18 populations and evolution Flashcards
what are the causes of variation in sexual reproduction?
mutation
meiosis
random fertilisation/fusion of gametes
what is a mutation?
sudden change in base sequence of DNA
any mutation could:
- confer a selective advantage
- be neutral
- confer a selective disadvantage
how does the environment cause variation in phenotypes?
- climatic conditions
- abiotic factors
- biotic factors
give an example of an abiotic factor
temperature
light intensity
soil pH
etc
give an example of biotic factors
predators
food supply
what kind of characteristics form a normal distribution curve?
characteristics that are polygenic
what does a normal distribution curve look like?
bell shaped
define selection
process where organisms that are better adapted to the environment survive and reproduce in greater numbers resulting in the increase of the frequency of advantageous alleles within the population
what are the 4 types of selection?
stabilising
natural
directional
disruptive
when does natural selection occur?
when variation exists
describe natural selection
better adapted individuals more likely to survive and reproduce to pass on alleles
less well adapted individuals less likely to survive and reproduce to pass on alleles
organisms subject to selection pressure
what does selection pressure do?
determines the spread of alleles within a gene pool
when does stabilising selection occur?
when the environment is stable
describe selection pressure
selection pressure at both ends of the distribution
favours the average and reduces variability
when does directional selection occur?
when individuals one side of the mean survive better or reproduce more than those on the other
describe directional selection
environmental change produces a new selection pressure which favours a new extreme
mean phenotype shifts
when does disruptive selection occur?
when individuals of a mean phenotype are less fit than those of both higher and lower phenotype
describe disruptive selection
opposite of stabilising
selection pressure favours 2 extremes and they dominate so the mean shifts to opposite ends
define the term genetic drift
the random change in allelic frequency
when is genetic drift important and why?
in small populations
loss of individuals with certain alleles results in a significant change in allelic frequency
define the term gene flow
change in allele frequency due to the migration of fertile individuals
give an example of genetic drift
volcano eruption
tsunami
earthquake
give an example of gene flow
migration
