What is a gene?

Imagine:

Your body is made of lego blocks.

You were put together according to a lego instruction book. The instruction book is very long and complicated. It has 46 chapters. Each chapter has many paragraphs.

You have a friend who is also made of lego blocks. He was put together according to an instruction book that is nearly the same as yours, but not quite. It has 46 chapters like yours, but a few of the paragraphs are different to yours. Most are the same but some are different. (For example, the 457th paragraph in chapter 25 of his instruction book is quite different to yours - it has instructions on how to make black hair, while yours has instructions on how to make red hair).

Now imagine there are 8 billion people made of lego blocks, and nearly all of them have the same instruction book, with slight variations.

A gene is simply a paragraph in this shared instruction book. Paragraph 457 in chapter 25 is a gene.

A related term is an "allele". Your paragraph 457 is different to your friend's - he has the "black hair" allele and you have the "red hair" allele. The gene is the same (it's paragraph 457, chapter 25 in everyone's instruction book) but the allele is different. People often confuse the terms (and in fact you will rarely hear the term "allele" in the general media).

So when you hear people talk about a gene for this or a gene for that, they mean a particular variation of a paragraph in the instruction book.

So now you know what a gene is, here are some pretty amazing facts:

The average person is made of approximately 10 trillion "lego blocks".

Each lego block contains a tiny copy of the instruction book. In fact, that's the only place you will actually find the instruction book.

Each lego block can read its own instruction book and use part of it to make more lego blocks!

Sound too far out to be true? Well, replace "lego block" with "cell", and I can assure you, this is how you and the rest of the animal and plant kingdom are made.

Truly astounding.