About Genes

DNA (Deoxyribonucleic acid) is a molecule that is present in every cell of our bodies and carries all the genetic information needed to make our bodies function. DNA is contained within the core or nucleus of each cell in a tightly packed structure called a chromosome.

The structure of DNA was worked out by two scientists, Francis Crick and James Watson, in 1953. They concluded that DNA is made up of two long strands paired up in the famous double helix.

Each one of these strands is made up of four components called bases: adenine (A); guanine (G); thymine (T); and cytosine (C). Millions of these bases run along the strand and it is the specific arrangement of these bases that makes up the code from that all the components of a cell are made.

Genes are a subunit of DNA. There are 30,000 to 40,000 genes and each gene carries the instructions to a make a single protein - the basic building blocks of any organism.

Genes are read by a substance in the cell called mRNA, which acts as the messenger, carrying the instructions for making a protein from DNA to the protein-making factory of the cell.

Once at the factory, the code is translated and the protein it codes for is made. Depending on what the protein’s role is in the body, it will either remain within the cell, or be transported to where it can carry out its function. All the proteins made by our cells interact in complex ways to ensure that our bodies function.

In order for our cells to divide, DNA must be continuously replicated, but mistakes are sometimes made when DNA is copied and the wrong letter is added or a letter is omitted. Cells do have a mechanism in place to check and correct these mistakes, but occasionally the mistakes go uncorrected, resulting in a mutated gene. If the gene isn’t correct, then the protein the gene codes isn’t made properly and it can’t carry out its specific function within the body.

Did you know?

There are approximately 100 trillion (100,000,000,000,000) cells in our bodies

The human genome contains 3164.7 million chemical bases (A, C, T, and G).

If you unwound and tied together the strands of DNA in one cell, it would stretch almost 6 feet.

If the DNA in all the cells of our body were put end-to-end, it would reach to the sun and back over 600 times

It would take 50 years to type the code of the entire human genome, if a person typed for eight hours a day at a rate of 60 words per minute.

Pre-implantation genetic diagnosis (PGD)
Some gene mutations lead to genetic diseases that can be passed down from generation to generation. If you carry such a mutation, then having a child can be like rolling a dice as to whether you will have a healthy child or a child with a disease. In the past, the only options were to consider not having children or to wait for a pre-natal test during pregnancy. If this test came back showing the foetus carried the disease, the parents then had the option of terminating the pregnancy.

However, genetic developments are now offering another option - during IVF the embryo can be tested before it is re-implanted to ensure that only embryos free of the genetic disease are re-implanted. This process is known as Pre-Implantation Genetic Diagnosis. During IVF the eggs are 'harvested' and fertilised with the sperm outside the body. They are then allowed to grow for three days, until they reach the eight-cell stage, when a biopsy is done and one cell is removed, which is tested for the genetic disease.

The argument over when you think 'life' begins can dictate your opinion on PGD and whether parents should be allowed to screen embryos. PGD does enable families with a terrible hereditary genetic disease to ensure they have a healthy child, however it is not available in all countries. In the US, it is up to the individual physicians and IVF clinics to whether they offer PGD, while, in the UK, it is strictly regulated by the Human Fertilisation and Embryo Authority. In some countries like Germany, it is banned completely.

In 2000, the Nash family were the first family in the world to use the technology offered by PGD to ensure a child who was not only free of a hereditary genetic disease but also a perfect bone marrow match for their elder daughter who was dying of Fanconi Anaemia.

Did you know?
Each of us carries about six defective genes, but we don’t suffer the harmful effects of the mutation because we only have one copy of the defective gene.

One in 10 people will develop an inherited genetic disorder at some stage in their lives.

Not all gene defects are detrimental to our health. In sickle cell anaemia, one copy of the sickle cell gene gives resistance against malaria.