Biology [[Classification, Selection and Evolution]] Variation

[[Variation]]

Genetic variation is caused in five ways
*Independant assortment of chromosomes
*crossig over between chromatids
*random mating within a species
*random fertilisation
*Mutation

Unlike the first four, mutation does more than reshuffle already present alleles. It can produce completely new alleles during gene mutation. This new allele is often recessive and does not show up in the population until generations after it occured.

Mutations in somatic (body) cells often hace no effect on the organism a malfunctioning cell in a tissue is one in thoudsands of cells and so it is unlikley that it would cause any issues.

Most mutated cells are recognised by the immune system and destroyed.

Occasionally, mutation can effect cell division. if such a cell escapes the immune system, it can produce a lump of cells called a tumor.

Tumors often cause little harm but can sometimes spread around the body and invade other tissues. theses are malignant. Diseases caused by theses types of tumers are known as cancers.

Somatic cell mutataions cannot be passed on to offspring, but mutation in cells of the ovaries or testes can be inherited. If a cell containing a mutation devides to form gametes then the gametes may also contain the mutated gene.

Genetic variation can be passed on by parents to thir offspring giving differences in phenotypes. Variation in phoenotypes caused by the environmnent are not passed on.