Chromosomes are compact packages of DNA contained within single cells

Unraveled, the ultra-thin strands of DNA from a single human cell are about 3 meters long. The only way for the entire body to carry such vast amounts of DNA is by winding it into complex bundles, known as chromosomes, that take up less space inside the cell nuclei. We inherit 46 chromosomes from our parents, which are divided into 23 pairs. One chromosome from each pair comes from our father and the other from our mother. It is this mix of chromosomes from our parents that determine our characteristics, including our propensity to develop various diseases.

How genes are inherited, recombination & genetic reshuffling

The chromosomes you inherited from your parents were actually a mosaic of chromosomes they inherited from their parents, that is, your grandparents. This is due to a process called recombination. Recombination takes place when germ cells (egg or sperm) are produced, when large segments of DNA are exchanged between each pair of chromosomes. This kind of genetic shuffling means that any chromosome you inherited from your mother is in fact a mosaic of chromosomes she inherited from her parents, and so on. This reshuffling increases the possible number of combinations of genetic variants, which in turn ensures greater variability of characteristics among individuals.

How genes determine sex

Of the 23 chromosome pairs, 22 are known as autosomal, where the paired chromosomes are almost identical in size and content. The remaining pair consists of sex chromosomes, known as such because they carry the genes responsible for sex determination. For this pair, if you inherited an X chromosome from both mother and father, you are female. Alternatively, if you inherited an X chromosome from your mother and a Y chromosome from your father, then you are male. The X and Y chromosomes are very different in size and content.

This content was last reviewed on February 18, 2010.