define natural selection
process by which organisms best suited to their environment survive and reproduce, passing on their characteristics to their offspring through their genes
define gene pool
sum of all the genes in a population at a given time
define allele frequency
relative frequency of a particular allele in a population at a given time
define selection pressure
factors that affect an organisms chance of survival or reproductive success
define selectively neutral allele
does not alter fitness of individual to survive and reproduce
- organisms within species show variation in their characteristics caused by differences in genes. new alleles can arise by mutation
- those with characteristics that are best adapted to a selection pressure have increased chance of survival and successfully reproducing - ‘survival of the fittest’
- successful organisms pass on the allele encoding the advantageous characteristic into offspring
- process repeated for many generations, over time proportion of individuals with adv. adaptation increases -> frequency of adv. allele increases in gene pool
- over very long period of time, can lead to evolution of a new species
explain how natural selection has resulted in the change in frequency of dark and pale moths in populations of the peppered moth near industrial towns and cities over time.
- before industrial revolution, most were pale - camo against tree bark, dark ones were easily spotted and eaten
- during industrial revolution, trees became darker bc covered in soot and loss of lichen cover - dark moths were better adapted bc more highly camouflaged
more + more of them survived and reproduced, increasing frequency of ‘dark’ allele - over time their number became higher than pale due to natural selection - dark color was the advantageous characteristic
after clean air act, trees became paler and number of pale moths increased again
describe how human activity has resulted in evolution in populations of Staphylococcus aureus.
- bacteria reproduce rapidly and evolve in short time
- mutation arose in S. aureus = resistance to methicillin
- when bacteria exposed to antibiotic, resistant individuals survived and reproduced, passing the allele for resistance onto offspring
- non-resistant individuals died
- over time number of resistant individuals increased - establishing MRSA as species
describe how human activity has resulted in evolution in populations of Flavobacterium
- live in waste water of factories that produce nylon 6
- they have evolved to digest nylon - beneficial for cleaning up factory waste
- no other strain of Flavobacterium has nylonases
- thought that gene duplication + frameshift mutation led to this adaptation - was advantageous and so naturally selected bc it provides them with another source of nutrients
define how human activity has resulted in evolution in populations of the Sheep blowfly
- cause fatal condition for sheep - flystrike
- in 1950s, used diazinon pesticide to kill them and prevent the condition
- within 6 years, resistance developed to diazinon - individual insects with resistance survived and passed on advantageous characteristics through alleles, allowing resistant population to evolve
