speciation + artificial selection Flashcards
What is speciation? (2)
The process by which new species arise from existing species,
Two main types: Allopatric and Sympatric speciation
What is allopatric speciation driven by? (1)
Geographical isolation
What are the steps of allopatric speciation? (5)
- Start with a population with variation,
- Population gets geographically isolated into groups,
- Each group faces different environments or selection pressures,
- Each group undergoes different directional selection,
- Groups change so much genetically that they cannot interbreed to produce fertile offspring = new species
What is sympatric speciation? (2)
Speciation occurring in the same geographical area,
Driven by random mutation
How does reproductive isolation occur in sympatric speciation? (4)
Temporal mechanism: Different breeding seasons.
Behavioural mechanism: Different courtship behaviours, -
Mechanical mechanism: Mismatch of reproductive parts,
Hybrid sterility: Individuals with different numbers of chromosomes can’t reproduce sexually to produce fertile offspring
What happens to the gene pool and selection pressures in sympatric speciation? (3)
- As the two populations are reproductively isolated, there is no gene flow between them,
- Each population experiences different selection pressures,
- The gene pools diverge due to the different environments
What is artificial selection? (1)
The selection of individuals for breeding with desirable characteristics
How is artificial selection used in modern dairy cattle? (4)
Farmers select a female with a very high milk yield and a male whose mother had a very high milk yield,
They breed the two together,
Offspring with the highest milk yields are bred over several generations,
Produces cattle with very high milk yields
How is artificial selection used in bread wheat? (3)
Wheat plants with a high wheat yield are bred together,
Offspring with the highest yields are bred over several generations,
Produces plants with very high yield
What are the ethical considerations of artificial selection in terms of the gene pool? (3)
Artificial selection reduces the gene pool,
Only organisms with similar traits and similar alleles are bred together,
Leads to a reduction in the number of alleles in the gene pool
What are the future problems of a reduced gene pool due to artificial selection? (3)
A reduced gene pool can lead to future problems,
If a new disease appears, there is less chance that any of the alleles will offer resistance,
Potentially useful alleles may be lost when other alleles are selected for
