10.3 Gene pools and speciation Flashcards
What is a gene pool?
A gene pool represents the sum total of alleles for all genes present in a sexually reproducing population
What does a large gene pool indicate?
High amounts of genetic diversity and increasing the chances of biological fitness and survival
What does a small gene pool indicate?
Low amounts of genetic diversity and reducing biological fitness and increasing chances of extinction
What can gene pools be used to determine?
Allele frequency
What is allele frequency?
The proportion of a particular allele within a population
What does evolution require to happen?
That allele frequencies change within the gene pool of the population to reflect the evolve characteristics
What is evolution?
The cumulative change in the heritable characteristics of a population across successive generations
What are the five processes that can cause changes to allele frequency within a gene pool?
Mutation
Gene flow
Sexual reproduction
Genetic drift
Natural selection
How does mutation result in changes to allele frequency within a gene pool?
A random change in the genetic composition of an organism due to changes in the DNA base sequence
How does gene flow result in changes to allele frequency within a gene pool?
The movement of alleles into or out of a population as a result of immigration or emigration
How does sexual reproduction result in changes to allele frequency within a gene pool?
Sex can introduce new gene combinations and alter allele frequencies if mating is assortative
How does genetic drift result in changes to allele frequency within a gene pool?
The change in the composition of a gene pool as a result of a chance or random event
How does natural selection result in changes to allele frequency within a gene pool?
The change in the composition of a gene pool as a result of differentially selective environmental pressures
What is genetic drift?
The change in the composition of a gene pool as a result of chance or random event
When will genetic drift happen fastest and be most significant and why?
In smaller populations because chance events have a bigger impact on the gene pool
What will be less affected by random events and maintain more stable allele frequencies with low genetic drift?
Larger populations
When will allele frequencies change significantly?
When a large population is reduced to a small population
What are the two mechanisms when a large population is reduced to a small population?
Population bottlenecks and the founder effect
When do population bottlenecks occur?
When an event reduces population size by an order of magnitude
What causes population bottleneck?
Natural occurrences or human induced
What happens to the surviving population of population bottlenecks?
They will have less genetic variability than before and will be at a higher level of experiencing genetic drift
What happens to the surviving species of population bottlenecks when they repopulate?
The newly developing gene pool will be divergent to the original
When does the founder effect occur?
When a small group breaks away from a larger population to colonise a new territory
How does the founder effect differ from population bottlenecks?
The original population remains largely intact
Why is a smaller group in the founder effect subject to more genetic drift?
Because it does not have the same degree of diversity as a larger population
What happens to the smaller group in the founder effect when it increases in size?
Its gene pool will not be representative of the original gene pool anymore
What is the range of allele frequencies?
from 0 - 1.0
What can changes in allele frequencies reflect?
Either random processes or differential processes
When will the population bottlenecks and the founder effect exacerbate genetic differences?
Between geographically isolated populations
How do you compare allele frequencies?
- go to the allele frequency database
- type a gene name into the search parameter
- choose a specific gene loci
- Select a polymorphism
- Choose a frequency display format
What is natural selection?
The change in the composition of a gene pool in response to a differentially selective environmental pressure
What is the frequency of one particular phenotype in relation to another the product of?
The type of selection that is occurring
What is a stabilising selection?
When a middle phenotype is favoured at the expense of both phenotypic extremes
What does stabilising selection result in?
The removal of extreme phenotypes
When does stabilising selection happen?
When environmental conditions are stable and competition is low
What is an example of stabilising selection?
Human birth weights
What is directional selection?
When one phenotypic extreme is selected at the cost of the other phenotypic extreme
What does directional selection result in?
The phenotypic distribution clearly shift in one direction to the beneficial extreme
When does directional selection happen?
In response to gradual or sustained changes in environmental conditions
What is directional selection typically followed by and when?
Stabilising selection once an optimal phenotype has been normalised
What is an example of directional selection?
The development of antibiotic resistance in bacterial populations
What is disruptive selection?
When both phenotypic extremes are favoured at the expense of the middle phenotypic ranges
What does disruptive selection cause?
The phenotypic distribution to deviate from the centre and results in a bimodal spread
When does disruptive selection happen?
When fluctuating environmental conditions favour the presence of two different phenotypes
What may happen if there is a continued separation of phenotypic variants in disruptive selection?
The population may split into two distinct sub populations
What is an example of disruptive selection?
The proliferation of black or white moths in regions of sharply contrasting colour extremes
When does reproductive isolation happen?
