Option D2: Species and Speciation

Allele Frequency: Proportion of a gene that makes up a population. The number of allele copies in a population. (eg. if the allele frequency is 25% for a certain population, then one fourth of the population will have that allele while the other three fourths will have a different variant(s) of the gene.

Gene Pool: All possible allele variants of a gene found within a population.
Restrictions to a gene pool can either be made before fertilisation occurs (preygotic isolation) or after fertilization occurs (postzygotic isolation):

Pre-Zygotic Isolating Types
Temporal Isolation	Two species mate/flower at varying times of the year
Ecological Isolation	Two species occupy different habitats with similar regions
Behavioural Isolation	Two species exhibit different mating patters
Mechanical Isolation	Two species are physically impossible to mate
Post-Zygotic Isolating Types
Hybrid Unviability	Hybrids are born but unable to reach sexual maturity
Hybrid Infertility	The hybrid cannot produce functional sex cells
Hybrid Breakdown	The second generation of hybrids are infertile or don’t develop

Evolution will produce a change in the allele frequency towards the allele that produces the more favourable traits. Traits that are favourable will be passed on to the offsping, but this might require many generations before a noticeable change is found

Species: group of organisms capable of interbreeding. Hybrids are formed when two different species are cross bred
Speciation: creation of new species from an existing species. There are times when speciation occurs and a new species is found. This can happen when members of a species are separated geographically or genetically and new characteristics are needed to survive/thrive.
Allopatric Speciation: New species is formed due to geographical barrier that separates the species' population
Sympatric Speciation: New species formed in the same geographical area, but the genes diverge through reproduction

Polypoidy: Some organisms can have more than two pairs of chromosomes. This is usually found in plants and uncommon in animals as plants are capable of asexual reproduction and lack 'sexes'. This can be a result of an error during meiosis or cell division. Offspring instantly becomes a new species, mostly incapable of breeding with the original species

Adaptive Radiation: is the genetic change experienved by a population of a species due to varying habitats and it's the environmental pressures. The result is speciation from one lineage.
Divergent and Convergent evolution are subtopics to adaptive radiation in which divergent evolution experiences a change in their appearance that is different from the original species. Over time species will become more and more different than the original. Convergent evolution is merely the opposite to divergent evolution where their appearance will be more and more alike even though they are different species or have different ancestors. This can be caused by similar habitats that might require certain traits in order to survive.