with 95% confidential level.

Construction of a genetic linkage map for silver carp (Hypophthalmichthys molitrix)

For silver carp (Hypophthalmichthys molitrix), a combined microsatellite (or simple sequence repeat) and amplified fragment length polymorphism (AFLP) sex average linkage map was constructed. A total of 483 markers (245 microsatellites and 238 AFLPs) were assigned to 33 linkage groups. The map spanned 1352.2 cM, covering 86.4% of the estimated genome size of silver carp. The maximum and average spaces between 420 loci were 21.5 cM and 3.2 cM, respectively. The length of linkage groups ranged from 3.6 cM to 98.5 cM with an average of 41.0 cM. The number of markers per group varied from 2 to 44 with an average of 14.6. The AFLP markers significantly improved the integrity of microsatellite-based linkage groups and increased the genome coverage and marker evenness. A genome-wide recombination suppression was observed in male. In an extreme case, six microsatellites co-segregated in male, but spanned a 45.1 cM region in female.

A linkage map of common carp (Cyprinus carpio) based on AFLP and microsatellite markers

Common carp (Cyprinus carpio) is an important fish for aquaculture, but genomics of this species is still in its infancy. In this study, a linkage map of common carp based on Amplified Fragment Length Polymorphism (AFLP) and microsatellite (SSR) markers has been generated using gynogenetic haploids. Of 926 markers genotyped, 151 (149 AFLPs, two SSRs) were distorted and eliminated from the linkage analyses. A total of 699 AFLP and 20 microsatellite (SSR) markers were assigned to the map, which comprised 64 linkage groups and covered 5506.9 cM Kosambi, with an average interval distance of 7.66 cM Kosambi. The normality tests on interval map distances showed a non-normal marker distribution. Visual inspection of the map distance distribution histogram showed a cluster of interval map distances on the left side of the chart, which suggested the occurrence of AFLP marker clusters. On the other hand, the lack of an obvious cluster on the right side showed that there were a few big gaps which need more markers to bridge. The correlation analysis showed a highly significant relatedness between the length of linkage group and the number of markers, indicating that the AFLP markers in this map were randomly distributed among different linkage groups. This study is helpful for research into the common carp genome and for further studies of genetics and marker-assisted breeding in this species.

THE MICROSATELLITE (SSR)/AFLP REFERENCE LINKAGE MAP OF GUAVA

An integrated parental linkage map of guava (Psidium guajava L., 2n = 22) based on AFLP and SSR markers has been constructed for the mapping population MP1 derived from a cross between two heterozygous guava cultivars (Enana x N6). A total of 1103 segregating AFLP markers obtained from 119 AFLP primer combinations were produced for linkage mapping. In addition, 171 SSR maker loci were analysed which generated 258 allelic fragments. In total 1364 AFLP and SSR markers were available for linkage mapping. The integrated linkage map of MP1 contains 578 markers (452 AFLPs, 126 SSRs) distributed on 11 linkage groups corresponding to the 11 chromosomes of the haploid guava genome. This map has a length of 2179 cM and an average linkage group length of 198 cM. In addition, a total of 126 so-called RF0 markers and 146 so-called associated markers were determined. The current MP1 map will be completed by the integration of the individual maps derived from other available guava mapping populations. This represents a decisive step towards a saturated genetic reference map of P. guajava in support of accelerated breeding in guava by marker-assisted selection.

Construction of Molecular Genetic Map and QTL Analysis of Fiber Quality in Cotton

