Fragmentation of a Chromosome,DNA Segments,Diploid Yeast Cells,Chromosome Fragments

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	Fragmentation of a Chromosome - This involves breaking of a chromosome at the position of a cloned DNA segment. A technique for breaking the chromosome at the site of a cloned segment is available in yeast, where a diploid yeast cell is transformed twice. (i) First it is transformed with a small linear DNA molecule, one end of it having DNA segment to be mapped and the other end having the telomere. Due to recombination of this molecule with complete chromosome, a shortened stable DNA molecule is obtained.
(ii) The diploid yeast cells are again transformed with another linear DNA molecule, one end of which has DNA segment to be mapped and the other end has a telomere and a centromere on the opposite end (relative to linear molecule used in the first transformation). Recombination in this case will give another shortened chromosome with stable ends. The stable chromosome fragments (obtained from two separate transformations) and the cloned DNA segment can be positioned relative to the chromosome ends. Using the above technique three genes were mapped (MEL1, GAL1, LYS2). For this purpose, a number of different yeast chromosome fragmentation vectors (YCFI, YCF2, YCF3, YCF4) were utilized.