VARIATIONThe difference between individuals of the same or different species

Objectives• Be able to• Define the term variation• Discuss the fact that variation occurs within as well as

between species• Describe the differences between continuous and

discontinuous variation using examples• Explain both genetic and environmental causes of

variation• Outline the behavioural, physiological and anatomical

adaptations of organisms to their environments.

Interspecific variation

• Differences between individuals of different species are used as criteria for classification

Intraspecific

• Within the same species there are differences

Causes of variation

• Genetic• The particular combination

of alleles passed on by two parents by sexual reproduction.

• Mutation during either sexual or asexual reproduction.

• Environmental• Plant features are easily

influenced by light, mineral nutrition, availability of water- especially the amount and direction of growth.

• Animal features may be influenced by diet, temperature, and developmental environment.

Example of environmental variation

Two types of variation

1 Discontinuous variation• A few discrete categories no intermediate forms

• Usually controlled by one gene

• Less likely to be influenced by environment

Two types of variation

2 Continuous• There is a range of many intermediates between two extremes

• Represented using a frequency histogram where the range has to be split up into classes

• Controlled by the influence of several genes ( polygenic)