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Flashcards in Populations and Evolution Deck (15):

Definition of a species?

A group of similar organisms that can reproduce to give fertile offspring


Definition of a population?

A group of organisms of the same specie living in a particular area at a particular time - with the potential to interbreed


Definition of the gene pool?

All the alleles present in a population


Definition of allele frequency?

How often an allele occurs in a population


Hardy-Weinberg conditions?

Large population
No immigration or emigration
No mutations or natural selection
Has to be random mating


What is evolution?

The change in allele frequencies over time


Process of evolution?

Predation, disease and competition act as selection pressures
Some members of population have different alleles which make them better adapted for survival
Different levels of survival and reproductive success in a population
Those who survive are more likely to reproduce and pass on their alleles
The offspring then have a better chance of survival and reproduction
Over generations the frequency of the beneficial alleles increases


What is stabilising selection?

Individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
Occurs when environment is not changing and reduces number of possible phenotypes
Baby weights


What is directional selection?

Individuals with alleles for a single extreme phenotype are more likely to survive and reproduce
Change based off of environmental change
Dem moths


What is disruptive selection?

Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce.
When environment favours more than one phenotype
Beak sizes


What is speciation?

The development of a new species
Due to populations of the same species becoming reproductively isolated - changes in allele frequency cause change in phenotype - no longer interbreed - no more fertile offspring


Types of speciation?

Allopatric - Physical barrier - geographical isolation
Sympatric - same place reproductive isolation


Process of allopatric speciation?

Geographical isolation
Gene pools separated
Different environmental conditions
Different selection pressures
Selection pressures causes differential reproductive success as some alleles favour survival than others
Changes in two populations phenotypes
Also mutations
Wont be able to interbreed to produce fertile offspring
Reproductively isolated


Other ways of reproductive isolation?

Seasonal mating - different flowering or mating seasons changes when populations are sexually active
Mechanical - changes in genitalia
Behavioural - courtship rituals - are not attractive to main population


Speciation from Genetic Drift?

Chance causes differential survival and therefore reproduction
Has a greater effect on smaller populations where chance has a smaller effect
By chance a certain allele is passed on more often than others