Selection And Speciation Flashcards
How does variation arise
Mutation, meiosis,random fertilisation of gametes
Natural selection
Variation exists in a population due to mutation
Selection pressures in environment due to biotic and abiotic factors
Better adapted individuals more lively to survive and reproduce.
More likely to pass on their alleles
Offspring now have advantageous alleles
Increase in allelic frequency over time
Stabilising selection
Occurs in a population where environment is stable
selection pressure at both ends of distribution
Favours the average and eliminates the extreme
Reduces variability
Directional selection
Occurs when population is not extreme
Favours an extreme
Mean will shift towards extreme
Speciation definition
Evolution of a new species from existing species
Two populations must undergo a period of reproductive isolation to become genetically distinct via mutations and selection pressures
allopatric speciation
Physical barrier blocks a population preventing interbreeding
Each population has its own selection pressures and mutations
Change in genotype and phenotype
When populations meet they are so different they can’t interbreed and have become their own species
Sympatric speciation
Become separated by choice
Choice of foods or mates or active hibernation
Become genetically different and develop though selection to become their own species
Genetic drift or bottle neck
Random increase or decrease in allelic frequency
Important in small populations where loss of individuals with certain alleles cause a significant change in the frequency of the alleles within the population
Gene flow or founder effect
Change in allelic frequency due to migration of fertile individuals
Disrupting selection
Opposite to stabilising
Favours both extremes
Over time 2 extremes will dominate and mean will shift in both directions
Least common type