When barriers prevent two populations from interbreeding
What are the two main categories of reproductive isolation barriers?
Prezygotic isolation and postzygotic isolation
What is prezygotic isolation?
Occurs before fertilisation can occur so no offspring are produced
What is postzygotic isolation?
Occurs after fertilisation where offspring are either not viable of infertile
What are the different types of prezygotic isolation barriers?
Temporal
Behavioural
Geographical/Ecological
Mechanical
What are the different types of postzygotic isolation barriers?
Inviability
Infertility
breakdown of hybrid organisms
When does temporal isolation occur?
When two populations differ in their periods of activity or reproductive cycles
What is an example of temporal isolation?
Leopard frogs and wood frogs sexually mature at different times in the spring and thus cannot interbreed
When does behavioural isolation occur?
When two populations exhibit different specific courtship patterns
What is an example of behavioural isolation?
Certain populations of cricket may be physically the same but only respond to specific mating songs
When does geographic isolation occur?
When two populations occupy different habitats or separate niches within a common region
What is an example of geographic isolation?
Lions and tigers occupy different habitats and do not interbreed
What is hybrid inviability?
When hybrids are produced but fail to develop to reproductive maturity
What is hybrid infertility?
Hybrids fail to produce functional gametes
What is hybrid breakdown?
F1 hybrids are fertile but F2 generation fails to develop properly
What is speciation?
An evolutionary process that results in the formation of a new species from a pre existing species
When does speciation occur?
When reproductive isolating mechanisms prevent two breeding organisms from producing fertile viable offspring
What are the two ways speciation can occur?
Allopatric and sympatric speciation
When does allopatric speciation occur?
When a geographical barrier physically isolates populations of an ancestral species
What are the reasons two populations begin to evolve in allopatric speciation?
Cumulative mutation
Genetic drift
Natural selection
What eventually happens in allopatric speciation?
The two populations reach a degree of genetic divergence where they can no longer interbreed
What is sympatric speciation?
The divergence of species within the same geographical location
What can cause sympatric speciation?
The reproductive isolation of two populations as a result of genetic abnormalities
What error typically arises during sympatric speciation and what does that cause?
A chromosomal error may arise which prevents successful reproduction with any organism lacking the same error
Structurally, what can cause speciation?
A meiotic failure during gamete formation
What happens if meiotic cells fail to undergo cytokinesis?
Chromosomal number will double in the gamete
What is the result of offspring where the chromosomal number is double in the gamete?
Offspring with additional sets of chromosomes
How can polyploid offspring cause speciation?
If the offspring are viable and fertile but cannot interbreed with the original parent population
What do fertile polyploid offspring typically require?
Two polyploid parents
Why do fertile polyploid offspring need two polyploid parents?
Because reproduction with an the original parent population results in offspring with an uneven number of chromosome sets
Where is polyploidy more common and why?
Plant species as they lack separate sexes and can reproduce asexually
Can infertile polyploids still reproduce asexually?
Yes via vegetative propagation
Why do farmers develop polyploid crops? (two reasons)
Allows for the production of seedless fruits
Polyploid crops grow larger and demonstrate improved longevity and disease resistance
How can farmers induce polyploidy in certain plant species?
By treating plants with certain drugs
What is the genus allium comprised of?
Monocotyledonous flowering plants like onions, garlic, chives and leeks
What has happened in the allium species?
Polyploidy resulting in reproductively isolated populations with distinct phenotypes
What are the two ways evolution can occur?
Microevolution and macroevolution
What is microevolution?
Within a species
What is macroevolution?
Across the species barrier
What are the two ways evolution via speciation may occur?
Phyletic gradualism or punctuated equilibrium
What is the phyletic gradualism model?
Speciation occurs uniformly via the steady and gradual transformation of whole lineages
What supports phyletic gradualism?
The fossil record of the horse as many middle forms connect to the modern equivalent
In accordance to phyletic gradualism what type of process is speciation viewed as?
A smooth and continuous process
What is the punctuated equilibrium model?
Species remain stable for long periods before undergoing abrupt and rapid change
What type of process is speciation according to punctuated equilibrium?
A periodic process where big changes happen suddenly followed by long periods of no change
What evidence supports the punctuated equilibrium model?
The general lack of transitional fossils for most species
Apart from punctuated equilibrium what else can explain the lack of traditional fossils?
The rare and irregular conditions needed for fossilisation
