Speciation Flashcards
Define speciation
The formation of a new species
Define hybridisation
The production of offspring as result of sexual reproduction between individual from two different species
Define allopatric speciation
Speciation that occur when population are physically or geographically separated and there can be no interbreeding or gene flow between the population
- geographical separation
- prevent breeding
- different habitat
- evolve adapt
The proportion of different genotype in each population changes independantly of each other
—> individuals develop adaptation according to their local conditions
Over time, the oopulation may become so genetically different that they are unable to interbreed to produce fertile offspring - separate specie
Sympatric speciation
Speciation that occurs between population of a species in the same place; they become reproductively separate by mechanical, behavioural or seasonal mechanism; gene flow continues between the population to some extent as speciation occurs.
Reproductive separation
Biochemical change
Physical change
Define founder effect
The loss of genetic variation that occurs when a small number of individual become isolated, forming a new population with allele frequencies not representative of the original population
Define population bottleneck
The effect of an event or series or series of events that dramatically reduces the size of a population , resulting resulting in large changes in allele frequencies and a reduction in genetic diversity
Define genetic drift
Change in allele frequncy within a population between generation
Happens to all population
Has drastic effwct in amall poplation
Driven by chance ,not selection
Properties of genetic drift
Happens to all population
Has drastic effect in small population
Driven by chance, not selection
Two main types: founder effect and bottleneck effect
Define selection pressure
The effect of one or more environmental factors that determine whther an organism will be more or less sucessful at surviving and reproducing: selection pressure drives speciation
What cause selection pressure
-disease
-competition
—> food
-predation
Propterties of allopatric speciation
1) separated population unable to reproduce to the physical barrier
2) the separated population have different environment/selection pressure, so will accumulate different beneficial mutation over time to help them survive. This leads to differential reproductive success so change in allele frequncy
4) the two population eventually become so geentically different that they cant reproduce to produce fertile offspring (reproductive isolation) so are classed as different species
Properties of sympatric speciation
Random mutation could interfere reproductiove behavior eg individual fertile at different times of year or different courtship behaviour
Individual will not reproduce togther
Over time, their DNA becomes so different so individual are no longer able to reproduce to produce fertile offspring , so are closed as 2 different species
Geographical isolation
By a physical barrier such as river
Ecological isolation
Two population inhabit the same region, but develop preferences for different parts of the habitat
Seasonal isolation
The timing for flowering or sexual receptiveness differs for two different species
Occurs when the breeding season of two population dont coincide
Over time the population may become so genetically different that they are unable to interbreed to produce fertile offspring
—> separate specie created
Steps for allopatric speciation
1] new habitat due to separation
2) different selection pressures
3) different allele selected
Those with the allele are more likely ro survive and reproduce
4) change in allele frequency in the gene pool
5) characteristic are accumulated until a new specie is formed
Properties of sympathic speciation
—> occurs within same habitat
-mating preference, disruptive selection
Natural selection process
Random mutation give rise to new allele
Each species reproduces and offspring show variation
Due to selection pressure(there is a lot of competitions between these offspring) from environement individuals with beneficial allele are more likely to survive and reproduce and pass on their advantageous allele
This process repeats over mant generation
The frequency of the advantageous allele therefore increase in the population
Evolution definition
The formation of new species from pre-existing species over time, as a result of changes to gene pools and allele frequencies from generation to generation
Allopatric process
This creates two populations of the same species who are reproductively separated from each other, and as a result, no genetic exchange can occur between them
If there are sufficient selection pressures acting to change the gene pools (and allele frequencies) within both populations then eventually these populations will diverge and form separate species
The changes in the alleles/genes of each population will affect the phenotypes present in both populations
Over time, the two populations may begin to differ physiologically, behaviourally and morphologically (structurally)
Sympatric process
Sympatric speciation takes place with no geographical barrier
A group of the same species could be living in the same place but in order for speciation to take place there must exist two populations within that group and no gene flow occurs between them
Something has to happen that splits or separates the two populations:
Ecological separation: Populations are separated because they live in different environments within the same area
For example, soil pH can differ greatly in different areas. Soil pH has a major effect on plant growth and flowering, so a population growing in soil with a slightly different pH may flower at a different time from another population, leading to reproductive separation (and eventually genetic isolation) of the two populations
