A genetic linkage map of lentil (Lens sp.) based on RAPD and AFLP markers using recombinant inbred lines

 A genetic linkage map of Lens sp. was constructed with 177 markers (89 RAPD, 79 AFLP, six RFLP and three morphological markers) using 86 recombinant inbred lines (F_6:8) obtained from a partially interspecific cross. The map covered 1073 cM of the lentil genome with an average distance of 6.0 cM between adjacent markers. Previously mapped RFLP markers were used as anchor probes. The morphological markers, pod indehiscence, seed-coat pattern and flower-color loci were mapped. Out of the total linked loci, 8.4% showed segregation distortion. More than one-fourth of the distorted loci were clustered in one linkage group. AFLP markers showed more segregation distortion than the RAPD markers. The AFLP and RAPD markers were intermingled and clustering of AFLPs was seldom observed. This is the most extensive genetic linkage map of lentil to-date. The marker density of this map could be used for the identification of markers linked to quantitative trait loci in this population. Received: 6 November 1997 / Accepted: 10 February 1998     

Identification of quantitative trait loci contributing to Fusarium wilt resistance on an AFLP linkage map of flax (Linum usitatissimum)

 An AFLP genetic linkage map of flax (Linum usitatissimum) was used to identify two quantitative trait loci (QTLs) on independent linkage groups with a major effect on resistance to Fusarium wilt, a serious disease caused by the soil pathogen Fusarium oxysporum (lini). The linkage map was constructed using a mapping population from doubled-haploid (DH) lines. The DH lines were derived from the haploid component of F₂ haploid-diploid twin seed originating from a cross between a polyembryonic, low-linolenic-acid genotype (CRZY8/RA91) and the Australian cultivar ‘Glenelg’. The AFLP technique was employed to generate 213 marker loci covering approximately 1400 cM of the flax genome (n=15) with an average spacing of 10 cM and comprising 18 linkage groups. Sixty AFLP markers (28%) deviated significantly (P<0.05) from the expected segregation ratio. The map incorporated RFLP markers tightly linked to flax rust (Melamspora lini) resistance genes and markers detected by disease resistance gene-like sequences. The study illustrates the potential of the AFLP technique as a robust and rapid method to generate moderately saturated linkage maps, thereby allowing the molecular analysis of traits, such as resistance to Fusarium wilt, that show oligogenic patterns of inheritance. Received: 8 December 1997 / Accepted: 7 April 1998     

Towards a saturated sorghum map using RFLP and AFLP markers

 A near-saturated sorghum genetic linkage map was produced using RFLP, AFLP and morphological markers. First a composite, essentially RFLP-based genetic linkage map was obtained from analyses of two recombinant inbred populations. This map includes 343 loci for 11 linkage groups spanning 1352 cM. Since this map was constructed with many previously mapped heterologous probes, it offers a good basis for synteny studies. Separately, an AFLP map was obtained from the analysis of 168 bands revealed from 12 primer pair combinations. It includes 137 loci for 11 linkage groups spanning 849 cM. Taking into account the different data sets, we constructed a combined genetic linkage map including 443 loci spanning 1899 cM. Two main features are to be noted: (1) the distribution of AFLPs along the genome is not uniform; (2) an important stretching of the former core map is induced after adding the AFLPs. Received: 10 May 1998 / Accepted: 13 July 1998     

Genetic mapping in pea. 1. RAPD-based genetic linkage map of Pisum sativum

 A genetic linkage map of Pisum sativum L. was constructed based primarily on RAPD markers that were carefully selected for their reproducibility and scored in a population of 139 recombinant inbred lines (RILs). The mapping population was derived from a cross between a protein-rich dry-seed cultivar ‘Térèse’ and an increased branching mutant (K586) obtained from the pea cultivar ‘Torsdag’. The map currently comprises nine linkage groups with two groups comprising only 6 markers (n=7 in pea) and covers 1139 cM. This RAPD-based map has been aligned with the map based on the (JI281×JI399) RILs population that currently includes 355 markers in seven linkage groups covering 1881 cM. The difference in map lengths is discussed. For this alignment 7 RFLPs, 23 RAPD markers, the morphological marker le and the PCR marker corresponding to the gene Uni were used as common markers and scored in both populations. Received: 13 March 1998 / Accepted: 29 April 1998     

