Genetic diversity exists within a species. The DNA within a species varies very little though.
All the members of the species will have the same genes but different alleles.
The DNA of different species varies a lot. Members of different species will have different genes.
The more related a species is, the more DNA they share.
Genetic diversity within a population is increased by...
- Mutations in the DNA - forming new alleles.
- Different alleles being introduced into a population when individuals from another population migrate into them and reproduce. This is known as gene flow.
A genetic bottleneck is an event that causes a big reduction in a population, e.g. when a large number of organisms within a population die before reproducing.
This reduces the number of different alleles in the gene pool and so reduces genetic diversity.
The survivors reproduce and a larger population is created from a few individuals, but there is reduced genetic diversity.
The founder effect
The founder effect describes what happens when just a few organisms from a population start a new colony.
Only a small number of organisms can contribute their alleles to the gene pool.
There's more inbreeding in the new population, which can lead to a higher incidence of genetic disease.
The founder effect can occur as a result of migration leading to geographical separation, or if a new colony is separated from the original population for another reason, such as religion.
Selective breeding involves choosing which organisms reproduce.
A farmer wants a strain of corn plant that is tall and produces lots of ears, so he breeds a tall strain with one that produces multiple ears.
He selects the offspring that are the tallest and have the most ears, and breeds them together.
The farmer continues this until he produces a very tall strain that produces multiple ears of corn.
Selective breeding leads to a reduction in genetic diversity.
Arguements FOR selective breeding
1. It can produce high-yielding animals and plants.
2. It can be used to produce animals and plants that have increases resistance to disease. This means farmers have to use fewer drugs and pesticides.
3. Animals and plants could be bred to have increased tolerence of bad conditions e.g. drought or cold.
Arguements AGAINST selective breeding
1. It can cause health problems. E.g. dairy cows are often lame and have a short life expectancy because of the extra strain that making and carrying loads of milk puts on their bodies.
2. It reduces genetic diversity, which results in an increased incidence of genetic disease and an increased susceptibility to new diseases because of the lack of alleles in the population.
Good luck on your exams!