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Microevolution and
Microevolution is evolution that occurs within a
population or a change in the gene pool over
a succession of generations
Macroevolution is evolutionary change on a grand
scale, encompassing the origin of novel
designs , evolutionary trends, adaptive
radiation, and mass extinction
O. Experiencing the Hardy-Weinberg
Equilibrium formula.
J. How do we know that a population is
novel designs like feathers & wings,
upright posture in humans
trends like increasing brain size in
adaptive radiation is seen in flowering
*mass extinction like the dinosaurs
Hardy-Weinberg Theorem
Before we can look at microevolution
we must consider the H-W theorem
A few definitions first:
Population- all the members of a single species
occupying a particular area at the same
species- organisms that share a common gene
pool, interbreed with one another
gene pool- total of all the genes of all the
individuals in a population
P 394 for gene frequenciies in iText
Hardy-Weinberg Theorem
Describes a nonevolving population. It states
that the frequencies of alleles and genotypes
in a population’s gene pool remain constant
over the generations unless acted upon by
agents other than sexual recombination. So
sexual shuffling of alleles due to meiosis and
random fertilization have no effect on the
overall genetic structure of a population.
5 conditions that must be
met to maintain equilibrium
population must be very large
population must be isolated from
no mutations
random mating must occur
no natural selection can occur
Causes of microevolution
• genetic drift
• gene flow
• mutations
• nonrandom mating
• natural selection
If any of these occur then equilibrium is
NOT present in the population!
Genetic drift- changes in a gene
pool of a small population due to
2 situations that can lead to genetic drift:
1. bottleneck effect- disasters such as
earthquakes or floods reduce the
population drastically, killing victims
unselectively, reduces variability
2. founder effect-a small number of
individuals colonize an isolated island,
lake, or some other new habitat
Gene Flow
-population may gain or
lose alleles by gene flow, genetic
exchange due to the migration of
fertile individuals or gametes
between populations
ex. – humans moving around the world
-a change in an organism’s DNA
Nonrandom mating or
assortive mating
individuals selecting mates because of a
particular phenotype
ex. cardinals with the brightest red
Natural Selection
differential success in reproduction because an
organism is more fit for their environment
O. Getting the Hardy-Weinberg Equilibrium
Write this down in your journal.
Test on Evolution (14,15,16) on Wed.(if on
field trip) or Thursday if going to be
Study Guide answers online
Quiz answers online
Study this weekend!
wildflower population
two colors of flowers A – pink, a – white
500 plants = 1000 genes
20 white plants = 40 a alleles
the other 480 are pink =
320 are AA=640 A alleles
160 are Aa =160 A alleles, 160 a alleles
So the frequency of gene A is 800/1000 = .8=80%
the frequency of gene a is 200/1000 = .2 =20%
p = frequency of gene A
q = frequency of gene a
If you consider genotypic frequencies
AA = 320/500=.64=64%
Aa = 160/500= .32=32%
aa = 20/500=.04=4%
Hardy-Weinberg equation:
(frequency of (frequency of
AA genotype) Aa genotype)
For wildflowers
= 1
(frequency of
aa genotype)
.64 + .32 + .04 = 1
Maple syrup urine disease (MSUD) is
autosomal recessive and causes intellectual
and physical disability, difficulty feeding, and a
sweet odor to urine. In Costa Rica, 1 in 8000
newborns inherits the condition. What is the
carrier frequency of MSUD in this population?