An apricot (Prunus armeniaca L.) F2 progeny linkage map based on SSR and AFLP markers,mapping plum pox virus resistance and self-incompatibility traits

A genetic linkage map of apricot ( Prunus armeniaca L.) was constructed using AFLP and SSR markers. The map is based on an F(2) population (76 individuals) derived from self-pollination of an F(1) individual ('Lito') originated from a cross between 'Stark Early Orange' and 'Tyrinthos'. This family, designated as 'Lito' x 'Lito', segregated for two important agronomical traits: plum pox virus resistance (PPV) and self-incompatibility. A total of 211 markers (180 AFLPs, 29 SSRs and two agronomic traits) were assigned to 11 linkage groups covering 602 cM of the apricot genome. The average distance (cM/marker) between adjacent markers is 3.84 cM. The PPV resistance trait was mapped on linkage group G1 and the self-incompatibility trait was mapped on linkage group G6. Twenty two loci held in common with other Prunus maps allowed us to compare and establish homologies among the respective linkage groups.     

An expanded genetic linkage map of Prunus based on an interspecific cross between almond and peach.

The genetic linkage map of Prunus constructed earlier and based on an interspecific F2 population resulting from a cross between almond (Prunus dulcis D.A. Webb) and peach (Prunus persica L. Batsch) was extended to include 8 isozyme loci, 102 peach mesocarp cDNAs, 11 plum genomic clones, 19 almond genomic clones, 7 resistance gene analogs (RGAs), 1 RGA-related sequence marker, 4 morphological trait loci, 3 genes with known function, 4 simple sequence repeat (SSR) loci, 1 RAPD, and 1 cleaved amplified polymorphic sequence (CAP) marker. This map contains 161 markers placed in eight linkage groups that correspond to the basic chromosome number of the genus (x = n = 8) with a map distance of 1144 centimorgans (cM) and an average marker density of 6.8 cM. Four more trait loci (Y, Pcp, D, and SK) and one isozyme locus (Mdh1) were assigned to linkage groups based on known associations with linked markers. The linkage group identification numbers correspond to those for maps published by the Arús group in Spain and the Dirlewanger group in France. Forty-five percent of the loci showed segregation distortion most likely owing to the interspecific nature of the cross and mating system differences between almond (obligate outcrosser) and peach (selfer). The Cat1 locus, known to be linked to the D locus controlling fruit acidity, was mapped to linkage group 5. A gene or genes controlling polycarpel fruit development was placed on linkage group 3, and control of senesced leaf color (in late fall season) (LFCLR) was mapped to linkage group 1 at a putative location similar to where the Y locus has also been placed.     

Combined RAPD and RFLP molecular linkage map of asparagus.

Two linkage maps of asparagus (Asparagus officinalis L.) were constructed using a double pseudotestcross mapping strategy with restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), and allozymes as markers in a population generated from crossing MW25 x A19, two heterozygous parents. All data were inverted and combined with the natural data to detect linkages in repulsion phase. Two sets of data, one for each parent, were formed according to the inheritance patterns of the markers. The maternal MW25 map has a total of 163 marker loci placed in 13 linkage groups covering 1281 cM, with an average and a maximum distance between adjacent loci of 7.9 and 29 cM, respectively. The paternal A19 map has 183 marker loci covering 1324 cM in 9 linkage groups, with an average and a maximum distance between two adjacent loci of 7.7 and 29 cM, respectively. Six multiallelic RFLPs segregating in the pattern a/c x b/c and eight heterozygous loci (four RAPDs, and four RFLPs segregating in the pattern a/b x a/b (HZ loci)) were common to both maps. These 14 loci were used as bridges to align homologous groups between the two maps. In this case, RFLPs were more frequent and informative than RAPDs. Nine linkage groups in the MW25 map were homologous to six groups in the A19 map. In two cases, two or more bridge loci were common to a group; thus, the orientation of homologous linkage groups was also determined. In four other cases, only one locus was common to the two homologous groups and the orientation was unknown. Mdh, four RFLPs, and 14 RAPDs were assigned to chromosome L5, which also has the sex locus M.     

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.     