Allotetraploidy of Zoysia species with 2n=40 based on a RFLP genetic map

 A RFLP linkage map of Zoysia spp. (2n=40), a warm-season turfgrass, was constructed by using the self-pollinated progenies obtained from an interspecific hybrid. Out of 115 DNA clones tested, 100 (87.0%), including 55 genomic clones, 38 cDNA clones, and seven gene clones encoding photosynthetic enzymes showed allelic-RFLP banding patterns among the parental accessions. We found that 26 probes detected two or more loci segregating in the self-pollinated progenies independently. The RFLP linkage map of Zoysia spp. consists of 115 loci in 22 linkage groups ranging in size from 12.5 cM to 141.3 cM with a total map distance of 1506 cM. Six RFLP loci (5.4%) showed significant segregation distortion (P<0.01). Two loci out of six were mapped to linkage group II, and another two loci were mapped to group VII. In the RFLP linkage map of zoysiagrass, five pairs of linkage groups sharing a series of duplicated loci with approximately the same order were identified. Therefore, we conclude that Zoysia spp. with 2n=40 should be considered as allotetraploids, which might have evolved from progenitors with a basic chromosome number of ten (x=10). Received: 20 March 1998 / Accepted: 17 September 1998     

Mapping of quantitative trait loci affecting Drechslera teres resistance in barley with molecular markers

 Resistance loci for seedling-stage resistance to net blotch disease (Drechslera teres) in barley were mapped with molecular markers in an F₂ population derived from a cross between the susceptible barley cultivar ‘Arena’ and the resistant Ethiopian landrace ‘Hor 9088’. Disease reactions were scored with first and second leaves of 2-week-old plants 7 and 9 days after inoculation with a single spore-derived isolate. For linkage analysis, 22 RFLP markers and 284 AFLP markers were used. The seven linkage groups covered 1153.3 cM with an average marker interval of 3.76 cM. The resistance was determined to be inherited in a quantitative manner. Altogether, 12 QTLs were mapped with positions depending on the leaf used for testing and the time period after infection. Heritability in the broad sense ranged between 0.21 and 0.37. Received: 26 May 1998 / Accepted: 9 June 1998     

Genetic linkage map in sour cherry using RFLP markers

 Restriction fragment length polymorphism (RFLP) linkage maps of two tetraploid sour cherry (Prunus cerasus L., 2n=4x=32) cultivars, Rheinische Schattenmorelle (RS) and Erdi Botermo (EB), were constructed from 86 progeny from the cross RS×EB. The RS linkage map consists of 126 single-dose restriction fragment (SDRF, Wu et al. 1992) markers assigned to 19 linkage groups covering 461.6 cM. The EB linkage map has 95 SDRF markers assigned to 16 linkage groups covering 279.2 cM. Fifty three markers mapped in both parents were used as bridges between both maps and 13 sets of homologous linkage groups were identified. Homoeologous relationships among the sour cherry linkage groups could not be determined because only 15 probes identified duplicate loci. Fifty nine of the markers on the linkage maps were detected with probes used in other Prunus genetic linkage maps. Four of the sour cherry linkage groups may be homologous with four of the eight genetic linkage groups identified in peach and almond. Twenty one fragments expected to segregate in a 1 : 1 ratio segregated in a 2 : 1 ratio. Three of these fragments were used in the final map construction because they all mapped to the same linkage group. Six fragments exhibited segregation consistent with the expectations of intergenomic pairing and/or recombination. Received: 1 April 1998 / Accepted: 9 June 1998     

A genetic map of Asparagus officinalis based on integrated RFLP, RAPD and AFLP molecular markers

 An integrated genetic map of the dioecious species Asparagus officinalis L. has been constructed on the basis of RFLP, RAPD, AFLP and isoenzyme markers. The segregation analysis of the polymorphic markers was carried out on the progeny of five different crosses between male and female doubled-haploid clones generated by anther culture. A total of 274 markers have been organized to ten linkage groups spanning 721.4 cM. Since the haploid chromosome number of asparagus is ten, the established linkage groups probably represent the different chromosomes; however, the only group associated with a specific chromosome is the one which includes sex, whose determinant genes have been located on chromosome 5. A total of 33 molecular markers (13 RFLPs, 18 AFLPs, 2 RAPDs and 1 isoenzyme) have been located on this chromosome. The closest marker to the sex determinant is the AFLP SV marker at 3.2 cM. Received: 26 March 1998 / Accepted: 30 April 1998     