Behavioural separation: Populations are separated because they have different behaviours
For example differences in feeding, communication or social behaviours, such as courting behaviours to attract a mate
Example of sympatric
A species of fish lives in a lake
Some individuals within the population feed on the bottom while others remain higher up in the open water
The different feeding behaviours separates the population into different environments
Here, behavioural separation has led to ecological separation
The separated groups experience different selection pressures
Long jaws are advantageous for bottom-feeding whereas shorter jaws are advantageous for mid-water feeding
Over time natural selection causes the populations to diverge and evolve different courtship displays
They can no longer interbreed; they are now considered separate species
Genetic drift
In geographically isolated populations, differences in selection pressures can lead to changes in allele frequencies, and eventually to speciation due to evolution via natural selection
However, evolution can also occur via genetic drift
This is when chance (instead of environmental selection pressures) affects which individuals in a population survive, breed and pass on their alleles
For example, when a population is significantly small, chance can affect which alleles get passed onto the next generation
Over time, some alleles can be lost or favoured purely by chance
When there is a gradual change in allele frequencies in a small population due to chance and not natural selection, genetic drift is occurring
In large populations, genetic drift is less likely to have an effect because any chance variations in allele frequencies usually even out across the whole population
Natural selection has a much more influential role in the evolution of large populations
Genetic drift
When a population is significantly small, chance can affect which alleles get passed onto the next generation
Over time some alleles can be lost or favoured purely by chance
When there is a gradual change in allele frequencies in a small population due to chance and not natural selection then genetic drift is occurring
Founder effect
The Founder effect occurs when only a small number of individuals from a large parent population start a new population
As the new population is made up of only a few individuals from the original population only some of the total alleles from the parent population will be present
In other words, not all of the gene pool is present in the smaller population
A gene pool is the complete range of DNA sequences (alleles) that exist in all the individuals of a population or species
Which alleles end up in the new founding population is completely up to chance
As a result, the changes in allele frequencies may occur in a different direction for the new small population vs the larger parent population
Bottleneck effect
It occurs when a previously large population suffers a dramatic fall in numbers
A major environmental event can massively reduce the number of individuals in a population which in turn reduces the genetic diversity in the population as alleles are lost
The surviving individuals end up breeding and reproducing with close relatives
Result of natural selection
Selection pressure produce a gradual change in allele frequencies over several generation
Result of founder effect
Changes in allele frequencies occur in a different directiob for a newly isloated small popullation in comparison to the larger parent population due to chance
Genetic drift results
Gradual change in allele frequencies in a small population due to chance and not natural selection
Bottleneck effect result in
Reduction in the gene pool of a population due to a dramatic decrease in population size
Genetic bottleneck
When an event or series of events drastically reduced the size of the population through the death of many organism
-severe decrease in the gene pool of the population
-many of the gene variant present in the original population are lost
—> so the gene pool shrink and the allele frequency shrink
Genetic diversity is reduced
Founder effect
Loss of genetic variation that occurs in small number of individuals that leaves the main population and set up a new population producing voluntary ‘population bottlenecks’.
The allele carried by the individual who leave the main population may be a random selection of the gene pool but is unlikely will include all the allele or same frequency as in the original population
Allopathic speciation
geographical isolation
- population of species split and move to different areas
- each new population experiences different selective pressures –> features change over time, mutations occur
- when the different populations are reintroduced, they can no longer interbreed
- -> new species have evolved
Sympatric speciation
- ecological and behavioural separation
- sympatric speciation usually occurs through polyploidy
polyploidy organism: has more than 2 complete sets of chromosomes
happens when meiosis goes wrong when forming gametes
tetraploidy: 2+2 = 4; tetraploids are often sterile as 4 sets of chromosomes try to pair up during Meioisis I and get muddled up –> can reproduce asexually; usually happens in plants
triploidy: 1+2 = 3; triploidy are always sterile as 3 sets of chromosomes can not be shared evenly between daughter cells
the original diploid plant and tetraploid plant can no longer interbreed –> new species formed
Evidence for evolution Fossil
Shows gradual changes
Shows intermediate
Can be dated
Evidence for evolution
Changes in base sequence
Evidence for evolution
Proteins
Cytochrome
