Download Process of Evolution

Process of Evolution
Wednesday, February 18th
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What do you think the term microevolution means?
What do you believe some of the causes for
microevolution are?
Monday, February 23rd
•
In a population, if no mutations occurred in the
individuals what do you think would happen in the
gene pool of the succeeding generations?
Tuesday, February
•
th
24
If a population if 36% of the individuals are
homozygous dominant, what % of the population
has the recessive phenotype, assuming HardyWeinberg equilibrium?
Wednesday, February
•
th
25
Of the 5 conditions of H-W equilibrium, which could
cause the greatest change in a population if it were
applied? Why?
See your notes if you don’t remember the 5
conditions!
Thursday, February
•
th
26
In natural selection, there are three types of
selection that occur, one of those being directional
selection. What do you think is occurring in a
population with this type of selection.
Friday, February
•
th
27
Would you like the idea of preparing for the AP test
outside of class? What days and times would you be
willing to attend?
Evolution in a Genetic
Context
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Darwin knew that members of a population varied
but he did not know how variations came about and
they were transmitted in populations
•
Around the 1930s, geneticists were able to apply
concepts of genetics to Darwin’s idea of populations
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We now recognize this as a way that evolution has
occurred
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Population: all members of a single species
occupying a particular area at the same time
•
Microevolution: Evolution that occurs within a
population
•
Population Genetics: study of gene frequencies in
and their changes within a population
•
Gene Pool: total of all genes of all the individuals in
a population
Allele Frequencies
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It is customary to describe the gene pool of a
population in terms of gene frequencies
•
To calculate the frequency of each allele, you must
have the # of each genotype (homo dominant,
heterozygous, homo recessive) & the total # of
individuals of a population
ozygous dominant for red eyes, 1/2 are heterozygous and 1/4 hom
at is the number of the allele R and the allele r in the populati
Hardy-Weinberg Law
•
Because of the result of calculating the frequency of alleles, we can
determine that sexual reproduction ALONE cannot bring about change in a
gene pool
•
G.H. Hardy (English Mathematician) & W. Weinberg (German Physician)
recognized the potential constancy, or equilibrium state, of gene pool
frequencies
•
Used a binomial expression to calculate the genotypic and allele
frequencies of a population
•
Hardy-Weinberg Equation:
p2 + 2pq + q2
•
p2 = % homozygous dominant individuals (AA)
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p = frequency of dominant alleles
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q2 = % homozygous recessive individuals
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q = frequency of recessive allele
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2 pq = % heterozygous individuals
p+q=1 (Sum of frequencies in both alleles is 100%)
p2+2pq+q2=1
•
H.W Law states that equilibrium of allele
frequencies in a gene pool, will remain in effect in
each succeeding generation of a sexually
reproducing population as long as 5 conditions are
met
•
5 conditions:
1. No Mutations: allelic changes do not occur, or changes in one
direction are balanced by the changes in the opposite direction
2. No Gene Flow: migration of alleles into or out of the population
does not occur
3. Random Mating: individuals pair by chance and NOT according
to their genotypes and phenotypes
4. No Genetic Drift: the population is very large , and changes in
allele frequencies due to chance alone are insignificant
5. No Selection: no selective agent favors one genotype over
another
Why is H-W Law Important?
•
Provides a baseline by which we can judge if
evolution has occurred
•
In life, the 5 conditions for maintaining equilibrium of
allele frequencies, are rarely met if ever; hence the
fact we have genetic variation
•
Any change of allele frequencies in the gene pool of
a population signifies evolution has occurred
Calculating Gene Pool Frequencies using H-W
•
16% of the human population has a continuous
hairline (recessive trait). Using this information
complete all the allele and genotypic frequencies for
the population. Assuming H-W equilibrium
conditions are met.
Where do we start?
SOLVE!
•
What percentage of the population will have the
dominant phenotype? Recessive?
H-W Lab: Case #2
•
Recall the five requirements of H-W equilibrium
1. For your row (Labels for each row are placed at the
front), describe how you will modify that H-W
requirement, so that it no longer applies to your
experiment
2. Next, draw out another data just as you did
yesterday; label this graph as “Out of Equilibrium”
3. Take your pre-sorted cup of alleles, decide which color
will be dominant and which will be recessive
4. Record the number you have of each allele
(ex. 25 - B, 35 - b)
5. Using the H-W equation, do the % of dominant alleles
and recessive alleles in the population (ex. 25/100 = 25%)
6. Apply the modification you came up with to your
population (ex. Having no random mating, you would
specifically pick out the genotypes you want)
7. Perform 5 generations, as you did yesterday, record your
data
8. Compare the results you got in your group to
another groups results. Similarities? Major
differences?
9. Answer the questions for each Case Study (#1 and
#2).
10. Turn in your data tables, graphs and answers to
your questions.
11. Once you finish with the lab, you can work on the
H-W Practice Problems I gave you for HW this week
and the Post-Learning portions for your journals! 