Speciation
Speciation
The formation of a new species which results from populations becoming reproductively isolated from one another. With no gene flow occurring speciation may result gradually through a series of small changes, or instantly by changes in chromosome number through polyploidy.
Allopatric Speciation
a type of speciation in which biological populations are physically isolated by an extrinsic barrier and evolve intrinsic (genetic) reproductive isolation, such that if the barrier breaks down, individuals of the population can no longer interbreed.
New Zealands Changing Landscape
The changing geographical landscape of New Zealand has resulted in the production of many new species as a result of allopatric speciation.
Great American Biotic Interchange
Populations of organisms were able to mingle once a land bridge between North and South America arose during the Pliocene, 3.6–2.6 million years ago (mya). Prior to this populations would have been geographically isolated from each other as are species that may be on islands in the oceans on either side of the land bridge.
Allopatric Speciation
The result of some geographical barrier that prevents two populations from breeding together. Overtime due to processes of Evolution (Founder effect, Genetic drift, Mutation and Natural Selection) an accumulation of genetic differences may result in speciation where the two populations will no longer be able to breed even if the geographical barriers no longer exist.
Sympatric Speciation
occurs when two populations of the same species are found in the same territory but are able to split into two different groups and genetically develop so differently that they can no more interbreed and become different species.
Sympatric Speciation
Isolation occurs within the same habitat. Over time the two populations will no longer breed and speciation will become complete.
Reproductive Isolating Mechanisms
(RIM)
Any factor that prevents two organisms of different species from mating and having fertile offspring
Pre-Zygotic Reproductive Isolating Mechanisms
Habitat Isolation
Temporal Isoloation
Mechanical Isolation
Behavioural Isolation
Post-Zygotic Reproductive Isolating Mechanisms
Reduced viability of zygote
Infertility of hybrid offspring
Developmental abnormalities in offspring affecting life expectancy
Pre zygotic and Post Zygotic Mechanisms
Behavioural Isolation
Birds of Paradise each have their own unique courtship rituals.
Aneuploidy
Aneuploidy results from the failure of chromosomes to separate during anaphase of cell division. This is known as non-disjunction. This causes a variation in chromosome number involving only part of the chromosome set. In its most simple form there is only one chromosome involved.
- monosomy - only 1 of a pair is present (2n-1)
- trisomy - three copies of a chromosome are present (2n+1)
- tetrasomy - four copies of a chromosome are present (2n+2)
The significance of this occurrence is dependent on which chromosomes are involved. It is more common in plants than in animals where the effects are almost always harmful.
e.g Trisomy 21 - Downs syndrome
Polyploidy
In polyploidy, every chromosome is represented three or more times so that instead of being diploid(2n) individuals are triploid (3n), tetraploid (4n), hexaploid (6n).
Autopolyploidy is the multiplication of the genome from within a single species.
Alloploidy is hybridisation between species.
Aneuploidy and Polyploidy
Explanation of Aneuploidy and Polyploidy
How Polyploidy leads to Speciation
https://www.pathwayz.org/Tree/Plain/POLYPLOIDY