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Genetics News

• Exam I
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• Sun 430 (S-111)
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• Summary for Exam II
• Lab
• Figure out dilutions

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Topics for Today
Terminology
Not today
Quick review
Monohybrid cross
LOTS
Chi2 test
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Monohybrid Cross
...GGACCGAT CCTGGCTA...
...GGATCGAT CCTAGCTA...
Colorless compound Purple compound
Enzyme
P
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Study Question 7Which is the dominant allele?
Heterozygous Pp
Homozygous PP
Homozygous pp
If Pp has P phenotype,...
then P is dominant over p
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Parental Cross
Meiosis I
Meiosis II
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Study Question 8
Parental Cross
Write down the genotypes of the two F1 parents
and the gametes they produce
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F1 Cross
Meiosis I
Study Question 13 Restate the Law of Segregation
in the language of chromosomes
Law of Segregation Heterozygotes produce equal
numbers of the two alleles
Law of Segregation Each of two homologous
chromosomes has an equal chance of arising in a
gamete through meiosis.
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Are Mendels conclusions valid?
Mendel observed Pp x Pp 705
purple 224 white
Mendel concluded Pp x Pp
31 purplewhite
But 31 with 929 flowers is really 694 purple
235 white
705 purple and 224 white is close...
Is it close enough?
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Where does ?2 come from?A million repetitions of
Mendels experiment
Create a million universes -- purplewhite on
average 31
Result 705 purple 224 white
929 plants
Result 698 purple 231 white
929 plants
Result 688 purple 241 white
929 plants
Result 710 purple 219 white
929 plants
Result 695 purple 234 white
929 plants
Result 702 purple 227 white
929 plants
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Where does ?2 come from?A million repetitions of
Mendels experiment
200,000 repetitions
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Where does ?2 come from?A million repetitions of
Mendels experiment
500,000 repetitions
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Where does ?2 come from?A million repetitions of
Mendels experiment
1,000,000 repetitions
Study Question 15 Whats the most likely result?
How often does it occur?
Study Question 14 Why is it that the two dotted
lines are on opposite sides of the mean?
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Deviation from ExpectationTwo example experiments
Study Question 17 Why is there shading on both
sides of the curve?
Study Question 18The farther away O from E, the
smaller/larger the shaded area?
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Steps in Performing a Chi2 Test
Determine the expected values for the experiment
Model 3 purple 1 white flowerTotal counted
929Purple 75 of 929 696.75White 25 of
929 232.25
Calculate the squares of the deviations
Chi2 Sum of (O - E)2 / E
Chi2 (705 - 696.75)2 /696.75 (224 - 232.25)2
/232.25 82 / 700
82 / 230 0.09
0.3 Chi2
approx 0.39 (actually 0.37)
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Steps in Performing a Chi2 Test
Determine the degrees of freedom
What was the experiment? - Count 929 flowers
a million timesAsk purple? (if not, then white)
Therefore ONE degree of freedom
Look up probability for ?2 value
?2 0.30 80 gt P gt 50. Call it 60
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Steps in Performing a Chi2 Test
P 60
Draw a conclusion
The result has a 50 chance of being correct
The hypothesis has a 50 chance of being correct
60 of the time, Mendels result or worse would
have arisen by chance if purplewhite truly
occurs in a 31ratio.
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Deviation from ExpectationTwo example experiments
P .50
P ???
Study Question 20What if Mendel had counted not
929 but 929,000 plants -- what does the curve and
shading look like then? (d still 29)
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Study Question 25
Are there as many female as male biology majors?
How many degrees of freedom?
Whats the experiment?
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Study Questions 27 and 28
Does a high P value indicate the hypothesis is
correct?
Does a low P value indicate the hypothesis is
incorrect?
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Bag of Marbles
1000s of marbles!50 red, 50 blue Guaranteed!
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Test Claim of 5050
Is their claim correct?
47 marbles 53 marbles 100 marbles
How to tell how close is close enough?
TOTAL
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?2 Test of Claim
Chi2 Sum of (O - E)2 / E
Chi2 (53 - 50)2 /50 (47 - 50)2 /50
9 / 50 9 / 50
18/50
0.36
P ?
P 60
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Study Question 26
Although dwarfism is a rare condition in humans,
it is nonetheless not so uncommon to encounter a
productive union between two dwarves. Suppose you
consider the progeny of many such unions and find
that 132 are also dwarves and 60 are of normal
stature.
Does dwarfism appear to be dominant or recessive?
Can progeny be reasonably be described as in 31
ratio?