Topic 7B - Populations And Evolution Flashcards
What is intraspecific variation
Variation within a species means individuals within a population show a wide range of different phenotypes.
What is evolution
The frequency of an allele in a population changes overtime
What are the 3 types of selection
Stabilising
Directional
Disruptive
What is stabilising selection?
Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
When does stabilising selection occur and what dies it result in?
Occurs when the environment isn’t changing
Reduces the range of possible phenotypes
What is directional selection?
Where individuals with alleles for a single EXTREME phenotype are more likely to survive and reproduce
When would directional selection occur?
In response to a change in the environment
What is disruptive selection?
Where individuals with alleles for extreme phenotypes are more likely to survive and reproduce
When is disruptive selection most likely to occur?
When the environment favours more than one phenotype
What is reproductive isolation?
When changes occur in allelic frequency which cause changes in phenotypes, which means they can no longer interbreed to produce fertile offspring
What is allopatric speciation?
No gene flow between the two populations
What is sympatric speciation?
When a population can becomes reproductively isolated without any physical separation
What are the mechanisms of reproductive isolation? (3)
Seasonal changes
Mechanical changes
Behavioural changes
What is seasonal changes? (Reproductive isolation)
Individuals develop different flowering or mating seasons, or become sexually active at different times of the year.
What are mechanical changes? (Reproductive isolation)
Changes in the size, shape or function of their genitals preventing individuals from breeding
