ABSTRACT
The genomic DNA contained in the nucleus of the cell can be gathered together into 23 pairs of chromosomes, 22 pairs that do not determine sex and 1 pair that does (the sex chromosomes, two X chromosomes in females and one X and one Y chromosome in males). Numbering of the chromosomes in the human cell is based roughly on their relative size; chromosome 1 is the largest, and chromosome 22 the smallest. However, this is unrelated to the number of genes on each chromosome. A current estimate of the number of genes in the human genome runs to between 30 000 and 40 000, but simply because a chromosome is larger doesn't mean it will definitely have more genes than its neighbor. Also, only around 2% of the human genome has protein-coding function, and so much of the genome is composed of stretches of DNA with, as yet, cryptic function.
