written by: Rafael•edited by: Paul Arnold•updated: 6/15/2010
An essential guide to the structure and function of DNA, chromosomes and genes.
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The field of genetics has become big news. Hardly a day goes by without there being some mention in the newspapers of either a new gene discovery or a possible medical treatment based on an understanding of DNA and disease. The science has advanced rapidly in recent years; from the Human Genome Project to cloning animals and forensic technology. The developments are happening at a pace that many people find difficult to keep up with. If you're puzzled by genetics and want to know more, here's a good non-technical guide to the subject.
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What is DNA?
Inside the nucleus of every cell in your body (apart from red blood cells) are the instructions that tells the cell what job it has to do. These instructions are written in a very long molecule called DNA, which stands for deoxyribonucleic acid. The DNA molecule looks like a twisted ladder and is commonly referred to as a "double helix." The ladder is made up of 4 types of rungs known as bases. They are; A (adenine), C (cytosine), G (guanine), and T (thyamine).
There are millions of bases in each DNA molecule and they join together following a special set of rules. A will always pair with T, and C will always pair with G. Combinations of these letters, or bases will tell the cell to make proteins and it's these proteins that enable a cell to perform its specific function.
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DNA double helix
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What are chromosomes?
One of the main guiding principles of life is organization. Everything is organized within the body, within an organ, within the cell, and even within the nucleus of the cell. A long stretch of the DNA, millions of base pairs long,with some proteins attached to it, is organized in a rod-shaped superstructure called a chromosome.
Packed inside the nucleus are 46 chromosomes that are inherited from your parents. You get 23 from your father and 23 from your mother. The chromosomes contain all the information needed for a cell to live, grow, and succeed in life.
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What are genes?
Each chromosome within the nucleus of the cell contains thousands of genes. A gene is short region of DNA within a chromosome. It contains the specific instructions to make a protein.
There are billions genes inside the human body, but only about 30,000 different ones. That means in every nucleus in every cell there are 30,000 of them spread across the 46 chromosomes. But they don't all work at once in the same place. For example inside the nucleus of one of your heart cells will be the genes to make stomach acid or nose hair. But they are not turned on in the heart. They only function in the specific areas that they are needed. How the body carries out this neat trick is not fully understood.
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What is a mutation?
Occasionally there is a problem with the biological machinery. The DNA is built wrong, it's damaged in such a way that it cannot carry out its task. The change is permanent and if it happens in the sex cells, the eggs and sperm, it will be passed onto the next generation.
A mutation changes a gene's instructions for making a protein, causing the protein to malfunction or stop working. If this protein has a vital role to play in the body the consequences could be severe. Many genetic disorders and conditions are caused by mutations. It is important to remember that it's not a gene that causes a disease but a deleterious change to that gene. For example Cystic fibrosis is not caused by the CFTR gene, it is caused by mutations to that gene.
Mutations are not always dangerous, some will have no effect at all. They can happen at any time without you ever knowing about it. You can read more about the causes of mutations by clicking on this link
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The growth of genetics
The field of genetics is still in its infancy. The structure of DNA was only worked out in the 1950's. Since then there has been an exponential growth in many areas of research.
Knowing about these basic structures and processes will help us all to further understand the impact that genetics will have on our lives.