Biology

Variation

Individuals in a population are usually similar to each other, but not identical. Some of this variation within a species is genetic, some is environmental, and some is a combination of both.

Genetic causes of variation

Each sperm cell and each egg cell contains half of the genetic information needed for an individual (each one is haploid - it has half the normal number of chromosomes). When these join at fertilisation, a new cell is formed. This zygote has all the genetic information needed for an individual (it is diploid - it has the normal number of chromosomes).

Examples of genetic variation in humans include blood group, skin colour and eye colour.

Environmental causes of variation

Characteristics of animal and plant species can be affected by factors such as climate, diet, accidents, culture and lifestyle. For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree…