We have already seen that both sexual reproduction and mutations during asexual reproduction can lead to children that are different to their parents and different to each other. This is called Variation. Variation is important for a population for a number of reasons.
Variation enables a population to adapt to changing environmental conditions. For example, if the climate gets colder then members of the population who have more hair, or can cope with the low temperatures better, will survive. If there was no variation then all the members of the population would die out.
Variation also helps to keep genetic diseases to a minimum as the DNA with a mistake on it is mixed with other DNA that can mask out parts of the diseased DNA.
Types of Variation
The differences that arise from variation fall into two main types. There are the differences that form distinct groups, such as gender: you are either male or female. You cannot be both. This is discontinuous variation. On the other hand, the heights of people in a population can have a wide range of values. This is continuous variation.
There are four main blood types in humans (A, O, B, and AB). Every human has blood of one of those types and they cannot use blood (in a transfusion) from one of the others. This is an example of discontinuous variation. You can only have one of the four types - not any in-between types.
The blood group that you have is dependent upon your parents - the environment has no effect on which type you are.
Humans show a range of different heights even if they are all the same age. Males tend to be taller than females but even in a single sex there is a great deal of variation. Because people's heights don't group into a small number of set heights this sort of variation is called continuous variation.
Someone's height can also be affected by their environment: lack of healthy food, disease and access to warmth and shelter can all affect growth.
Measuring variations in hand span of people using this website.
Open your left hand and spread the fingers as wide as possible. Using a ruler measure the length between the tip of your thumb to the tip of your little finger in centimetres.
What does the graph tell us about the most common hand spans of people using the site?
Is there variation in hand spans?
The graph shows numbers of male and female subjects, is gender a factor?
Is the variation continuous or discontinuous?
Do you think that the people using this website were created sexually or asexually?