Chromosomes with structures that approximate each other will pair up together during cell division taking place in reproduction. The genes on the chromosomes that pair together will encode similar features such as hair or eye colour. The length of homologous chromosomes is also very similar; the only exception to this being sex cells where the X chromosome is considerably longer than the Y chromosome. Chromosomes occur in pairs and one member from each pair is inherited from one parent and the other member of the pair is inherited from the other parent.
Although we always learn that humans have 23 pairs of chromosomes, with a total of 46 chromosomes, there are actually many chromosomal abnormalities which mean either a malformation of a chromosome or having extra chromosomes and result in certain illnesses. For example, Down’s syndrome is due to the presence of one extra chromosome, which means having a total of 47 chromosomes. Another condition which affects only girls is the triple X syndrome in which females have an extra X chromosome (Polyploidy refers to the condition of having three homologous chromosomes rather then two).Click here to read more about our chromosomes.