Selection

Question 1

What causes selection to occur?

Answer 1

selection pressures

Question 2

What are selection pressures?

Answer 2

environmental factors that limit the size of a population

Question 3

What are 3 examples of selection pressures?

Answer 3

• competition
• predation
• disease

Question 4

What does stabilising selection favour?

Answer 4

average phenotype, against extremes

Question 5

What does directional selection favour?

Answer 5

for one extreme, against another

Question 6

What does disruptive selection?

Answer 6

for the 2 extremes against average

Question 7

What can cause genetic variation?

Answer 7

• mutation
• random fertilisation (crossing over, independent segregation)

Question 8

What could disruptive speciation lead to?

Answer 8

speciation

Question 9

How would large brained females being attracted to bright coloured males be an advantage?

Answer 9

• larger brained females mate with bright-coloured males
• offspring bright in colour
• offspring attract larger brains
• population evolve to have larger brains
• better at spotting and avoiding predators

Question 10

Why would a trait coded for by a dominant allele rapidly increase in frequency once selection is established?

Answer 10

as it is always expressed when present

Question 11

Why might the allele for a late-onset condition not reduce in frequency as a result of selection?

Answer 11

alleles have already been passed on
organisms have already reproduced

Question 12

What are mutations?

Answer 12

RANDOM (or spontaneous) changes in the base sequence of DNA

Question 13

How do environmental factors impact mutations?

Answer 13

rate of mutations increases

Question 14

Why does selection take time?

Answer 14

• mutation/allele is initially very low in frequency
• breeding occurs
• takes many generations for allele to become common

Question 15

Why do allele frequencies differ in 2 populations in different environments?

Answer 15

• different selection pressure
• trait (code for by a specific allele) gives selective advantage
• so more likely to survive and reproduce than other trait
• so change in allele frequency

Question 16

What can be seen in phenotype frequencies over time when selection is occuring?

Answer 16

• would be a clear trend
• as one phenotype would increase chances of survival

Question 17

How could disruptive selection lead to the formation of 2 new species?

Answer 17

• traits coded for by more extreme alleles are favoured
• so these survive, reproduce and pass on alleles
• over time, 2 separate breeding populations
• no longer able to breed (to produce fertile offspring)