Biology 1- Variation

Variation in humans can be genetic or environmental

Variation in animals is due to genes and environment. Almost every aspec of a human or animal is affected by our environment in some way, however small. The factors that AREN'T affected in any way by environment are:

• Eye colour
• hair colour
• inherited disorbers (e.g. haemophilia, cystic fibrosis etc.)
• blood group

Varitation can be continuous or discontinuous.

Continuous variation shows a wide range of values, with an individual being anywhere on that scale e.g. height, weight.  Continuous variation tends to be quantative (can be measured), significantly affected  by the environment

 Discontinuous variation involves discrete values; and individual can only have one feature or another, with no inbetween values e.g. blood group, type of ear lobe. Discontinuous  variation tends to be qualitative (cannot be measure), usually unaffected by the envrionment.

Variation in plants is much greater. 

Plants are strongly affected by:

• sunlight,
• moisture level, 
• temperature,
• the mineral content of the soil

Sexual Reproduction

• Sexual reproduction is the process in which genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different. 
• causes variation
• In sexual reproduction the mother and the father produce gametes e.g. egg and sperm cells.
• In humans, each gamete contains 23 chromosomes- half the number of chromosomes in a normal cell. 

Asexual Reproduction

• reproduction without sex (only needs one parent)
• creates a genetixally identical offspring
• produces clones
• organsims that reproduce this way include yeast, bacteria and strawberry plants.

A mutation is a change in the DNA or chromosomes of a living organism. This can lead to changes in the features of the organism. Mutations can happen naturally or be caused by UV light and certain chemicals called mutagens. Mutations can lead to new characteristics, increasing variation.

If a mutation occurs in a reproductive cells, the offspring might develop abnormally or die. If a mutation occurs in a body cells, the mutant cells may start to multiply in an uncontrolled way and invade other parts of the body (cancer).

Ocassionally mutations are beneficial, and give an organism a survival advantage, so it can live on in conditions where others die. This is natural selection at work.