A genetic linkage map of durum wheat

 A genetic linkage map of tetraploid wheat [Triticum turgidum (L.) Thell.] was constructed using segregation data from a population of 65 recombinant inbred lines (RILs) derived from a cross between the durum wheat cultivar Messapia and accession MG4343 of T. turgidum (L.) Thell. ssp dicoccoides (Korn.) Thell. A total of 259 loci were analysed, including 244 restriction fragment length polymorphisms (RFLPs), one PCR (polymerase chain reaction) marker (a sequence coding for a LMW (low-molecular-weight) glutenin subunit gene located at the Glu-B3 locus), seven biochemical (six seed-storage protein loci and one isozyme locus) and seven morphological markers. A total of 213 loci were mapped at a LOD≥3 on all 14 chromosomes of the A and B genomes. The total length of the map is 1352 cM and the average distance between adjacent markers is 6.3 cM. Forty six loci could not be mapped at a LOD≥3. A fraction (18.6%) of the markers deviated significantly from the expected Mendelian ratios; clusters of loci showing distorted segregation were found on chromosomes 1B, 3AL, 4AL, 6AL and 7AL. The durum wheat map was compared with the published maps of bread wheat using several common RFLP markers and general features are discussed. The markers detected the known structural rearrangements involving chromosomes 4A, 5A and 7B as well as the translocation between 2B-6B, but not the deletion on 2BS. This map provides a useful tool for analysing and breeding economically important quantitative traits and for marker-assisted selection, as well as for studies of genome organisation in small grain cereal species. Received: 5 January 1998 / Accepted: 31 March 1998     

Combined mapping of AFLP and RFLP markers in barley

AFLP marker technology allows efficient DNA fingerprinting and the analysis of large numbers of polymorphic restriction fragments on polyacrylamide gels. Using the doubled haploids from the F₁ of the cross Proctor × Nudinka, 118 AFLP markers were mapped onto a barley (Hordeum vulgare L.) RFLP map, also including five microsatellite and four protein marker loci. The AFLP markers mapped to all parts of the barley chromosomes and filled in the gaps on barley chromosomes 2L, 4L and 6 in which no RFLP loci had been mapped. Interestingly, the AFLP markers seldom interrupted RFLP clusters, but grouped next to them. The combined map covers 1873 cM, with a total of 282 markers. The merging of AFLP and RFLP markers increased the total map length; 402 cM were added to the map at the tips of chromosomes or in regions corresponding to earlier gaps. Another 375 cM resulted from mapping AFLP markers near to RFLP clusters or in between non-clustered RFLP markers.     

A linkage map of an F2 hybrid population of Antirrhinum majus and A. molle

To increase the utility of Antirrhinum for genetic and evolutionary studies, we constructed a molecular linkage map for an interspecific hybrid A. majus x A. molle. An F(2) population (n = 92) was genotyped at a minimum of 243 individual loci. Although distorted transmission ratios were observed at marker loci throughout the genome, a mapping strategy based on a fixed framework of codominant markers allowed the loci to be placed into eight robust linkage groups consistent with the haploid chromosome number of Antirrhinum. The mapped loci included 164 protein-coding genes and a similar number of unknown sequences mapped as AFLP, RFLP, ISTR, and ISSR markers. Inclusion of sequences from mutant loci allowed provisional alignment of classical and molecular linkage groups. The total map length was 613 cM with an average interval of 2.5 cM, but most of the loci were aggregated into clusters reducing the effective distance between markers. Potential causes of transmission ratio distortion and its effects on map construction were investigated. This first molecular linkage map for Antirrhinum should facilitate further mapping of mutations, major QTL, and other coding sequences in this model genus.     

Genomic structural differentiation in Solanum: comparative mapping of the A- and E-genomes

 A genetic map was constructed from an F₂ population of 76 individuals for the purpose of comparing the arrangement of loci in the A and E Solanum genomes. This progeny was derived from an interspecific cross between the species Solanum palustre×Solanum etuberosum, both of which are E-genome species. Two hundred and eighty one probes previously mapped in tomato and potato (A-genome, as postulated for diploid cultivated potato species by Matsubayashi 1991) disclosed 109 segregating loci in this population. Of these, 80 loci were linked in 19 linkage groups covering a total of 720.4 cM, with an average of 9 cM between markers. Although the genetic map of the E-genome showed conservation for most linkage groups with those of tomato and the A-genome, various translocations and possible inversions and transpositions were detected. It is evident that the accumulation of these structural changes in the E-genome is sufficient to cause the observed hybrid sterility. The major rearrangements in the E-genome included multiple translocations involving mosly linkage groups 2 and 8. Also a transposition was detected on group 9, with the same group-10 inversion distinguishing potato from tomato. Definitively groups 2, 8, 9 and 10, and possibly groups 1, 4 and 12, in the E-genome are structurally different from their homologues in the A-genome. In general, recombination values were larger in the E- than in the A-genome. The extensive structural differentiation of the E-genome with respect to that of potato and tomato justifies its present designation as a different genome, which is supported by previous chromosome-pairing studies. The difficult introgression of desirable traits from the Etuberosum species into potato can be explained by these structural differences. Received: 1 February 1998 / Accepted: 8 October 1998     

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.     

