Mutations have worked hard over the last few millennia to turn us from bacteria into complex sentient life forms capable of writing on a world-wide electronic net.

The basics.

And for all that hard work they usually only get press only when we hear about cancers and genetic diseases, but they can not be all bad; lets not forget that we are who we are today because of them.

If a mutation was inherited from either you father's sperm or your mother egg it is a hereditary mutation.

A somatic mutation occurs in body cells and can not be inherited because the genes in the faulty cell have nothing to do with the sex cells.

With both types of mutations the chances of having a one increase with age because of the natural increase in errors that replicating DNA has. There is so much DNA to replicate that the few that do occur add up. The chances of giving birth the a child with Down's syndrome are

Hereditary mutations.

Hereditary mutations can sometimes be so severe that they cause the

Each cell needs instructions telling it how to act. Every cell in the body has the same genes, it is the active genes that keep the cell different (a brain cell a brain cell and not a blood cell). A woman has two X chromosomes, but one is turned off, is this a hereditary mutation? No, it is an example of the next type of mutation:

Somatic mutations.

Which X- chromosomes should be inactivate? Depends on the cells personal choice. X- inactivation occurs after the embryo has divided a few times; if the X-inactivation had occurred when there was only one cell then all the cells would be the same, but the delay means that all women are a mix of maternal and paternal X-chromosomes in their bodies. This can be seen graphically in red and black tortoise-shell coats of some cats.

A somatic mutation is something that has developed in your body and is not inheritable. An example of this is cancer (only a vulnerability to cancer can occur through genes). The cells of the human body are designed to work together co-operatively so they try to resist cancers themselves as well as being removed by the immune cells. How do cancers develop if the body fights them?

When DNA is replicated in cells during the natural process of repair and maintenance mistakes in the copying process occur; this is the basis of both types of mutations. Cells in the gut are removed (by apoptosis) and replaced every three days; this is a high division rate in cells and all that DNA copying needs to be done accurately.

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