A cherry map from the inter-specific cross Prunus avium ‘Napoleon’ × P. nipponica based on microsatellite, gene-specific and isoenzyme markers

One hundred and sixty microsatellite (simple sequence repeat (SSR)) and six gene-specific markers revealing 174 loci were scored in 94 seedlings from the inter-specific cross of Prunus avium ‘Napoleon’ × Prunus nipponica accession F1292. The co-segregation data from these markers were used to construct a linkage map for cherry which spanned 680 cM over eight linkage groups with an average marker spacing of 3.9 cM per marker and just six gaps longer than 15 cM. Markers previously mapped in Prunus dulcis ‘Texas’ × Prunus persica ‘Earlygold’ allowed the cherry map to be anchored to the peach × almond map and showed the high level of synteny between the species. Eighty-four loci segregated in P. avium ‘Napoleon’ versus 159 in P. nipponica. The segregations of 32 isoenzyme loci in a subset of 47 seedlings from the progeny were scored, using polyacrylamide gel electrophoresis and/or isoelectric focusing separation followed by activity staining, and the co-segregation data were analysed along with those for 39 isoenzymes reported previously and for the 174 sequence-tagged site loci plus an additional two SSR loci. The second map incorporates 233 loci and spans 736 cM over eight linkage groups with an average marker spacing of 3.2 cM per marker and just two gaps greater than 15 cM. The microsatellite map will provide a useful tool for cherry breeding and marker-assisted selection and for synteny studies within Prunus; the gene-specific markers and isoenzymes will be useful for comparisons with maps of other rosaceous fruit crops. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular genetic linkage maps for allotetraploid Leymus wildryes (Gramineae: Triticeae).

Molecular genetic maps were constructed for two full-sib populations, TTC1 and TTC2, derived from two Leymus triticoides x Leymus cinereus hybrids and one common Leymus triticoides tester. Informative DNA markers were detected using 21 EcoRI-MseI and 17 PstI-MseI AFLP primer combinations, 36 anchored SSR or STS primer pairs, and 9 anchored RFLP probes. The 164-sib TTC1 map includes 1069 AFLP markers and 38 anchor loci in 14 linkage groups spanning 2001 cM. The 170-sib TTC2 map contains 1002 AFLP markers and 36 anchor loci in 14 linkage groups spanning 2066 cM. Some 488 homologous AFLP loci and 24 anchor markers detected in both populations showed similar map order. Thus, 1583 AFLP markers and 50 anchor loci were mapped into 14 linkage groups, which evidently correspond to the 14 chromosomes of allotetraploid Leymus (2n = 4x = 28). Synteny of two or more anchor markers from each of the seven homoeologous wheat and barley chromosomes was detected for 12 of the 14 Leymus linkage groups. Moreover, two distinct sets of genome-specific STS markers were identified in these allotetraploid Leymus species. These Leymus genetic maps and populations will provide a useful system to evaluate the inheritance of functionally important traits of two divergent perennial grass species.     

QTL analysis of flower and fruit traits in sour cherry

The map locations and effects of quantitative trait loci (QTLs) were estimated for eight flower and fruit traits in sour cherry (Prunus cerasus L.) using a restriction fragment length polymorphism (RFLP) genetic linkage map constructed from a double pseudo-testcross. The mapping population consisted of 86 progeny from the cross between two sour cherry cultivars, Rheinische Schattenmorelle (RS)×Erdi Botermo (EB). The genetic linkage maps for RS and EB were 398.2 cM and 222.2 cM, respectively, with an average interval length of 9.8 cM. The RS/EB linkage map that was generated with shared segregating markers consisted of 17 linkage groups covering 272.9 cM with an average interval length of 4.8 cM. Eleven putatively significant QTLs (LOD >2.4) were detected for six characters (bloom time, ripening time, % pistil death, % pollen germination, fruit weight, and soluble solids concentration). The percentage of phenotypic variation explained by a single QTL ranged from 12.9% to 25.9%. Of the QTLs identified for the traits in which the two parents differed significantly, 50% had allelic effects opposite to those predicted from the parental phenotype. Three QTLs affecting flower traits (bloom time, % pistil death, and % pollen germination) mapped to a single linkage group, EB 1. The RFLP closest to the bloom time QTL on EB 1 was detected by a sweet cherry cDNA clone pS141 whose partial amino acid sequence was 81% identical to that of a Japanese pear stylar RNase. Received: 4 March 1999 / Accepted: 27 August 1999     

The first genetic and comparative map of white lupin (Lupinus albus L.): identification of QTLs for anthracnose resistance and flowering time, and a locus for alkaloid content.

