KA7- Evolution Flashcards
What is evolution?
The process of gradual change in the characteristics of a population of organisms over time.
What does evolution link?
Existing species with extinct ancestors
Why are individuals in a population varied?
Due to differences in their genomes
Who presented the theory suggesting that the main driving force for evolutionary change is natural selection?
Charles Darwin and Alfred Wallace
When was the theory of natural selection presented?
1858
Why will certain individuals possess genetic sequences that give them an advantage over others?
Variation
What is natural selection?
The non-random process that increases the frequency of these sequences in the population, by favouring individuals that have them
Explain the steps of natural selection
1) Best suited organisms survive and breed
2) These offspring have an advantage because their parents have passed in their advantageous alleles
3) Organisms who inherit the best combinations of these genes controlling certain characteristics are more likely to survive, breed and pass on their beneficial alleles
4) The other organisms will die before they can pass on their alleles
What do deleterious sequences code for?
An inferior characteristic which leaves an individual poorly adapted to its environment
What controls many traits/characteristics?
Several interacting genes (polygenes)
What happens to the poorly adapted individual.
These individuals usually fail to breed, pass on fewer copies of the sequence and will become reduced in frequency or may even disappear
What do polygenes show?
Continuous variation, across a normal distribution
What happens in stabilising selection?
Intermediate phenotypes are favoured and extremes are selected against
When is directional selection common?
During a period of environmental change
What do selection pressures result in?
The population becoming split into two distinct groups
