Effects of selection

Question 1

What does natural selection alter?

Answer 1

the allele frequency in a population

Question 2

What is directional selection?

Answer 2

When individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

Question 3

What could directional selection be a response to?

Answer 3

Environmental change

Question 4

In directional selection, what shifts?

Answer 4

the mean

Question 5

What is an example of directional selection?

Answer 5

bacteria being resistant to antibiotics
the resistant bacteria survive and reproduce without competition, passing on the allele that gives antibiotic resistance to offspring so after time most of the organisms in the population will have the antibiotic resistance allele

Question 6

What is stabilising selection?

Answer 6

When individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce

Question 7

When does stabilising selection occur?

Answer 7

When the environment isn’t changing

Question 8

What does stabilising selection reduce?

Answer 8

The range of possible characteristics

Question 9

What is an example of stabilising selection?

Answer 9

Human baby birth weights
Those who are too big will have complications fitting through the pelvis and this causes problems for the mother and the child
Those who are too small have a high surface area to volume ratio so it is hard to maintain their body temperature, putting pressure on their respiratory and cardiac systems