7. the origin of species Flashcards
true or false:
-mutations always have a negative effect
false
sometimes mutations don’t even have an effect
define gene flow
the movement of genes between populations
give an example of gene flow
bees & flowers:
bees and other insects transfer gametes from one population to another
define genetic drift
chance alterations in a populations allele frequency
what are the two causes of genetic drift
founder effect
genetic bottleneck
what is genetic bottleneck
an event led to only a few individuals surviving, significantly reducing variation in the gene pool
what is founder effect
colonisation of a new large area, eg Galapagos. the few individuals become the founders of a new isolated population
give an example of where founder effect has had negative impact
dutch migrated to South Africa, these individuals had high frequency of alleles for Huntington’s disease, these alleles became prominent in the population
what are the three modes of natural selection
stabilising selection
directional selection
diversifying selection
describe stabilising selection
favours average, extremes are disadvantaged
describe directional selection
one side of outliers Is favoured
describe diversifying selection
extremes are advantaged. average is disadvantaged
why does selection occur at high density populations
adaptations are favoured that enable reproduction with fewer resources
why does selection occur at low density populations
selection favours traits that promote rapid reproduction
what are the two types of speciation
allopatric
sympatric
define allopatric speciation
this is where a population forms a new species whilst geographically separated from its parent population
some alleles may be lost
define sympatric speciation
occurs in geographically overlapping populations
gene flow is reduced
what are the two types of reproductive barriers
pre-zygotic
post-zygotic
what is pre-zygotic
impeded mating or fertilisation of ova
what is post-zygotic
prevents an ovum fertilised by another species from developing into a viable fertile adult
give an example of prezygotic
habitat isolation
mechanical- not physically possible
what are the two theories for rates of evolution
gradualism
punctuated equilibrium
what is gradualism
gradual evolutionary change- slow but constant over long periods of time
what is punctuated equilibrium theory
appearance of new characteristics give rise to new species quickly- then stay the same for a long time
(equilibrium)
