Conservation genetics – molecular detectives at work
Box 1 | What is genetics?
For all living things, there is a plan, or template, that dictates the form an organism will take. In almost every organism this template is deoxyribonucleic acid – DNA – and it is found in every cell of our bodies.
A molecule of DNA is a bit like a spiral staircase, consisting of two molecular ‘strands’ twisted into a double helix. Projecting from the strands are four different kinds of bases, or molecular sub-units – adenine (A), thymine (T), cytosine (C) and guanine (G). These come together to form base ‘pairs’, C bonding with G and T bonding with A, thereby joining the two strands together. In this way, the base pairs form the steps of the ‘staircase’.
What do these base pairs do? For many of the pairs in a DNA strand, the answer to this question is unknown. But for others, a sequence of three base pairs, or ‘steps’, forms a ‘codon’, which codes for one of 20 amino acids. These are the building blocks of proteins, which to a large extent determine the appearance of an organism and the way it works. A set of codons that codes for a given protein is called a gene – and gives its name to the science of genetics.
Different forms, or alleles, of the same gene result in the expression of different characteristics. For example, some people have blue eyes and others have green or brown because of slight differences in the sequence of codons that code for the genes that determine eye-colour.
Mutations
Over generations, the DNA changes, or mutates, as a result of chemical accidents during replication. The process of mutation is an essential force in nature. Charles Darwin hypothesised in the 1800s that sometimes a mutation would improve an organism’s chance of survival – a gene that gave better night-vision to a cat, for example, may increase the cat’s hunting prowess and therefore its ability to catch the food it needed to survive.
If a mutation proved beneficial, it would become more common because individuals that inherited it would be more likely to survive and to pass the mutation on to the next generation. This process of change is called ‘natural selection’ and is thought to be a major force in evolution.
The importance of variation
Difference between individuals – genetic variation – is thought by many conservation geneticists to hold the key to the long-term survival of species. Those species with a high degree of genetic diversity may prove more adaptable in the face of environmental change – such as exposure to a new disease or a change in climate. Some individuals will be unable to cope, but others may carry the genetic equipment they need to survive and thrive. Darwin called it ‘survival of the fittest’.
Boxes
Box 2. The problem of small populations
Box 3. Molecular detectives at work
Related sites
The search for DNA – the birth of molecular biology (Access Excellence, USA)
Reading the messages in genes (Access Excellence, USA)
Posted August 1999.