RFLP genetic linkage maps from four F(2.3) populations and a joinmap of Gossypium hirsutum L

An RFLP genetic linkage joinmap was constructed from four different mapping populations of cotton (Gossypium hirsutum L.). Genetic maps from two of the four populations have been previously reported. The third genetic map was constructed from 199 bulk-sampled plots of an F_2.3 (HQ95–6×’MD51ne’) population. The map comprises 83 loci mapped to 24 linkage groups with an average distance between markers of 10.0 centiMorgan (cM), covering 830.1 cM or approximately 18% of the genome. The fourth genetic map was developed from 155 bulk-sampled plots of an F_2.3 (119– 5 sub-okra×’MD51ne’) population. This map comprises 56 loci mapped to 16 linkage groups with an average distance between markers of 9.3 cM, covering 520.4 cM or approximately 11% of the cotton genome. A core of 104 cDNA probes was shared between populations, yielding 111 RFLP loci. The constructed genetic linkage joinmap from the above four populations comprises 284 loci mapped to 47 linkage groups with the average distance between markers of 5.3 cM, covering 1,502.6 cM or approximately 31% of the total recombinational length of the cotton genome. The linkage groups contained from 2 to 54 loci each and ranged in distance from 1.0 to 142.6 cM. The joinmap provided further knowledge of competitive chromosome arrangement, parental relationships, gene order, and increased the potential to map genes for the improvement of the cotton crop. This is the first genetic linkage joinmap assembled in G. hirsutum with a core of RFLP markers assayed on different genetic backgrounds of cotton populations (Acala, Delta, and Texas plain). Research is ongoing for the identification of quantitative trait loci for agronomic, physiological and fiber quality traits on these maps, and the identification of RFLP loci lineage for G. hirsutum from its diploid progenitors (the A and D genomes). Received: 23 February 2001 / Accepted: 8 June 2001     

RFLP mapping of the genes controlling hybrid breakdown in rice (Oryza sativa L.)

 Complementary recessive genes hwd1 and hwd2 controlling hybrid breakdown (weakness of F₂ and later generations) were mapped in rice using RFLP markers. These genes produce a plant that is shorter and has fewer tillers than normal plants when the two loci have only one or no dominant allele at both loci. A cultivar with two dominant alleles at the hwd1 locus and a cultivar with two dominant alleles at the hwd2 locus were crossed with a double recessive tester line. Linkage analysis was carried out for each gene independently in two F₂ populations derived from these crosses. hwd1 was mapped on the distal region of rice genetic linkage map for chromosome 10, flanked by RFLP markers C701 and R2309 at a distance of 0.9 centiMorgans (cM) and 0.6 cM, respectively. hwd2 was mapped in the central region of rice genetic linkage map for chromosome 7, tightly linked with 4 RFLP markers without detectable recombination. The usefulness of RFLP mapping and map information for the genes controlling reproductive barriers are discussed in the context of breeding using diverse rice germplasm, especially gene introduction by marker-aided selection.     

Development of an STS map of an interspecific progeny of Malus

Simple sequence repeat (SSR) markers developed from Malus, as well as Prunus, Pyrus and Sorbus, and some other sequence-tagged site (STS) loci were analysed in an interspecific F₁ apple progeny from the cross ‘Fiesta’ × ‘Totem’ that segregated for several agronomic characters. A linkage map was constructed using 259 STS loci (247 SSRs, four SCARs and eight known-function genes) and five genes for agronomic traits—scab resistance (Vf), mildew resistance (Pl-2), columnar growth habit (Co), red tissues (Rt) and green flesh background colour (Gfc). Ninety SSR loci and three genes (ETR1, Rt and Gfc) were mapped for the first time in apple. The transferability of markers from other Maloideae to Malus was found to be around 44%. The loci are spread across 17 linkage groups, corresponding to the basic chromosome number of Malus and cover 1,208 cM, approximately 85% of the estimated length of the apple genome. Interestingly, we have extended the top of LG15 with eight markers covering 25 cM. The average map density is 4.7 cM per marker; however, marker density varies greatly between linkage groups, from 2.5 in LG14 to 8.9 in LG7, with some areas of the genome still in need of further STS markers for saturation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Towards second-generation STS (sequence-tagged sites) linkage maps in conifers: a genetic map of Norway spruce ( Picea abies K.)

