Phylogenetic Tree:represents evolutionary relationships with common ancestry
branch population through time
direction of branches is the direction of time
node / fork a point in time when an ancestral species slip into descendant
tip / terminal node species that is living today or went extinct
monophyletic group cut a branch, all attached is part of the group
Microevolution: changing allele frequency
Evolution is a process that happens to populations. It doesn't happen to individuals because
individuals are given a set of DNAthat does not change. DNAsequence can only change when
offspring a born so evolution happens between generations. Many individuals that are born
reproduce and die allow change in allele frequency to occur.
Variation is important for evolution so that the allele frequency can change. (if there is only one
allele it will always remain and nothing will change). Variation is generated by mutation. (When
looking at a graph/scenario: The more alleles, and the more evenly distributed those alleles are
the more variation)
p^2 + 2pq + q^2 = 1 p^2 = genotype frequency of Homozygous
q^2 = genotype frequency of Homozygous
(adds up frequency of all 2pq = genotype frequency of Heterozygous
(phenotype frequency, if p is Dominant and q is recessive...
p^2 + 2pq = Dominant phenotype frequency
q^2 = recessive phenotype frequency
p + q = 1 p = allele frequency
q = allele frequency
(adds up frequency of all
Be careful if it says EGG or SPERM they only have one allele! so the chance of those having an
allele is ‘p’or ‘q’.
Hardy-Weinberg acts as a null hypothesis for evolution because Hardy-Weinberg can ONLY
happen if no mechanisms of evolution are occuring (mutation, sexual selection, genetic drift,
gene flow, natural selection DO NOT occur in Hardy-Weinberg but are occuring in evolution)
Natural Selection: members of a species compete for resources and individuals with better
adaptations have a better chance at reproduction.
● It does not move toward perfection but moves toward what survives best in the circumstances; in some situations an adaptation is useful but in other environments it is
● Natural selection is non-random because the worst adapted produce the fewest offspring.
The genetic variation is random but the genetic variants that are useful will increase in
● Natural selection can only act on genes that cause a real life effect. If a unhelpful
recessive allele is hidden by a helpful Dominant one the unhelpful allele will not be
Types of Natural Selection
Stabilizing Selection / purifying Average is advantageous.
The bell curve gets tall and narrow
Directional Selection One extreme is advantageous.
The bell curve moves left/right
Disruptive Selection Average is disadvantageous / both extremes
The bell curve splits into two
● There are limits to adaptation because natural selection can only work on existing alleles.
● Also the ways in which the genes and traits are organised in the genome can cause
limitations. For example when increasing the beak strength of a finch the beak width is
also widened. It isnt possible to adapt to have both a narrow and strong beak.
Adaptation is not universally good because an adaptation in one environment or situation may be
harmful in another situation.
● Fitness tradeoff example: Peacock males are coloured to attract females and also attract
Mechanisms of Evolution
Mutation ● adds more variation
● they appear randomly and are passed down vertically
● can be helpful or disappear because it stops
Natural selection ● leads to adaptation
● reduces variation
Genetic Drift ● random fluctuation in allele frequency
● more effect on small populations than large ones
● in conservation biology: a near extinction species has a
small population, that population is more susceptible to a
reduction in variation making it harder to recover
● can lead to allele fixation / disappearance
● reduces variation
Gene flow ● migration
● makes populations more similar
● does not increase variation
Nonrandom mating ● sexual selection (type of natural selection) ● reduces variation
● Founder effect and population bottleneck are both drastic reduction in population size.
They make the population susceptible to genetic drift. Founder effect is when a small
peice of a