Announcements. 1. Answers to Ch. 3 problems 6, 7, 8, 12, 17, 22, 32, 35 posted - 230A. 2. Problem set 1 answers due in lab this week at the beginning of lab. Bring calculators to lab this week.
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1. Answers to Ch. 3 problems 6, 7, 8, 12, 17, 22, 32, 35 posted - 230A.
2. Problem set 1 answers due in lab this week at the beginning of lab. Bring calculators to lab this week.
3. Getting to know Flylab and testcross (lab 2) - printout of assignments from “notebook”, due this week at the beginning of lab.
4. Confusion with X-linked crosses: 1 cross or 2?
5. Seminar this Thursday - faculty research interests
1. Genetic ratios are expressed as probabilities. Thus, deriving outcomes of genetic crosses relies on an understanding of laws of probability, in particular: the sum law, product law, conditional probability (likelihood that one outcome will occur, given a particular condition), and the binomial theorum (used to determine particular combinations). Expand the binomial OR use factorial general formula to solve.
2. Statistical analyses (Chi square) - used to test the validity of experimental outcomes. In genetics, some variation is expected, due to chance deviation.
I. Chi-square revisited
- solving pedigree problems
where o = observed value for a given category,
e = expected value for a given category, and sigma is the sum of the calculated values for each category of the ratio
A 750 760
Null Hypothesis: Data fit a 3:1 ratio.
degrees of freedom = (number of categories - 1) = 2 - 1 = 1
Use Fig. 3.12 to determine p - on next slide
Do not reject
0.50 > p > 0.20
Conversely, 52% of the repeats would show less deviation as a result of chance than initially observed.
I say that I have a non-trick coin (with both heads and tails).
Do you believe me?
1 tail out of 1 toss
10 tails out of 10 tosses
100 tails out of 100 tosses
Compare Chi-square with 3.84 (since there is 1 degree of freedom).
a) Tails 1 of 1
b) Tails 10 of 10
c) Tails 100 of 100
F2 data: 792 long-winged (wildtype) flies, 208 dumpy-winged flies.
Hypothesis: dumpy wing is inherited as a Mendelian recessive trait.
What do the data suggest about the dumpy mutation?
The complex study of human genetics - we don’t control human matings! Instead, we study family trees (pedigrees) to identify how traits are inherited.
D is a dominant allele interfering with bone growth.
Most people are dd.
Parents and 1 boy, 1 girl (in order of birth)
Heterozygotes for autosomal recessive
Number of children of sex indicated
How is this trait inherited? dominant or recessive?
What are most probable genotypes of each individual?
Unaffected 2nd generation = rare, recessive trait
Folksinger Woody Guthrie died of Huntington’s Disease.
HD = Huntington’s allele, hd = wildtype allele; data suggests Huntington’s Disease is autosomal dominant.