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Home >>Molecular Maps of Plant Genome >>Cytogenic Maps Using Aneuploids
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Cytogenic Maps Using Aneuploids - Through a study of linkage of RFLP loci with morphological or biochemical (isozymes) markers having known chromosome location, it was possible to locate RFLP loci not only on specific chromosomes, but also on specific regions of these chromosomes.

For this purpose, monosomics (particularly in maize), trisomics and various available translocation or deletion stocks were also utilized. This resulted in the preparation of R'FLP chromosome maps for maize with more than 400 RFLP loci and those for tomato with more than 1000 loci.

The above technique also allowed mapping of duplicate loci, when more than one fragments homologous to a probe were detected on Southern blots. While in maize, 28.6% sequences detected duplicate loci, in tomato these duplicate loci were less that 2% of the loci tested. This gave new evidence about the, presence of frequent duplicate chromosome segments in maize rather than in tomato.

Molecular chromosome maps, are also being prepared for wheat, rye, barley, rice, etc. and the availability of aneuploids has greatly facilitated this work. For instance in wheat the use of nullisomic-tetrasomic lines facilitated the location of RFLP loci of specific chromosomes and the use of telocentrics allowed their location on specific arms.

This has thus allowed in wheat the identification of molecular markers for each of the 14 arms belonging to seven different homoeologous groups. In this connection, under the name 'International Triticeae Mapping Initiative (ITMI), international collaboration has been initiated to prepare maps for the tribe Triticeae and each homoeologous group has been assigned to one research group.

Three workshops to assess the progress made and to plan future work were organised in 1990, 1991 and 1992. Rapid progress in preparation of molecular maps of different species of the Triticeae are expected through these efforts.

Alien addition lines in wheat have also been utilized for assigning genes to specific chromosomes of the alien species involved. For instance wheat barley addition lines have been successfully utilized for assigning genes on specific barley chromosomes and wheat-rye addition lines are being used for a similar purpose for assining genes on specific rye chromosomes.

Genome specific probes (isolated from DNA of Aegilops squarrosa) have also been isolated to identify the D genome chromosomes in wheat and several other polyploid species carrying the D genome e.g. Ae. cylindrrica, CCDD; Ae. crassa, DDMM; Ae. ventricosa, DDUU. Recently, RFLP maps, of the seven chromosomes of the D genome chromosomes in heat have also been prepared through the use of genetic variability available in Aegilops squarrosa.

 
 

 

 
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