DNA determines a wide variety of proteins that makes up each organism. Similarities and differences between organisms may be defined in terms of variation of DNA.
A section of DNA that codes for one or more polypeptides is called a GENE. All members of the same species have the same genes. Different variations of genes are called ALLELES. It is the combination of alleles that an individual or species posses that makes them different from each other.
THE GREATER NUMBER OF ALLELES THAT ALL MEMBERS OF A SPECIES HAS, THE GREATER THE GENETIC DIVERSITY OF THAT SPECIES AND THE MORE LIKELY TO SURVIVE AND ADAPT TO ENVIRONMENTAL CHANGE
This is because they have a wider range of alleles, therefore a wider range of CHARACTERISTICS
Genetic diversity is reduced when a species has fewer different alleles so less likely to survive if the environment changes
Selective breeding is also known as ARTIFICIAL SELECTION where a breeder takes an individual in a species with desirable characteristics and uses them to breed from to produce offspring.
If these offspring do not have the desired characteristics they are killed or not used to breed from. This way, unwanted characteristics are bred out of the population.
BUT this makes the population deliberately have restricted alleles to only the desired alleles.
Over generations, this leads to the whole population having the same desired qualities (eg. Golden Retrievers - all white/gold) BUT with reduced genetic diversity
Selective breeding is commonly carried out to produce:
- High Yielding breeds of strains of plants
- Domestic animals
and to show desirable characteristics eg:
- Animals: Colour, height, fur
- Plants: Resisitance to disease, bigger grains, more sugar, bigger plants
The Founder Effect
Genetic Bottleneck Effect