We report the first genetic linkage map of white lupin (Lupinus albus L.). An F8 recombinant inbred line population developed from Kiev mutant x P27174 was mapped with 220 amplified fragment length polymorphism and 105 gene-based markers. The genetic map consists of 28 main linkage groups (LGs) that varied in length from 22.7 cM to 246.5 cM and spanned a total length of 2951 cM. There were seven additional pairs and 15 unlinked markers, and 12.8% of markers showed segregation distortion at P < 0.05. Syntenic relationships between Medicago truncatula and L. albus were complex. Forty-five orthologous markers that mapped between M. truncatula and L. albus identified 17 small syntenic blocks, and each M. truncatula chromosome aligned to between one and six syntenic blocks in L. albus. Genetic mapping of three important traits: anthracnose resistance, flowering time, and alkaloid content allowed loci governing these traits to be defined. Two quantitative trait loci (QTLs) with significant effects were identified for anthracnose resistance on LG4 and LG17, and two QTLs were detected for flowering time on the top of LG1 and LG3. Alkaloid content was mapped as a Mendelian trait to LG11.     

Genetic linkage maps constructed by using an interspecific cross between Japanese and European pears

Genetic linkage maps of the European pear ( Pyrus communis L.) cultivar 'Bartlett' and the Japanese pear ( Pyrus pyrifolia Nakai) cultivar 'Housui' were constructed based on AFLPs, SSRs from pear, apple and Prunus, isozymes and phenotypic traits by using their F(1) progenies. The map of the female parent Bartlett consisted of 226 loci including 175 AFLPs, 49 SSRs, one isozyme and one S locus on 18 linkage groups over a total length of 949 cM, while that for 'Housui' contained 154 loci including 106 AFLPs, 42 SSRs, two phenotypic traits and the other four markers on 17 linkage groups encompassing a genetic distance of 926 cM. These maps were partially aligned using 20 codominant markers which showed segregating alleles in both parents. Compared with the reports of apple genetic maps, these pear maps were not saturated but were near saturation. Distorted segregation was observed in two and one regions of the genome of Bartlett and Housui, respectively. The position of 14 SSRs originating from apple could be successfully determined in pear maps, which enabled us to compare the two maps. Some SSRs developed from Prunus (peach, cherry) were also mapped. The relationships between pear and the other species belonging to the Rosaceae were discussed based on the position of SSRs.     

Microsatellite and AFLP markers in the Prunus persica [L. (Batsch)]×P. ferganensis BC1linkage map: saturation and coverage improvement

A set of 146 single sequence repeats (SSRs) and 14 amplified fragment length polymorphism (AFLP) primer combinations were used to enrich a previously developed linkage map obtained from a (Prunus persica×P. ferganensis)×P. persica BC₁ progeny. Forty-one SSR primer pairs gave polymorphic patterns detecting 42 loci. The restriction/selective primer AFLP combinations produced a total of 79 segregating fragments. The resulting map is composed of 216 loci covering 665 cM with an average distance of 3.1 cM. Novel regions were covered by the newly mapped loci for a total of 159 cM. Eight linkage groups were assembled instead of the earlier 10 as two small groups (G1a and G8b), previously independent, were joined to their respective major groups (G1b and G8a). Several gaps were also reduced resulting in an improved saturation of the map. Twelve gaps ≥10 cm are still present. A comparative analysis against the Prunus reference map (71 anchor loci) pointed out an almost complete synteny and colinearity. Six loci were not syntenic and only two were not colinear. Genetic distances were significantly longer in our map than in the reference one.     

A genetic linkage map for hexaploid,cultivated oat (Avena sativa L.) based on an intraspecific cross 'Ogle/MAM17-5'

