The Internet is mostly kittens but I think that this is my first picture of any. If you just want cute there is always the numbat. I chose this picture because these kittens all share the same parents, and although very similar in many ways, they also show variation. The variation you see between different individuals can either be genetically caused or environmentally caused. Some genes, like the genes for eye colour, can exist in different forms and these are known as alleles.
Genetic variation is the result of the characteristics inherited during fertilisation; the particular combination of genes that paired up when the zygote formed and any tiny copying errors that occurred during development (mutations). The most obvious characteristics that are controlled by genes are things like whether you can roll your tongue, eye colour, blood group or whether you are male or female. These characteristics are examples of discontinuous variation because there are only a certain number of blood groups or sexes that a person (or kitten) can be. They tend to be the result of only one or two alleles and they are not affected by environmental conditions.
Some characteristics can be influenced by the environment. For example, if you have the genes for being tall, they will only be fully expressed if you are well fed and healthy. Milk yield in dairy cows is affected by the animal’s genes but if it is not properly fed and watered its yield will be low. Characteristics like height, weight or hand-span are examples of continuous variation because, although there is likely a minimum and a maximum value, there can be any number in between. These characteristics tend to be governed by several different alleles.
Twig Prep has a very nice video on this topic.
Further reading: do check the other posts in this series, and the BBC Bitesize has a good series of short articles.
Questions…
- What does fertilisation mean?
- Which dietary nutrient is most important for growth and repair?
- How many pairs of chromosomes does a human have?
- From what chemical are genes made?
- Genes govern your inherited characteristics, but what does a single gene actually code for?
ps – I have come across quite a bit of controversy over this topic. For example, the idea that tongue rolling is only governed by dominant and recessive alleles has been shown to be wrong. It is usually, but not always, controlled by your genes – some people can be taught to roll their tongues. Likewise, eye colour is not as simple as brown, blue and green – there are variations in between. A small percentage of people have eye colour that is independent of the alleles possessed by their parents.
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