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Variation between species

All living things in the world are different; they show variation. The differences between species, e.g. cats, dogs, humans, polar bears occur because they have different genes. We list these characteristics and use them to define or classify each species.

Human Genes

A complicated set of chemical instructions is needed to build and control a human body. Nearly every cell in your body has these instructions in its nucleus, in 23 pairs of thread-like chromosomes. Small sections of these chromosomes are called genes. Each gene carries the instructions for a different characteristic.

Variation within species

There is also variation within a species which have basically the same genes eg. types of dog.

• Great Dane: big, strong.
• Golden retrever: strong, sleek, fast, long tail.
• Dalmation: spotted-black and white, fast.
• Grey Hound: fast, strong, clever.

Human characteristics

As human beings, we all have different features called characteristics. Some like eye colour are easy to see, and others like blood group are not so obvious. Most characteristics are passed onto you by your parents; they are inherited. We inherit one set from our mother and one set from our father. However, only one gene can control the hair colour. A black gene is dominant over blonde so you end up with black hair. Each of your parents also inherited two genes so it is a matter of chance which one you inherit. This is why there can be so much variation even within a family.

However variation can also be effected by the environment eg. weight depends on how much you eat, skin colour can change depending on how long your in the sun. No two people are exactly alike: height, weight, eye and skin colour, all show variation.

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