Chromosome

An entity which consists of a long DNA molecule which carries a large number of genes, as well as proteins and RNA associated with the expression of these genes. Human chromosomes have a size which varies between 1 and 10 thousandths of a millimetre whilst the DNA molecule they contain varies between 0.5 and 5 centimetres. The DNA molecule is in effect folded up on itself and wound onto the proteins.

A human being has 46 chromosomes, divided into 23 pairs, coming equally from the father and the mother. Other species have less (certain flies have 4), others many more (380 for some butterflies).