‘Carcinogens’ are substances that cause cancerous cell growth which affect the DNA in cells, resulting in mutations. For example, an individual that spends prolonged periods of time under ‘ultra violet’ light may develop a mutation in a somatic skin cell, and thus develop melanoma. Melanoma develops from . In melanoma the melanocytes start to grow and divide more quickly than usual and start to spread into the surrounding surface layers of skin. When they grow out of control they usually look like a dark spot or mole on your skin. Melanoma is a cancer which usually starts in the skin, either in a mole or in normal-looking skin. As the mutation took place in a somatic cell the subsequent cancer will not be passed on genetically to the ensuing generation.
Most mutations are harmful to the organism concerned. However, beneficial mutations to occur; though they are very rare and they may give a selective advantage to an organism.
A mutation that occurs in a germinal cell affects the gametes produced by the organism. In most cases, such mutations wouldn't even be noticed by the individual. However, these mutations, in contrast to the somatic mutations, will be passed on to the next generation, because they occur in the cells that could potentially form a zygote with another gamete.
Mutations that occur in gametes can cause unexpected and distinct differences between individuals. This is therefore the basis for ‘discontinuous variation”.
Discontinuous variation is variation within a population of a characteristic that falls into two or more discrete classes. Classic examples include such things as eye colour in animals and the tall and short pea phenotypes used by Austrian botanist Gregor Johann Mendel. Characteristics that display discontinuous variation are present in one state or another; there is no blending or merging of the different forms possible. Unlike continuous variation, discontinuous variation is displayed by characteristics that are usually controlled by only one or two genes and that have little or no environmental component in their expression.
Mendel also studied flower colour in peas, of which there were two distinct , purple and white. These are caused by two different of a single for color: the purple stands for the ability to make purple pigment, and the white stands for a lack of ability to form purple pigment, resulting in whiteness. Indeed in general it is often found that contrasting are determined by different of a single , as Mendel found for petal color. The specific set of carried by an individual is called the , which is the hereditary underpinning of the .
Mendle’s research highlighted the colossal differnces a solitary allele can have on the phenotype of an organism; and how such a slight disparity can have extensive effects i.e. colour or height of the organism.
