The science of chromosomes: a very brief introduction
The human genome is best defined as the full possible range of genes in a typical human. These genes are divided among 24 different chromosomes: 22 autosomes, which are numbered, and two sex chromosomes, labelled as X and Y.
Males have both an X and a Y chromosome; females have two X chromosomes. We all have two copies of chromosomes 1 to 22, giving us a total of 46 chromosomes.
Each chromosome is made up of two identical ‘sister chromatids’, joined together at a point called the centromere. Each chromatid is essentially a very long, incredibly tightly coiled strand of DNA. It is in this DNA that our genes are located.
The name ‘chromosome’ derives from the Greek words chroma, colour, and soma, body. It refers to the fact that chromosomes are readily stained by certain dyes.
Recent imaging techniques (called SKY and FISH) allow each of the 24 types of chromosome in a cell to be picked out in a different colour. The chromosomes of the Human Genre Project are displayed in this fashion.
For more about genes, check out The Wellcome Trust’s chromosome browser.