Genetic research and breeding of oat ( Avena sativa L.) would be aided by development of a genetic linkage map for a breeding population. Such a map could be used for localization of qualitative and quantitative trait loci, marker-assisted selection and other genetic analysis in an adapted, agronomically useful background. The objectives of this research were to develop a genetic linkage map of hexaploid cultivated oat, to identify homoeologous relationships of linkage groups, and to compare homologous linkage groups between this map and the previously published hexaploid oat map from the cross 'Kanota/Ogle' (KO). A total of 510 markers, including 172 restriction fragment length polymorphisms (RFLP), 324 amplified fragment length polymorphisms (AFLP) and 14 simple sequence repeats (SSR), were assessed on a recombinant inbred population of 152 F(5:6) lines derived from the cross, 'Ogle/MAM17-5' (OM). Twenty eight linkage groups of 5 cM or longer were formed using 476 of the markers, while 34 markers remained either unlinked or in small fragments less than 5 cM. The 28 linkage groups contained from 3 to 33 markers, and varied in size from 5.2 to 123.0 cM, representing a total map length of 1,396.7 cM. Three putative homoeologous groups (OM7, OM8 and OM18; OM2 and OM23; OM13 and OM16) were identified. Comparison with the published KO map indicated that nine OM linkage groups could be determined to be homologous to linkage groups in the KO map. Further comparison of the homologous linkage groups revealed that residual differences in genomic rearrangements existed between the two hexaploid oat populations. Some linkage groups were significantly extended compared with the KO map. Since the OM mapping population is segregating for a number of agronomically important traits, this genetic map will provide a useful tool for identification of qualitative and quantitative loci for these traits.     

A genetic linkage map and comparative genome analysis of common carp (Cyprinus carpio L.) using microsatellites and SNPs

A genetic linkage map is a powerful research tool for mapping traits of interest and is essential to understanding genome evolution. The aim of this study is to provide an expanded genetic linkage map of common carp to effectively carry out quantitative trait loci analysis and conduct comparative mapping analysis between lineages. Here, we constructed a genetic linkage map of common carp (Cyprinus carpio L.) using microsatellite and single-nucleotide polymorphism (SNP) markers in a 159 sibling family. A total of 246 microsatellites and 306 SNP polymorphic markers were genotyped in this family. Linkage analysis using JoinMap 4.0 organized 427 markers (186 microsatellites and 241 SNPs) to 50 linkage groups, ranging in size from 1.4 to 130.1 cM. Each group contained 2-30 markers. The linkage map covered a genetic distance of 2,039.2 cM and the average interval for markers within the linkage groups was approximately 6.4 cM. In addition, comparative genome analysis within five model teleost fish revealed a high percentage (74.7%) of conserved loci corresponding to zebrafish chromosomes. In most cases, each zebrafish chromosome comprised two common carp linkage groups. The comparative analysis also revealed independent chromosome rearrangements in common carp and zebrafish. The linkage map will be of great assistance in mapping genes of interest and serve as a reference to approach comparative mapping and enable further insights into the comprehensive investigations of genome evolution of common carp.     

The potential of Prunus davidiana for introgression into peach [Prunus persica (L.) Batsch] assessed by comparative mapping

The potential for introgression of Prunus davidiana, a wild species related to peach, was evaluated with respect to problems of non-Mendelian segregation or suppressed recombination which often hamper breeding processes based on interspecific crosses. Three connected (F1, F2 and BC2) populations, derived from a cross between P. davidiana clone P1908 and the peach cultivar Summergrand were used. The intraspecific map of P. davidiana already established using the F1 progeny was complemented, and two interspecific maps, for the F2 and BC2 progenies, were built with a set of markers selected from the Prunus reference map. With the molecular data collected for the F2 map construction, regions with distorted marker segregation were detected on the genome; one third of all loci deviated significantly from the expected Mendelian ratios. However, some of these distorted segregations were probably not due to the interspecific cross. On linkage group 6, a skewed area under gametic selection was most likely influenced by the self-incompatibility gene of P. davidiana. Using anchor loci, a good colinearity between the three maps built and the Prunus reference map was demonstrated. Comparative mapping also revealed that homologous recombination occurred normally between P. davidiana and the Prunus persica genome. This confirmed the closeness of the two species. Higher recombination rates were generally observed between P. davidiana and P. persica than between Prunus amygdalus and P. persica. The consequences for plant breeding strategy are discussed. The three maps of the F1, F2 and BC2 progenies provide useful tools for QTL detection and marker-assisted selection, as well as for assessing the efficiency of the peach breeding scheme applied to introgress P. davidiana genes into peach cultivated varieties.     

