Selection Flashcards
What causes selection to occur?
selection pressures
What are selection pressures?
environmental factors that limit the size of a population
What are 3 examples of selection pressures?
- competition
- predation
- disease
What does stabilising selection favour?
average phenotype, against extremes
What does directional selection favour?
for one extreme, against another
What does disruptive selection?
for the 2 extremes against average
What can cause genetic variation?
- mutation
- random fertilisation (crossing over, independent segregation)
What could disruptive speciation lead to?
speciation
How would large brained females being attracted to bright coloured males be an advantage?
- 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
Why would a trait coded for by a dominant allele rapidly increase in frequency once selection is established?
as it is always expressed when present
Why might the allele for a late-onset condition not reduce in frequency as a result of selection?
alleles have already been passed on
organisms have already reproduced
What are mutations?
RANDOM (or spontaneous) changes in the base sequence of DNA
How do environmental factors impact mutations?
rate of mutations increases
Why does selection take time?
- mutation/allele is initially very low in frequency
- breeding occurs
- takes many generations for allele to become common
Why do allele frequencies differ in 2 populations in different environments?
- 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