Genetic linkage maps have been produced for a wide range of organisms during the last decade, thanks to the increasing availability of molecular markers. The use of microsatellites (or Simple Sequence Repeats, SSRs) as genetic markers has led to the construction of “second-generation” genetic maps for humans, mouse and other organisms of major importance. We constructed a second-generation single-tree genetic linkage map of Norway spruce (Picea abies K.) using a panel of 72 haploid megagametophytes with a total of 447 segregating bands [366 Amplified Fragment Length Polymorphisms (AFLPs), 20 Selective Amplification of Microsatellite Polymorphic Loci (SAMPLs) and 61 SSRs, each single band being treated initially as a dominant marker]. Four hundred and thirteen markers were mapped in 29 linkage groups (including triplets and doublets) covering a genetic length of 2198.3 cM, which represents 77.4% of the estimated genome length of Picea abies (approximately 2839 cM). The map is still far from coalescing into the expected 12 chromosomal linkage groups of Norway spruce (2n = 2x = 24). A possible explanation for this comes from the observed non-random distribution of markers in the framework map. Thirty-eight SSR marker loci could be mapped onto 19 linkage groups. This set of highly informative Sequence Tagged Sites (STSs) can be used in many aspects of genetic analysis of forest trees, such as marker-assisted selection, QTL mapping, positional cloning, gene flow analysis, mating system analysis and genetic diversity studies. Received: 5 November 1997 / Accepted: 16 March 1998     

A Genetic linkage map of Pinyon pine (Pinus edulis) based on amplified fragment length polymorphisms

 Amplified fragment length polymorphisms (AFLP) were used to rapidly generate a dense linkage map for pinyon pine (Pinus edulis). The map population consisted of 40 megagametophytes derived from one tree at Sunset Crater, Arizona. A total of 78 primer combinations, each with three to five selective nucleotides, amplified 542 polymorphic markers. Of these, 33 markers showed significant deviation from the expected Mendelian genotypic segregation ratio of 1 : 1, and 164 showed complete linkage with another marker. This resulted in 338 unique markers mapping to 25 linkage groups, each of which ranged from 2 to 22 markers, averaging 80 centiMorgans (cM) in size and covering 2,012 cM (2,200 cM with the inclusion of 25 cM for each of 7 unlinked markers). Pairwise linkage values gave a genome size estimate of 2,390 cM, suggesting comprehensive coverage of the genome. A search for subsets of primer combinations giving the best map coverage found 10 primer combinations which together marked 72% of the linkage map to within 10 cM; an additional 10 primer combinations increased this percentage to 85%. Our map represents an initial step towards the identification of quantitative trait loci associated with pest resistance and water stress in pinyons and will further allow us to examine introgression rates between P. edulis and P. californiarum. Received: 14 October 1997 / Accepted: 29 April 1998     

Isolation and mapping of resistance gene analogs from the Avena strigosa genome

Degenerate primers based on conserved regions of the nucleotide binding site (NBS) domain (encoded by the largest group of cloned plant disease resistance genes) were used to isolate a set of 15 resistance gene analogs (RGA) from the diploid species Avena strigosa Schreb. These were grouped into seven classes on the basis of 60% or greater nucleic acid sequence identity. Representative clones were used for genetic mapping in diploid and hexaploid oats. Two RGAs were mapped at two loci of the linkage group AswBF belonging to the A. strigosa × A. wiestii Steud map, and ten RGAs were mapped at 15 loci in eight linkage groups belonging to the A. byzantina C. Koch cv. Kanota × A. sativa L. cv. Ogle map. A similar approach was used for targeting genes encoding receptor-like kinases. Three different sequences were obtained and mapped to two linkage groups of the hexaploid oat map. Associations were explored between already known disease resistance loci mapped in different populations and the RGAs. Molecular markers previously linked to crown rust and barley yellow dwarf resistance genes or quantitative trait loci were found in the Kanota × Ogle map linked to RGAs at a distance ranging from 0 cM to 20 cM. Homoeologous RGAs were found to be linked to loci either conferring resistance to different isolates of the same pathogen or to different pathogens. This suggests that these RGAs identify genome regions containing resistance gene clusters.     

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.