Brief introduction of genes and their mutations
Genes determine the characteristics of the human body
Genes determine many features of our bodies - growth, functioning, healing, appearance, diseases, immunity, and so on. Some aspects of our bodies are completely affected by our genes (eg eye colour) and some by the interaction between genes and the environment (eg weight).
Genes consist of a genetic code called DNA
In order to understand how genes work, we may imagine our bodies as a chain. All human organs and tissues are made up of cells which develop from one cell (formed by the sperm fertilizing the egg). Each cell has 46 chromosomes with 23 inherited by each parent. These chromosomes make up an individual’s genes. Genes consist of DNA which is a ‘code of information’ or a ‘genetic code’, made up of four chemicals (A - adenine, T - thymine, C - cytosine, and G - guanine) repeated in different combinations. Therefore, a gene is like a storage device containing all the information which predetermines every single characteristic of our body. In fact, the way in which the four chemicals are structured is the basis of every single human organ and tissue.
A genetic mutation is a fault in the genetic code
Sometimes, an error in the repetition of the four chemicals occurs, this creates faults in the genetic code of information leading to mutations in genes. Mutations in genes that control the cell cycle (oncogenes) may cause cells to start growing, multiplying and forming tumors. In other words, mutated genes send incorrect information to normal working cells which often results in tumors. Therefore, cancer in its simplest term is the name given to the disease of the cells. There are many different types of cancers, each with their own features and treatments. Though different, all cancers have one thing in common, each can be attributed to a mutation within one or more of the body’s cells.
Some tumors may be benign (not cancerous), some malignant (cancerous). Malignant cells can travel through the blood or lymphatic system and form tumors in different parts of the body. Mutations in genes that repair damaged DNA (tumor suppressor genes) cause mutations in cells not to be repaired and so the chances of forming tumors are much higher.
Cancer results from a mutation in genes
A mutation in an individual’s genes means that the growth, repair and death of the cells is no longer normal and often results in cells reproducing at an uncontrolled rate. There are two types of gene mutations. The first type, the acquired mutation, happens during a person’s lifetime by chance either due to the multiplication of cells or damaged genes. It is usually the result of genes interacting with the environment and or external factors called carcinogens, such as chemicals in cigarette smoke or radiation. The majority of cancers fall within this category.
While the acquired mutations cannot be passed on to other descendants, the second type, the inherited mutation, is the result of inheriting faulty genetic information from parents as half of one’s genes come from a father and the other half from a mother. If a mutated gene is passed on from one parent, it is called heterozygous, if from both parents, it is called homozygous. Therefore, if a person inherits a mutation from the parents, the mutation will be in the original cell and eventually in all of his or her subsequently formed cells. An inherited mutation does not mean that an individual has or will definitely develop cancer but inheriting a mutated gene significantly increases the chances of developing certain types of cancers, such as breast and ovarian cancer, particularly in combination with certain risk factors (age, lifestyle, the environment). Only 5-10% of cancers are inherited