Types of Selection Flashcards
What is directional selection?
Selection that favours individuals that vary in one direction from the mean, changing the characteristics of the population
What is stabilising selection?
Selection that favours average individuals and preserves the characteristics of a population
What are most characteristics influenced by?
More than one gene - they are polygenic.
How does the environment affect these characteristics?
It causes individuals to vary about the mean
How do directional and stabilising selection affect the normal distribution curve?
Directional selection shifts the curve to one side; stabilising selection narrows the curve around the mean (CHECK BOOK FOR REFERENCE)
What triggers directional selection in a population?
A change in environmental conditions
In directional selection, which individuals are favoured?
Individuals with phenotypes best suited to the new conditions, falling to either the left or right of the mean
What happens to the mean phenotype during directional selection?
It shifts in the direction of the favoured individuals over time
What does directional selection do to a population’s normal distribution curve?
It shifts the curve towards the side of the advantageous phenotype
When does stabilising selection occur?
When environmental conditions remain stable
In stabilising selection, which individuals are favoured?
Individuals with phenotypes closest to the mean
What happens to individuals with extreme phenotypes during stabilising selection?
They are selected against and less likely to pass on their alleles
What does stabilising selection do to the normal distribution curve?
It narrows the curve around the mean, reducing variation
What are the three types of adaptations that natural selection can result in?
Anatomical, physiological and behavioural adaptations
What is an anatomical adaptation, give an example
An anatomical adaptation is the change in structural features, for example: shorter ears, thicker fur, beak shape
What is a physiological adaptation
A physiological adaptation is when different enzymes/chemicals within the animal/human body are formed
What is a behavioural adaptation, give an example
A behavioural adaptation is a change in the behaviour of an organism, for example: animals migrating or penguins huddling for warmth
