Genetics – Introduction

Introduction to genetics

Every part of our body is made up of millions of cells. We all began as a single cell, the fertilised egg that divided into two daughter cells which in turn divided to give four cells and so on. Through this amazing process of embryological development, supported by the nurturing environment of our mother’s womb, most of us ended up the right shape with all our organs in place and functioning as they should. The cells of the different tissues of the body have their own special job to do, their structure and behaviour being appropriate to that particular function. But what accounts for the different properties of specialised cells? Basically these differences stem from the varied combination of proteins which make up each cell and are needed to carry out the cell’s work. Cells are the basic building blocks of the body and proteins, the basic building blocks of the cell.

If you could look at your skin under a microscope you would see millions of tissue cells. In fact, every part of our body is made up of cells, rather like a house is made up of bricks. In the centre, or nucleus, of most cells in our body there are thread-like structures known as chromosomes. Chromosomes carry genes. We can think of genes as ‘strung’ along chromosomes, in much the same way as beads are strung along a necklace.

The action of the genes determines which proteins are produced in what cells. Genes provide the instructions about how to make a new baby from a sperm and an egg – not so much the blueprint as the instruction manual used to produce the body.

With very few exceptions, each cell has a full set of genes packaged into 46 tiny structures called chromosomes. Not all the genes are active in any one cell, just those appropriate to that cell type and the functions it must perform. Our genes not only guide our development from fertilised egg to fully grown adult, but go on providing the information that is needed for everyday maintenance and functioning of our bodies. Genes give us our physical characteristics including our eye colour, our ability to run fast as well as our susceptibility to disease.

For this reason an inherited genetic fault can cause errors of development that are manifest at birth or soon after, or cause a specific malfunction of the body.


Shown above: The relationship of DNA to chromosomes

Genes are made up of DNA (Deoxyribose Nucleic Acid). This is the material “stuff” in which the genetic instructions are written (the paper and ink). If there is a change or spelling mistake in the writing of the instruction manual, then the body is unable to function correctly because it has not received the correct instructions. The features of a genetic condition occur, or may occur, therefore, when there is a spelling mistake or change in the person’s genes.

The functioning of our bodies requires that many thousands of genes work together. Changes or spelling mistakes in different genes have resulted in many different genetic conditions, one of which is Ectodermal Dysplasia.

It is very important to remember that a person cannot choose or modify the genes that he or she has, and that the events of pregnancy do not change the genes. Thus, parents who have a child with ED should not think that they did anything to cause the defective gene and should not blame themselves in any way for having a child with a genetic disorder.

Looking Ahead
Advances in human genetics are expected to benefit us in many ways. Most direct is the help that can be offered to individuals and families threatened by serious inherited disease. Improved understanding of the molecular basis of such conditions will, in the long term, lead to better treatments including gene therapy. Even where that is not possible, many families find it helpful just to understand what has occurred, even if it cannot be changed.

More indirect, but of great potential benefit, is our ability to understand how genetic variation interacts with environmental factors to cause the common diseases, such as diabetes, heart disease and cancer. We hope that this work will lead to real improvements in the treatments and preventive approaches for many disorders.

The special nature of genetic information highlights certain ethical issues. This is an additional reason why scientists and clinicians should explain what they are doing and ensure they carry the public with them as they translate research findings into new diagnostic tests and treatments. Another reason for an educational drive to explain genetics is central to an understanding of biology, and given enough insight most people find genetics fascinating and it is a privilege to be living at such an exciting time in the development of human genetics.