Cotton is a leading textile fiber crop in the world and a source of secondary products such as oil, live-stock feed (cot-ton seed cake) and cellulose. The improvement of cotton fiber quality is becoming extremely important with the innovation of spinning technology. A genetic map is necessary not only for the reliable detection, mapping and estimation of gene effects of important agronomic traits, but also for further research on the structure, organization, evolution and function of cotton genome. In the present study, simple sequence repeats (SSRs) and amplified fragment length polymorphism (AFLP) were used to assay an F2 population from a cross between CRI8 (Gossypium hirsutum L.) and Pima 90-53 (Gossypium barbadense L.). Two hundred and fourteen F2 plants were used for map construction using 110 SSRs and 65 AFLPs. This map included 175 markers distributing on 42 linkage groups, covering 2 030 cM, accounting for 40.6% of the cotton genome, and with an average distance of 11.6 cM be-tween two markers. The length of linkage groups ranged from 4.5 to 147.3 cM and the markers on the groups ranged from 2 to 22. The linkage map was located on 10 chromosomes, which were Chr.4, Chr.8, Chr.9, Chr.10, Chr.12, Chr.14, Chr.15, Chr.18, Chr.21, and Chr.25. Based on composite interval mapping, five QTLs were identified for fiber length, distributing on Chr.21, Chr.15, LG2, and LG12, explaining 10.2–35.8% of the fiber length variance. Four QTLs were identified for length uniformity, distributing on Chr.21, LG9, LG18, and LG12, explaining 12.6–36.6% of the fiber length uniformity variance. Seven QTLs were identified for micronaire, distributing on Chr.9, LG1, LG9, LG20, and LG12, explaining 11.5–26.1% of the fiber micronaire variance. Seven QTLs were identified for strength, distributing on Chr.21, Chr.12, Chr.8, LG1, LG4, and LG10, explaining 16.5–52.8% of the fiber strength variance. Two QTLs were identified for fiber elongation, distributing on Chr.9 and Chr.21, explaining 18.1% and 27.1% of the fiber elongation variance. Assembled section of QTLs existed in LG9, LG12, and Chr.21. The present map and QTL analysis may provide a useful tool for breeders to transfer desirable traits from G. barbadense to the mainly cultivated species, G. hirsutum.

A microsatellite (SSR) based linkage map of Brassica rapa

In the present study we describe the construction of a genetic linkage map for the Brassica rapa (AA) genome that will act as a key resource in undertaking future structural and functional genomic studies in B. rapa. A F(2) mapping population consisting of 48 F(2) individual plants developed following hybridization of 2 inbred lines Bathari mandi and IC 331817 was used to construct the map. The map comprises 53 SSR markers derived from 3 different public domain resources. Nine linkage groups along with a small subgroup were identified and designated as R(1)-R(9) through alignment and orientation using SSR markers in common with existing B. rapa reference linkage maps. The total length of the genetic linkage map was 354.6 cm with an average interval of 6.6 cm between adjacent loci. The length of linkage groups ranged from 28.0 cm to 44.2 cm for R(6) and R(1A), respectively. The number variability of markers in the 9 linkage groups ranged from 3 for R(6) to 10 for R(1). Of the 53 SSR markers assigned to the linkage groups, only 5 (9.4%) showed deviation from the expected segregation ratio. The development of this map is vital to the genome integration and genetic information and will enable the international research community to share resources and data for the improvement of B. rapa and other cultivated Brassica species.

A genetic linkage map of Physocarpus, a member of the Spiraeoideae (Rosaceae), based on RAPD, AFLP, RGA, SSR and gene specific markers

Abstract Physocarpus opulifolius is a deciduous shrub native to North America belonging to the Spiraeoideae subfamily of the Rosaceae. The cultivars ‘Luteus’ and ‘Diabolo’ are grown in gardens for their ornamental foliage, golden and purple respectively. We developed a linkage map of P. opulifolius with a view to detecting markers for the leaf colour genes, which are under major gene control. A total of 162 molecular markers (128 RAPDs, 27 AFLPs, three RGA, three STS markers and one SSR) and the leaf colour genes Pur and Aur were scored in the Physocarpus progeny and used to create a linkage map covering 586.1 cM over nine linkage groups. There was an average of 18.2 markers per linkage group and a mean linkage group length of 65.1 cM. Both leaf colour genes were mapped. This is the first reported linkage map of a member of the Spireaeoideae and the mapping of a small number of transferable markers has demonstrated its utility to comparative mapping, which will complement existing comparative mapping efforts in other rosaceous subfamilies.

Construction of a molecular map for melon (Cucumis melo L.) based on SRAP

A molecular map of melon (Cucumis melo L.) was constructed with SRAP (Sequence-Related Amplified Polymorphism) markers using a population consisting of 114 F2 individuals derived from the cross of 4G21 (C. melo var. chinensis) and 3A832 (C. melo var. saccherinus). Twenty-nine primer pairs were used and 187 polymorphic loci were produced. The map consists of 12 linkage groups that include 152 genetic markers and cover 2077.1 cM with an average genetic distance of 13.67 cM. Every linkage group has 6–32 genetic markers with average genetic distance of 9.72–19.19 cM. The length of linkage group is 85.3–496.1 cM.

