Speciation Flashcards
Speciation
Evolution of new species from an existing species (common ancestor)
What leads to evolution of new species?
Changes in allele frequency in a population, either by:
alleles with selected advantage increase in population (natural selection)
Random changes in allele frequency by genetic drift
What 2 steps of speciation are there
Reproductive separation
Arise of new species that CANT interbreed to give fertile offspring
What is reproductive separation
Separation of 2 populations of the same original species so 2 species cannot breed together and hence accumulate relative different frequencies of alleles in gene pool
Because they are geographically isolated
2 types of speciation
Allopatric
Sympatric
Allopatric speciation
When an original population became 2 different populations due to geographic isolation
Which eventually lead to 2 new species to arise
Examples of geographic isolation
Formation of sea between populations, rivers, mountains
3 Steps of allopatric speciation
Geographic isolation of 2 populations of an original species leading to reproductive isolation
Natural selection occurs within each population = evolution
Formation of new species that cant interbreed to give fertile offspring
Allopatric speciation: geographic isolation
Two populations of the same species end up in different habitats that are geographically isolated from each other
The geographical isolation causes reproductive isolation since the two populations are physically separated (no gene flow between populations/gene pools remain separate)
Allopatric speciation: Natural selection within 2 isolated populations and lack of gene flow
Mutations cause differences in ____ that lead to ____
so further reproductive isolation between 2 populations
There are different selection pressures in different habitats;
Different alleles are selected for and passed on in each population, leading to a change in the frequency of the alleles (EVOLUTION)
Allopatric speciation: 2 different species arisen from original population
Eventually the different populations cannot interbreed to produce fertile offspring (even if they came back together): they have become two different species
What is reproductive isolation?
Becomes biologically impossible for 2 species to be bred together to give a fertile offspring
Examples of reproductive isolation
Gametes of 2 species cannot fuse together
Fertilisation cannot occur due to not homologous chromosomes
Cannot identify a mate to reproduce with due to courtship differences
Is reproductive isolation present in both allopatric and sympatric speciation?
Yes
Sympatric speciation
New species form from the same original population in the same habitat (no geographical isolation)
Steps of sympatric speciation
NO geographic isolation but reproductive isolation occurs
Due to mutation and natural selection and lack of gene flow resulting in changes in allele frequency
So eventually forms new species
Sympatric speciation: no geographic isolation
No geographic isolation so speciation Occurs in a population all in the same habitat with no geographical isolation (but probably in different niches of that habitat);
Sympatric speciation: natural selection and lack of gene flow in both populations
Mutations cause differences in _____that lead to ____
thus reproductive isolation (no gene flow/gene pools remain separate)
Different alleles are selected for and passed on in each population, leading to a change in the frequency of the alleles
Sympatric speciation: formation of different species
Eventually the different populations cannot interbreed to produce fertile offspring: they have become two different species
(probably an example of disruptive selection)
Interbreed
Breed together
Inbreed
Breed together very closely related organisms eg siblings
