7.3 Evolution Flashcards
State 3 genetic factors that cause phenotypic variation within a species.
Mutation of alleles
Random fertilisation by gametes
Random assortment of genetic material during meiosis
Why may phenotype vary within a species other than genetic factors?
Environmental influences
Why does natural selection occur?
Factors that change survivial and reproduction
State 3 causes of natural selection.
Predation
Disease
Competition
How does natural selection cause a change in a population’s gene pool over generations?
Organisms with advantageous characteristics are more likely to survive and pass favourable alleles to offspring
Frequency of unfavourable alleles decreases
What is stabilising selection?
Occurs when environmental conditions remain the same
Individuals closest to mean are favoured & new characteristics are selected against
What does stabilising section result in?
Low diversity
What is directional selection?
Occurs when environmental conditions change
Individuals with phenotypes suited to the new conditions will survive and pass on genes
How does directional selection impact a population over time?
The mean of the population to move towards characterstics suited to the environment
What is disruptive selection?
Both extremes of the normal distribution are favoured over the mean
How does disruptive selection impact a population over time?
The population becomes phenotypically divided
Define speciation.
Where a population is split and isolated, there are different selective pressures on the two groups
If the genetic makeup changes to the extent two groups can no longer interbreed, they have become a separate species
What is allopatric speciation?
Speciation resulting from a physical barrier
The environments occupied by the two groups are different and so different alleles are favoured
Give two examples of allopatric speciation.
River
Mountain range
What is sympatic speciation?
Speciation resulting from a non-physical barrier
