Download Day 5: Causes of Microevolution

Day 5: Causes of Microevolution
1. Genetic Drift- loss of variation (allele frequencies) due to
a sudden environmental act that reduces the population
2. Gene Flow – change in variation (allele frequencies) due
to immigration or emigration, movement of individuals
into or out of the population
3. Mutation- introduction of a new allele that becomes
established in the gene pool
4. Natural Selection- differential reproductive success, due
to environmental pressure on a favorable phenotype
5. Non-Random mating -mate choice is no longer based on
equal chance or opportunity. Mate choice has become
selective and based on some characteristic
Day 5: HW equilibrium
Evolution occurs at the population level, population is
defined as a group of the same species that live in the same
area and interbreed, producing fertile offspring.
• Hardy Weinberg equilibrium theory states that a population’s
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allele frequencies will remain unchanged generation after
generation, no evolution, if the following 5 conditions are
held constant:
Mutations do not change gene pool
Mating is random and each organism has equal opportunity
No natural selection, no phenotype is more favorable
Population is large and contains variation
No gene flow (emigration, immigration in/out of population)
Day 5: The equation
used to determine if a population’s allele frequency is changing,
in other words is the population “evolving”?
p2 + 2pq + q2 = 1
p = dominant allele
q = recessive allele
Each letter represents the frequency
of a particular allele in the
population
p+q=1
p2= Homozygous dominant genotype
(AA)
2pq= Heterozygous genotype (Aa)
q2= Homozygous recessive genotype (aa)
Day 5: using the equation
We can look at a population and identify specific
traits or phenotypes.
We can actually count the number of individuals
with those specific traits.
Ex. If there are 100 pigs 25 of them are black and 75
of them are pink, or 25% is black and 75% is pink.
What if you knew the black allele was Dominant
and the pink allele was Recessive. Could you
determine which ones had which genotype?
Day 5: HW equilibrium problem
• If B= Black skin and b= pink skin in a pig
• If 25% of the population were black and 75% were pink,
how many of them are
– Homzygous recessive bb
– Homzygous dominant BB
– Heterzygous Bb
• Remember that p is the dominant allele and q is the recessive
allele.
• What does bb, BB, and Bb look like?
• BB- black Bb- black
bb- pink
• p2- black 2pq- black q2= pink
• Can we calculate q? yes if we know q then we can find p
Day 5: practice problems
q= 0.6
1. A randomly mating
population has an
established frequency of
36% for organisms
homozygous recessive for a
given trait. What is the
frequency of the recessive
allele in the gene pool ?
a.
b.
a.0.6, b. 0.4,
c. AA=.16 and Aa= .48
2. You have sampled a
population in which you
know that the percentage of
homozygous recessive
genotypes (aa) is 36%.
Calculate the following
a. The frequency of the a
allele
b. The frequency of the A
allele
c. Frequency of AA and Aa