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Transcript
What do these images have in common?
What do these images have in common?
Microbacterium hatanonis is a new species of
extremophile bacteria so hardy that it lives and
reproduces in cans of hairspray.
A thread snake, Leptotyphlops carlae,
is the smallest known snake. Here, it is
coiled on an American quarter
Tahina spectabilis, a rare species of palm,
was discovered in Madagascar. It grows very tall,
blooms spectacularly once, produces fruit, then dies.
These photographs represent new species discovered and named since the year 2005.
App - Recent Adaptations in Humans HHMI's all slides
Microevolution
is when allele frequencies change from
generation to generation
-
is evolution on the smallest scale
App - Sickle Cell Anemia
microevolution
An example of
in humans is the prevalence of sickle-cell disease in Africa.
Sickle-cell disease causes weakness, pain, and even death.
The disease is caused by a
allele; if a person has two of these recessive alleles, they
disease.
Carriers (Heterozygotes) of the sickle-cell allele
have the disease, but are resistant to malaria.
recessive
have
do not
sickle-cell
changes to the gene pool
Evolution =
Without mutations and/or sexual reproduction, evolution does not occur.
No changes to the gene pool is called the
.
The Hardy-Weinberg Equilibrium occurs when the frequency of alleles in a gene pool is constant over time.
This equilibrium requires random mating, a large population, no movement in or out of the population, no mutations, and no
Hardy-Weinberg Equilibrium
natural selection.
In real life,
.
there are always some changes to disrupt this
Microevolution is the
disruption
of the
Hardy-Weinberg Equilibrium.
By applying genetics and mathematics to the theory of natural selection we can determine whether a population is evolving!!!!!!
Hardy-Weinberg Equilibrium
Frequencies of alleles are constant
Let p represent dominant allele
Let q represent recessive allele
Therefore
p+q =1
formula to calculate frequency of alleles
In order to determine if a population is evolving or not we need a baseline,
the formula to calculate frequency of genotypes (2 alleles) in a population
p2 + 2pq + q2 = 1
p2 + 2pq + q2 = 1
p2 - homozygous dominant
2pq - heterozygous
q2 - homozygous recessive
HWE Example
Approximately 16% of the population of mice have brown fur. The rest of the population has black fur. If we assume that the
brown fur are homozygous recessive for the gene b, what is the frequency of homozygous dominants (BB) in the population?
Of heterozygotes (Bb)?
Let B - black fur dominant
Let b - brown fur recessive
We need to determine whether the question is talking about one allele or about a genotype which consists of 2 alleles.
Brown fur - in order to show brown your genotype has to be bb, therefore the question is genotype
bb = 0.16 = q2
frequency of the homozygous recessive
square root of q = 0.4
p+q=1
p=1-q
= 0.6
BB = p2
= 0.36
= 36%
2 pq = 2 (0.6) (0.4) = 0.48
= 48%
frequency of the homozygous dominant
frequency of the heterozygotes
We now have a baseline to determine if evolution occurs over a period of time!
BB - 36%
Bb - 48%
bb - 16%
Microevolution is driven by natural selection, sexual selection, artificial selection, genetic drift, and gene flow.
Natural selection is not random.
The
individuals have a reproductive advantage, so the frequency of their alleles in the gene pool is higher.
S
in the environment change the relative frequencies of phenotypes in a population.
1) NATURAL SELECTION
fittest
elective pressures
App - Natural and Artificial Selection Slide 5 with videos
Stabilizing selection: the
Directional selection:
Disruptive selection:
phenotypes are favoured
most frequent
of the phenotypes is favoured
of phenotypes are favoured
one extreme
two or more extremes
Changes in the fitness of individuals changes the normal distribution of
phenotypes in the population.
- Masses of human babies at birth is an example of stabilizing sel.
- Pesticide and antibiotic resistance are examples of directional
selection.
- Darwin's finches is an example of disruptive selection
2) Sexual Selection
- Sexual selection is not random; mates are often chosen based on
their phenotype.
- Other individuals in the species screen, or select, the traits. The most
common forms are
and
competition
female mate choice
- In natural selection, the environment screens the traits.
male vs. male
3) Artificial Selection Examples
- Artificial selection is not random.
- Breeding programs are used to
produce desirable traits. (cats)
This registered American shorthair cat is the
- Artificial selection can have
result of artificial selection.
usually in the form of genetic diseases.
Eg. Horses HYPP (Hyperkalemic periodic paralysis is an inherited disease of the muscle which is
caused by a genetic defect)
Reducing genetic diversity making
species vulnerable
to
unintended
consequences
evolutionary forces
Activity C6 - Natural vs. Artificial
4) Genetic Drift
Is
, changing the gene pool due to chance
random
Each new generation has a shift in the frequency of alleles
based on which alleles get passed along to offspring
(for example, the recessive gene may be lost in a few generations)
Has a much greater effect on small populations
Can have a major effect on a population
- the
occurs when a population suddenly
decreases, often due to a natural disaster
- this decrease
variation in alleles in the population,
bottleneck
effectgenetic diversity
decreasing
- the
occurs in a new, isolated population
reduces
- this is likely what occurred
with Galapagos finches
founder effect
5) Gene Flow
Gene flow is a
process.
random
Populations of a species are often
by physical barriers,
isolated
like mountains or oceans.
- In gene flow, genes are exchanged between two different
populations if these barriers are overcome.
Interbreeding between populations
or changes
the frequency of alleles already present.
adds new alleles
Gene flow tends to
genetic differences between
populations.
If extensive enough, a single population
reducemight replace the smaller
ones that originally interbred.
Homework
3C
pg. 209 # 3~7, 12, 14, 15
pg. 223 # 7, 8, 9, 10, 12, 13
3U
pg. 209 # 3~7, 12, 14, 15
pg. 223 # 6~13