Speciation Flashcards
Speciation
The formation of different species from a common ancestor
Species
a group of organisms that can interbreed to produce fertile offspring
Population
a group of organisms of the same species, which live in the same place at the same time
Gene pool
All the inheritable alleles present in a population
First thing needed for speciation to occur
- there must be genetic variation in the original population to begin with
Second thing needed for speciation to occur
- then there must be no gene flow between a group and the original population so that they can change independently
Third thing needed for speciation to occur
- then evolutionary processes must increase the genetic variation between the group and the original population.
Fourth/last thing needed for speciation to occur
- and they must become different enough that RIMs develop so that they can no longer successfully interbreed/produce fertile offspring with the original population
Two types of speciation
Allopatric and Sympatric speciation
Allopatric speciation
The formation of different species due to a geographical barrier separating the original ancestral population into two or more geographically isolated populations
Sympatric speciation
the formation of different species from an ancestral species in the same geographical area without prior geographical isolation (= no geographical barrier involved)
process of allopatric speciation
- Initially a population with genetic variation occupies the same geographical area
process of sympatric speciation
- Initially a population with genetic variation occupies the same geographical area
Sympatric species
species that have previously diverged from a common ancestor and now exist in the same area but remain reproductively isolated (note: can occur via allopatric or sympatric speciation
Allopatric species
species that are geographically isolated
Polyploidy
when an organism has more than two complete sets of chromosomes in its somatic cells e.g. 3n, 4n, etc
What causes polyploidy
caused by non-disjunction during cell division
non-disjuction
chromosomes are not pulled apart correctly during cell division and so causes polyploidy
What is needed to be fertile?
It requires an even number of chromosome SETS and the chromosomes need to be able to form homologous pairs
Allopolyploidy
two different but closely related species contribute chromosomes to a polyploid (if the species were not closely related a hybrid could not form)
Autopolyploidy
one species contributes all the chromosomes in a polyploid.
triploid
when a cell/individual has 3 sets of chromosomes
Diploid
when a cell/individual has 2 sets of chromosomes
haploid
when a cell/individual has half the original number/sets of chromosomes
A way instant speciation and sympatric speciation can occur
when polyploidy results in the formation of hybrid sterility RIM in one generation, so they immediately become separate species
advantages of polyploidy
Polyploidy can produce different phenotypes that might provide a survival advantage and so increase reproductive success for the polyploids
hybrid vigour
individuals that have this often grow larger and faster, and are more robust/resilient e.g. produce more flowers and fruit, or are better able to tolerate harsh conditions
Reproductive Isolating Mechanism (RIM)
any factor that stops organisms from breeding together, so prevents gene flow between groups of organisms (so can result in speciation or keeps species isolated).
Examples of reproductive isolating mechanisms
geographical, ecological, temporal, behavioural, structural barriers, polyploidy
Geographical isolation
when physical barriers (e.g. oceans, mountain ranges, rivers, deserts) separate populations so they cannot come in contact to reproduce and so there is no gene flow
Ecological isolation
individuals of a species live in the same geographical area but occupy different ecological niches to reduce competition and so they rarely come into contact, so they do not reproduce and so there is no gene flow between them.
Temporal isolation
differences in the timing of their behaviour e.g. mating is prevented because the two species breed at different times of the year or day.