1. Genetics News Exam I Weekend help Summary for Exam II Lab
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Weekend help
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Summary for Exam II
Lab
Figure out dilutions

2. Topics for Today Terminology Not today Monohybrid cross Quick review
Chi2 test
LOTS

3. Monohybrid Cross P ...GGACCGAT… ...GGATCGAT…
…CCTGGCTA...
...GGATCGAT…
…CCTAGCTA...
Colorless compound Purple compound
Enzyme P

4. Study Question 7 Which is the dominant allele?
Heterozygous Pp
Homozygous PP
Homozygous pp
If Pp has P phenotype,...
then P is dominant over p

5. Parental Cross
Meiosis I
Meiosis II

6. Study Question 8
Parental Cross
Write down the genotypes of the two F1 parents and the gametes they produce

7. Restate the Law of Segregation in the language of chromosomes
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.

8. Are Mendel’s conclusions valid?
Mendel observed:
Pp x Pp purple white
Mendel concluded:
Pp x Pp :1 purple:white
But 3:1 with 929 flowers is really:
~694 purple white
705 purple and 224 white is close...
Is it close enough?

9. Where does 2 come from? A million repetitions of Mendel’s experiment
Create a million universes -- purple:white on average = 3:1
Result: purple white = 929 plants
Result: purple white = 929 plants
Result: purple white = 929 plants
Result: purple white = 929 plants
Result: purple white = 929 plants
Result: purple white = 929 plants

10. Where does 2 come from? A million repetitions of Mendel’s experiment

11. Where does 2 come from? A million repetitions of Mendel’s experiment

12. Where does 2 come from? A million repetitions of Mendel’s experiment
Study Question 14: Why is it that the two dotted lines are on opposite sides of the mean?
Study Question 15: What’s the most likely result? How often does it occur?

13. Deviation from Expectation Two 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?

14. Steps in Performing a Chi2 Test
Determine the expected values for the experiment
Model: 3 purple : 1 white flower Total counted: 929 Purple = 75% of 929 = White = 25% of 929 =
Calculate the squares of the deviations
Chi2 = Sum of (O - E)2 / E
Chi2 = ( )2 / ( )2 / ~82 / ~82 / ~ ~ Chi2 = approx (actually = 0.37)

15. Steps in Performing a Chi2 Test
Determine the degrees of freedom
What was the experiment? Count 929 flowers a million times Ask: purple? (if not, then white)
Therefore ONE degree of freedom
Look up probability for 2 value
2 = 0.30
80% > P > 50%. Call it ~60%

16. Steps in Performing a Chi2 Test
Draw a conclusion
60% of the time, Mendel’s result or worse would have arisen by chance if purple:white truly occurs in a 3:1ratio.
The hypothesis has a 50% chance of being correct
The result has a 50% chance of being correct

17. Deviation from Expectation Two 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)

18. Study Question 25
Are there as many female as male biology majors? How many degrees of freedom?
What’s the experiment?

19. 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?

20. 1000’s of marbles! 50% red, 50% blue Guaranteed!
Bag of Marbles
1000’s of marbles! 50% red, 50% blue Guaranteed!

21. How to tell how close is close enough?
Test Claim of 50%:50%
47 marbles
53 marbles
100 marbles
Is their claim correct?
How to tell how close is close enough?
TOTAL

22. 2 Test of Claim Chi2 = Sum of (O - E)2 / E
P = ~60%
P = ?

23. 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 3:1 ratio?