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Variation just means differences between organismsAll living things in the world are different- we say that they show variation.Teeny-weeny bugs and huge donking elephants show obvious differences.But other variation is less obvious and hard to spot, e.g. a persons blood group

Different species have totally different genes1) A human, cow, a dandelion and a tree all look different because they are different species.2) But you also see variation within a species, i.e. plants or animals which have basically the same genes will also show differences between them, e.g. skin colour, height, flower size, etc.Any difference is known as a characteristic feature3) Characteristic features can be inherited ( come from your parents inherited via genes)  or they can be environmental (caused by your conditions and surroundings.

Continuous variation: the feature can only take certain values1) examples of this are things like height, weight, skin colour, intelligence  leaf area, etc. where the feature can have any value at all- within a certain range

 Discontinuous variation: the feature can only take certain values1) examples of things like this are eye colour or blood group, where there are just a few distinct options,  NOT a whole continuous range

Environmental and inherited variation in animals1) we inherited genes from our parents, and with them come and combination of both our parents' characteristics. this is inherited variation2) Environmental variation is all to do with the effect of "upbringing". People often say "we're all a product of our environment - which just means our abilities and the way we look and behave depend at least partly, on our upbringing3) Identical twins both inherit exactly the same genes, and obviously these control most of their characteristics.4) However one twin could, say, become much heavier if they ate a lot more. This would be a case of environmental variation 

Every other characteristic of animals (and humans) is affected by a MIXTURE of GENETIC and ENVIRONMENTAL factors. E.g. weight, skin colour, academic ability, athletic prowess etc.

Environmental and inherited variation in plants1) plants inherit characteristics through there genes just like animals do.2) But plants are affected much more by their environment than animals are.In particular, plants are affected big style by these four important factors1) Temperature      2) Sunlight3) Moisture           4) Soil conditionsJust a little more light and warmth or water may double the size of a plant- whereas any animal would be barley affected by the same changes in the environment.

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