Biology · Inheritance. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Variation means the differences between individuals of the same species. There are two types and you must be able to tell them apart.
Continuous variation gives a range of phenotypes between two extremes, with every value in between possible. Body length and body mass are examples. It is caused by genes and the environment together, for example diet affects mass.
Discontinuous variation gives a small number of separate phenotypes with no intermediates. A person is blood group A, B, AB or O and nothing in between. It is usually caused by genes only, so the environment does not change it.
Students call any feature with numbers "continuous". Ask instead: can an individual have any value in between? If the feature falls into fixed groups, it is discontinuous.
Answer: Discontinuous variation, caused by genes only.
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