花椰菜遗传图谱的构建及NBS-LRR类抗性同源基因在图谱中的定位

利用AFLP和NBS profiling技术, 以花椰菜自交系“AD白花”与高代自交不亲和系“C-8”杂交得到的F1代自交产生的F2代分离群体为材料, 构建了第一个花椰菜遗传连锁图谱。该图谱由234个AFLP标记和21个NBS标记构成了9个连锁群, 总图距为668.4 cM, 标记间平均距离为2.9 cM。每个连锁群包含的位点数从12到47个, 相邻两标记之间的距离范围是0~14.9 cM。NBS标记分布在8个连锁群中, 这些标记大部分聚在一起。本研究为今后的基因定位及重要农艺性状的分析提供框架图。此外, 研究NBS profiling 方法在花椰菜中的稳定性和有效性以及NBS-LRR类RGA在花椰菜基因组中的分布和特点。     

Genetic analysis of floral anthocyanin pigmentation traits in Asiatic hybrid lily using molecular linkage maps

To understand the genetic background of two floral anthocyanin pigmentation traits, anthocyanin pigmentation in the flower tepals and spot formation, in the Asiatic hybrid lily (2n = 24), segregation of the two traits among 96 F₁ plants derived from a cross between commercial cultivars 'Montreux' and 'Connecticut King' were investigated. 'Montreux' has anthocyanin pigmentation in the tepals with many spots, and 'Connecticut King' has flowers with carotenoid pigmentation without spots. The F₁ plants with or without anthocyanin pigment in the tepals segregated with a 1:1 segregation ratio, indicating that a single gene controls anthocyanin pigmentation in the tepals. The number of spots per square centimeter of all tepals showed continuous distribution in the F₁ plants. To map the loci for the two anthocyanin pigmentation traits, molecular linkage maps in the Asiatic hybrid lily were constructed using a double pseudo-testcross strategy, with the same F₁ plants used for phenotypic evaluation, and 212 PCR-based DNA markers. The trait for anthocyanin pigmentation in tepals was used as a trait marker. The map of 'Montreux' comprised 95 markers in 26 linkage groups, and the map of 'Connecticut King' used 119 markers in 24 linkage groups. The total map lengths were 867.5 and 1,114.8 cM, respectively. The trait locus for anthocyanin pigmentation in the tepals was between markers ASR35-180 and P506-40 in linkage group 1 of the 'Montreux' map with a map distance of 1.2 cM and 2.6 cM, respectively. A single-point analysis of quantitative trait loci (QTLs) for tepal spot number identified two putative QTLs in linkage groups 1 and 19 of the 'Connecticut King' map. One putative QTL in linkage group 19 explained 64% of the total phenotypic variation. Because both putative QTLs were mapped on the linkage map of 'Connecticut King' that has no spots, dominant alleles of them might suppress spot formation.     

Integration of sequence tagged microsatellite sites to the chickpea genetic map

Fifty sequence-tagged microsatellite site (STMS) markers and a resistant gene-analog (RGA) locus were integrated into a chickpea ( Cicer arietinum L., 2n = 2 x = 16 chromosomes) genetic map that was previously constructed using 142 F(6)-derived recombinant inbred lines (RILs) from a cross of C. arietinum x Cicer reticulatum Lad. The map covers 1,174.5 cM with an average distance of 7.0 cM between markers in nine linkage groups (LGs). Nine markers including the RGA showed distorted segregation ( P < 0.05). The majority of the newly integrated markers were mapped to marker-dense regions of the LGs. Six co-dominant STMS markers were integrated into two previously reported major quantitative trait loci (QTLs) conferring resistance to Ascochyta blight caused by Ascochyta rabiei (Pass.) Labr. Using common STMS markers as anchors, three maps developed from different mapping populations were joined, and genes for resistance to Ascochyta blight, Fusarium wilt (caused by Fusarium oxysporum Schlechtend.: Fr. f. sp. ciceris), and for agronomically important traits were located on the combined linkage map. The integration of co-dominant STMS markers improves the map of chickpea and makes it possible to consider additional fine mapping of the genome and also map-based cloning of important disease resistance genes.     

A preliminary microsatellite genetic map of the ostrich (Struthio camelus)

