Species = a group of similar organisms which can interbreed to produce fertile offspring.
Speciation = the evolution of a new species from an existing one.
Speciation can occur in two different ways:
- Cross fertilisation may occur between two different species producing a fertile hybrid (eg. the grass species Spartina anglica)
- Isolation of groups of the same species so they can no longer interbreed (reproductive isolation)
Reproductive isolation = when groups within the population become isolated from each other and can no longer interbreed.
Gene pool = all the genetic information present within a population within a given time.
When reproductive isolation occurs, gene flow is prevented between the separate groups, so the population's gene pool is split into several different gene pools.
Allele frequency = the number of times an allele occurs within the gene pool.
Phenotype = characteristics of an organism resulting from it's alleles
Allele frequencies within each pool may now change because the groups may have different selection pressures acting upon the phenotypes of the organisms.
The separate groups may become so different from each other…