g e n e t i c s n e w s
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G e n e t i c s N e w s. Exam I Returned Monday (?) Our responses on web Thanks for YOUR responses Weekend help Sun 4:30 (S-111) Sun 8:00 (E-107) Summary for Exam II Lab Figure out dilutions. Topics for Today. Terminology. Not today. Quick review. Monohybrid cross. LOTS. - PowerPoint PPT PresentationTRANSCRIPT
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Genetics News• Exam I
– Returned Monday (?)
– Our responses on web– Thanks for YOUR responses
• Weekend help– Sun 4:30 (S-111)– Sun 8:00 (E-107)
• Summary for Exam II
• Lab– Figure out dilutions
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Topics for Today
Terminology Not today
Monohybrid cross Quick review
Chi2 test LOTS
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Monohybrid Cross
Colorless compound Purple compoundEnzyme
P
...GGATCGAT… …CCTAGCTA...
...GGACCGAT… …CCTGGCTA...
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Study Question 7Which is the dominant allele?
Homozygous PP Homozygous pp
Heterozygous Pp
then P is dominant over pIf Pp has P phenotype,...
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Parental Cross
Meiosis I
Meiosis II
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Study Question 8
Write down the genotypes of the two F1 parents and the gametes they produce
Parental Cross
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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 allelesLaw of Segregation: Each of two homologous chromosomes has an equal chance of arising in a gamete through meiosis.
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Are Mendel’s conclusions valid?
Mendel concluded:
Pp x Pp 3:1 purple:white
Mendel observed:
Pp x Pp 705 purple + 224 white
But 3:1 with 929 flowers is really:
~694 purple + 235 white
705 purple and 224 white is close...
Is it close enough?
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Result: 705 purple 224 white = 929 plantsResult: 698 purple 231 white = 929 plantsResult: 688 purple 241 white = 929 plantsResult: 710 purple 219 white = 929 plantsResult: 695 purple 234 white = 929 plantsResult: 702 purple 227 white = 929 plants
Where does 2 come from?A million repetitions of Mendel’s experiment
Create a million universes -- purple:white on average = 3:1
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200,000 repetitions
Where does 2 come from?A million repetitions of Mendel’s experiment
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500,000 repetitions
Where does 2 come from?A million repetitions of Mendel’s experiment
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Where does 2 come from?A million repetitions of Mendel’s experiment
1,000,000 repetitionsStudy Question 15: What’s 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 18:The 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 / EChi2 = (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)
Look up probability for 2 value
2 = 0.30
80% > P > 50%. Call it ~60%
Therefore ONE degree of freedom
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Steps in Performing a Chi2 Test
P ~60%
Draw a conclusion
The result has a 50% chance of being correctThe hypothesis has a 50% chance of being correct60% of the time, Mendel’s result or worse would have arisen by chance if purple:white truly occurs in a 3:1ratio.
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Deviation from ExpectationTwo example experiments
Study Question 20:What if Mendel had counted not 929 but 929,000 plants -- what does the curve and shading look like then? (d still = 29)
P = .50 P = ???
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Study Question 25
Are there as many female as male biology majors? How many degrees of freedom?
What’s 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
1000’s of marbles!50% red, 50% blue
Guaranteed!
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Test Claim of 50%:50%
47 marbles
53 marbles
100 marblesTOTAL
Is their claim correct?
How to tell how close is close enough?
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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
Does dwarfism appear to be dominant or recessive?
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.
Can progeny be reasonably be described as in 3:1 ratio?