3.7.3 Evolution and Speciation Flashcards
what causes a wide range of variations in phenotypes within a species
genetic factors
-mutations
-crossing over
-independent segregation
environmental factors
what is evolution
change in allele frequency over many generations in a population occurring through natural selection
factors that may drive natural selection
predation, disease and competition for survival may lead to differential survival and reproduction
explain the principles of natural selection in the evolution of populations (MARIA)
Random gene Mutations can result in new alleles of a gene
Due to selection pressure, the new allele might benefit its possessor (explain why) leading to a selective Advantage
More likely to survive and have increased reproductivity success
Over many generations allele increases in frequency in the gene pool
Explain the effects of. stabilising selection
Organisms with alleles coding for average variations of a trait have a selective advantage
so frequency of alleles coding for average variations of a trait increase and those coding for extreme variations of a trait decrease
so range and standard deviation is reduced
Explain the effects of directional selection
organism with allele coding for one extreme variation of a trait have a selective advantage
so frequency of alleles coding for this gene increase and frequency of other extreme variations decrease
explain the effects of disruptive selection
organisms with alleles coding for either extreme variation of a trait have a selective advantage
so frequency of alleles coding for both extreme variations of the trait increase and those coding for the average variation of the trait decrease
this can lead to speciation
Describe speciation
reproductive separation of two populations of the same species
This can result in accumulation of differences in their gene pools
new species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring
describe allopatric speciation
population is split due to geographical isolation
this leads to reproductive isolation, separating gene pools by preventing gene flow
random mutations cause genetic variation within each population
different selectional pressures act on each population
so different advantageous alleles are selected for in each population
allele frequencies within each gene pool change over many generations
eventually populations cannot interbreed to produce fertile offspring
Describe sympatric speciation (s=same)
population is not geographically isolated
mutations lead to reproductive isolation , separating gene pools by preventing gene flow
different selectional pressures act on each population
so different advantageous alleles are selected for
so allele frequencies within each gene pool change over many generations
eventually different populations cannot interbreed to produce fertile offspring
explain genetic drift and its importance in small populations
mechanism of evolution where allele frequencies in a population change over generations due to chance
some alleles passed on more/less often due to chance
regardless of selectional pressures and wether alleles give a selective advantage
so strongest effect in small populations with no gene flow with other populations as gene pool is small and chance has a greater influence
this can reduce genetic diversity
what is bottleneck effect
when a population is greatly reduced in size
what is founder effect
when a small, new colony forms from a main population
