CHROMOSOMES ARE HIGHLY ELASTIC AND CAN BE STRETCHED

Direct manipulation of human chromosomes in metaphase spreads using gl ass needles revealed that the consistency of chromosomes varies depend ing on their moisture content. Chromosomes are soft and highly elastic under wet conditions and are hard when dry. The elasticity of chromos omes is comparable to rubber threads and can be used far stretching ex periments under phase contrast microscopy, after Giemsa staining, and after GTG-banding. The coiling structures of the chromosomes appear to be stretched evenly along the length of the chromosome. Chromosomes f ixed for only a short time have a tendency to tear when stretched more than 5 times their length. Under the experimental conditions used, ch romosomes were preferentially torn in the centromeric region. Chromoso me stretching on GTG-banded human chromosomes leads to a splitting of bands into their subbands. This may be useful for creating new high re solution ideograms possibly showing more than 1700 bands per haploid s et.