10.3 Speciation Flashcards
Define speciation
SPECIATION: an evolutionary process which results in new species evolving from pre-existing species
(reproductive isolation is created)
Mechanisms of speciation
- Allopatric: due to geographical separation
- Sympatric: reproductive isolation
Explain allopatric speciation
Due to geographical barrier - physically isolates populations - evolve separately - cumulative mutation, genetic drift, natural selection - can no longer interbreed - distinct species (speciation)
Explain sympatric speciation
In same geographical location but reproductive isolation (genetic abnormalities - different species - interbread between abnormal - speciation)
Chromosomal error: polyploidy - viable but infertile or viable and fertile with other polyploids of the same mutation
Define gene pool
GENE POOL: sum of all alleles in all genes in a sexually reproducing population
Define evolution
EVOLUTION: cumulative change in the heritable characteristics of a population in successive generations
Changes in allele frequencies in gene pools
Mechanisms of evolution
Changes in allele frequencies in gene pools due to:
- mutations: random change
- gene flow: immigration/emigration - movement of alleles
- sexual reproduction: ne geen combinations, change allele frequencies
- genetic drift: change in composition of a gene pool - chance or random event (ex kill have of population)
- natural selection: differentially selective environmental pressures
Define genetic drift
GENETIC DRIFT: chnage of a composition of a gene pool due to chance or random event
Faster and more impactful in small populations
Larger population - more stable allele frequencies
Explain population bottlenecks
Botlenecks occur when a population experiences a reduction by more than 50%
Causes:
- natural disatsers (fires, floods)
- human induced (overhunting)
Remaining population smaller - more prone to genetic drift - new gene pool will be created
Explain founder effect
The founder effect occurs when a small population breaks apart from a larger population colonising new land - more genetic dirft (more diverse the small group) - as it grows no longer representation of original population
Different from bottleneck - the original population remains
Types of selection
- stabilising: intermediate is favourable, environmental conditions are stable (ex human birth weights)
- directional: one phenotypic extreme is favourable, gradual change in environmental conditions, stabilising selection after directional completed (ex antibiotic resistance)
- disruptive: both phenotypic extremes are favourable but not intermediate, fluctuating environmental conditions, eventually split into two sub-populations (ex black and white months in different carbon emission areas)
Define natural selection
NATURAL SELECTION: change in the composition of a gene pool in response to differentially effective environmental pressure
Define reproductive isolation
REPRODUCTIVE ISOLATION: when barriers prevent two populations from interbreeding - separate gene pools
Categories:
- prezygotic: before fertilisation - no offspring
- postzygotic: after fertilisation - non viable/fertile offspring
Types of prezygotic and post-zygotic reproductive isolation
Microevolution vs macroevolution
Microevolution - within a species
Macroevolution - across species barrier
Phyletic gradualism vs punctuated equilibrium
Phyletic gradualism: continuous linage ina acharacteristic
Graduated equilibrium: stable for long time - rapid change
Explain phyletic gradualism
PHYLETIC GRADUALISM
speciation smooth and continuous process
Supported by fossil records of horse
Explain punctuated equilibrium
PUNCTUATED EQUILIBRIUM
speciation is aperiodic process - sudden chnages after stable periods
Lack of transition fossils
