5. The Effects of Selection Flashcards
What does natural selection alter?
Frequency of allele in population.
What do direction and stabilising selection affect?
Allele frequency in different ways.
Name the 2 types of natural selection.
Stabilising.
Directional.
Define directional selection.
When individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce - in response to environmental change.
EXAMPLE.
Name an example for directional selection.
Some individuals in a bacterial population have alleles that give them resistance to an antibiotic.
EXAMPLE.
What happens when population is exposed to antibiotic?
It kills the bacteria without the resistance allele.
Resistant bacteria survive and reproduce without competition , passing on their allele that gives antibiotic resistance to their offspring.
EXAMPLE.
When the individuals who have passed on their antibiotic resistance allele to their offspring reproduce, what happens?
Most organisms in population will carry antibiotic resistance allele.
What does a graph look like regarding directional selection?
The mean shifts to the right.
(Parents - graph is in normal position, but the grey area signifying breeding population us more to the right side. The offspring - the graph and mean shift to the right)
Define stabilising population.
Where individuals with alleles for characteristics towards the middle of the range are more likely yo survive and reproduce.
Occurring when environment isn’t changing, reducing range if possible characteristics.
EXAMPLE.
Give an example of a stabilising population.
Human birth weight.
EXAMPLE.
What kind of babies will have a lower chance of surviving?
Very small babies - high surface area to volume ratio, meaning they find it hard to maintain body temperature. Putting pressure on their respiratory+cardiac system-fatal.
Very large babies - giving birth to these can be difficult as their size makes it harder for them to fit through mother’s pelvis. Complication for mothers+babies.
EXAMPLE.
What babies are most favourable?
Medium-sized babies.
Weight of humans tends to shift towards the middle of the range.
EXAMPLE.
What is the graph like regarding stabilising selection?
Parents- graph looks normal. Grey segment is in the middle of the graph indicating the breeding population.
Offspring- the graph becomes smaller and remains in the middle.
