Genetics News Exam I Weekend help Summary for Exam II Lab 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 Monohybrid cross Quick review Chi2 test LOTS

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

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

Parental Cross Meiosis I Meiosis II

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

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.

Are Mendel’s conclusions valid? Mendel observed: Pp x Pp 705 purple + 224 white Mendel concluded: Pp x Pp 3:1 purple:white But 3:1 with 929 flowers is really: ~694 purple + 235 white 705 purple and 224 white is close... Is it close enough?

Where does 2 come from? A million repetitions of Mendel’s experiment Create a million universes -- purple:white on average = 3:1 Result: 702 purple 227 white = 929 plants Result: 695 purple 234 white = 929 plants Result: 710 purple 219 white = 929 plants Result: 698 purple 231 white = 929 plants Result: 688 purple 241 white = 929 plants Result: 705 purple 224 white = 929 plants

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

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

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?

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?

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 = 696.75 White = 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)

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%

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

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)

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

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?

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

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

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

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?