The reference genetic linkage map for the multinational Brassica rapa genome sequencing project

We describe the construction of a reference genetic linkage map for the Brassica A genome, which will form the backbone for anchoring sequence contigs for the Multinational Brassica rapa Genome Sequencing Project. Seventy-eight doubled haploid lines derived from anther culture of the F(1) of a cross between two diverse Chinese cabbage (B. rapa ssp. pekinensis) inbred lines, 'Chiifu-401-42' (C) and 'Kenshin-402-43' (K) were used to construct the map. The map comprises a total of 556 markers, including 278 AFLP, 235 SSR, 25 RAPD and 18 ESTP, STS and CAPS markers. Ten linkage groups were identified and designated as R1-R10 through alignment and orientation using SSR markers in common with existing B. napus reference linkage maps. The total length of the linkage map was 1,182 cM with an average interval of 2.83 cM between adjacent loci. The length of linkage groups ranged from 81 to 161 cM for R04 and R06, respectively. The use of 235 SSR markers allowed us to align the A-genome chromosomes of B. napus with those of B. rapa ssp. pekinensis. The development of this map is vital to the integration of genome sequence and genetic information and will enable the international research community to share resources and data for the improvement of B. rapa and other cultivated Brassica species.

Mapping of A1 conferring resistance to the aphid Amphorophora idaei and dw (dwarfing habit) in red raspberry (Rubus idaeus L.) using AFLP and microsatellite markers

BackgroundRaspberry breeding programmes worldwide aim to produce improved cultivars to satisfy market demands and within these programmes there are many targets, including increased fruit quality, yield and season, and improved pest and disease resistance and plant habit. The large raspberry aphid, Amphorophora idaei, transmits four viruses and vector resistance is an objective in raspberry breeding. The development of molecular tools that discriminate between aphid resistance genes from different sources will allow the pyramiding of such genes and the development of raspberry varieties with superior pest resistance. We have raised a red raspberry (Rubus idaeus) F1 progeny from the cross 'Malling Jewel' × 'Malling Orion' (MJ × MO), which segregates for resistance to biotype 1 of the aphid Amphorophora idaei and for a second phenotypic trait, dwarf habit. These traits are controlled by single genes, denoted (A1) and (dw) respectively.ResultsThe progeny of 94 seedlings was scored for the segregation of 95 AFLP and 22 SSR markers and a linkage map was constructed that covers a total genetic distance of 505 cM over seven linkage groups. The average linkage group length was 72.2 cM and there was an average of 17 markers per linkage group, of which at least two were codominant SSRs, allowing comparisons with previously published maps of raspberry. The two phenotypic traits, A1 and dw, mapped to linkage groups 3 and 6 respectively.ConclusionThe mapping of A1 will facilitate the discrimination of resistance genes from different sources and the pyramiding of aphid resistance genes in new raspberry cultivars; the mapping of dw will allow further investigations into the genetics of dwarfing habit in Rubus.

Construction and analysis of an AFLP molecular linkage map of the silkworm (Bombyx mori)

AbstractAn amplification fragment length polymorphism (AFLP) molecular linkage map with a relatively high density for location of quantitative trait loci (QTLs) controlling the quantitative traits of silkworm (Bombyx mori) cocoons, was constructed using 91 individuals of the F2generation. Among the 692 effective loci, 550 were allocated to subgroups a and b, of which 21 linkage groups in subgroup a had 233 molecular markers and 28 linkage groups in subgroup b had 317 markers. The number of markers on each linkage group in subgroups a and b ranged from 4 to 43 and 3 to 35, respectively. The total length of linkage groups for subgroup a was 1868.10 cM, and 2677.50 cM for subgroup b. The length of linkage group varied from 22.3 to 424.3 cM in subgroup a and from 2.4 to 366.5 cM in subgroup b. The average variation in the distance between markers was 3.39–17.43 cM in subgroup a and 0.8–26.96 cM in subgroup b. The average distance between the markers was 8.81 cM in subgroup a and 9.26 cM in subgroup b. There were 14 linkage groups, with an average distance below 10 cM, in subgroup a and 18 linkage groups in subgroup b. There were seven linkage groups with an average distance between 10 and 20 cM in subgroup a and ten linkage groups in subgroup b. Each linkage group in subgroup a had 11.1 loci on average, while there were 11.31 loci on each linkage group on average in subgroup b. The mean length for linkage groups in subgroups a and b was 89 and 95.6 cM, respectively. The total average length for both a and b subgroups was 2272.8, and 9.06 cM for the average marker distance, fulfilling the basic known requirements for locating QTLs.