Molecular genetic maps can provide information for the identification and localization of major genes associated with quantitative traits. However, there are currently no published genetic linkage maps for any ratites. Herein, a preliminary genetic map of ostrich was developed using a two-generation ostrich reference family by linkage analysis of 104 polymorphic microsatellite markers, including 40 novel markers reported in this study. A total of 35 microsatellite markers were placed into 13 linkage groups. Five linkage groups are composed of three or more loci, whereas the remaining eight groups each contained two markers. The sex-averaged map spans 365.4 cM. The marker interval of each linkage group ranges from 5.3 to 25.4 cM, and the average interval distance is 16.61 cM. The male map covers 342.7 cM, with an average intermarker distance of 15.58 cM, whereas the female map is 456.7 cM, with the average intermarker spacing of 20.76 cM. In order to screen the orthologous loci between ostrich and chicken, all of the flanking sequences of the 104 polymorphic loci, nine monomorphic loci and a further 12 reported microsatellite loci for ostrich were screened against the chicken genomic sequence using the BLAST algorithm (Altschul et al., 1990), and corresponding orthologs were found for 13 sequences. The microsatellite loci and genetic map developed in this study will be useful for QTL mapping, population genetics and phylogenetic studies in the ratite. In addition, the 13 orthologous loci identified in this study will be advantageous to the construction of a comparative genetic map between chicken and ostrich.     

An amplified fragment length polymorphism map of the silkworm

The silkworm (Bombyx mori L.) is a lepidopteran insect with a long history of significant agricultural value. We have constructed the first amplified fragment length polymorphism (AFLP) genetic linkage map of the silkworm B. mori at a LOD score of 2.5. The mapping AFLP markers were genotyped in 47 progeny from a backcross population of the cross no. 782 x od100. A total of 1248 (60.7%) polymorphic AFLP markers were detected with 35 PstI/TaqI primer combinations. Each of the primer combinations generated an average of 35.7 polymorphic AFLP markers. A total of 545 (44%) polymorphic markers are consistent with the expected segregation ratio of 1:1 at the significance level of P = 0.05. Of the 545 polymorphic markers, 356 were assigned to 30 linkage groups. The number of markers on linkage groups ranged from 4 to 36. There were 21 major linkage groups with 7-36 markers and 9 relatively small linkage groups with 4-6 markers. The 30 linkage groups varied in length from 37.4 to 691.0 cM. The total length of this AFLP linkage map was 6512 cM. Genetic distances between two neighboring markers on the same linkage group ranged from 0.2 to 47 cM with an average of 18.2 cM. The sex-linked gene od was located between the markers P1T3B40 and P3T3B27 at the end of group 3, indicating that AFLP linkage group 3 was the Z (sex) chromosome. This work provides an essential basic map for constructing a denser linkage map and for mapping genes underlying agronomically important traits in the silkworm B. mori L.     

A first-generation microsatellite linkage map of the Japanese quail

A linkage map of the Japanese quail (Coturnix japonica) genome was constructed based upon segregation analysis of 72 microsatellite loci in 433 F(2) progeny of 10 half-sib families obtained from a cross between two quail lines of different genetic origins. One line was selected for long duration of tonic immobility, a behavioural trait related to fearfulness, while the other was selected based on early egg production. Fifty-eight of the markers were resolved into 12 autosomal linkage groups and a Z chromosome-specific linkage group, while the remaining 14 markers were unlinked. The linkage groups range from 8 cM (two markers) to 206 cM (16 markers) and cover a total map distance of 576 cM with an average spacing of 10 cM between loci. Through comparative mapping with chicken (Gallus gallus) using orthologous markers, we were able to assign linkage groups CJA01, CJA02, CJA05, CJA06, CJA14 and CJA27 to chromosomes. This map, which is the first in quail based solely on microsatellites, is a major step towards the development of a quality molecular genetic map for this valuable species. It will provide an important framework for further genetic mapping and the identification of quantitative trait loci controlling egg production and fear-related behavioural traits in quail.     

A genetic map constructed using a doubled haploid population derived from two elite Chinese common wheat varieties

Genetic mapping provides a powerful tool for the analysis of quantitative trait loci (QTLs) at the genomic level.Herein,we report a new genetic linkage map developed from an F1-derived doubled haploid (DH) population of 168 lines,which was generated from the cross between two elite Chinese common wheat (Triticum aestivum L.) varieties,Huapei 3 and Yumai 57.The map contained 305 loci,represented by 283 simple sequence repeat (SSR) and 22 expressed sequence tag (EST)-SSR markers,which covered a total length of 2141.7 cM with an average distance of 7.02 cM between adjacent markers on the map.The chromosomal locations and map positions of 22 new SSR markers were determined,and were found to distribute on 14 linkage groups.Twenty SSR loci showed different chromosomal locations from those reported in other maps.Therefore,this map offers new information on the SSR markers of wheat.This genetic map provides new opportunities to detect and map QTLs controlling agronomically important traits.The unique features of this map are discussed.