Modern ideas on chromosome structure.

The structural element of an eukaryotic chromosome is the so-called chromatin fibre. It is a DNA-protein complex of about 100-200 A thickness and most probably running through from one end of a chromatid to the other. The fine structure of this DNA-protein fibre suggests a core of globular histone subunits around which the DNA-molecule is wound. The single strandedness of chromatids is suggested by the structure of premature condensed chromosomes. The course G-banding seen in metaphase chromosomes is presumably caused by groups of much finer bands seen in decondensed chromosomes. The number of such fine bands in the human genome is estimated to be 10 000-100 000, figures which are in the range of the number of genes in man.