BICD 100 Lecture Notes  Lecture 2: ChiSquared Distribution, Mendelian Inheritance, Punnett SquarePremium
2 pages109 viewsWinter 2019
Department
Biol/Genetics,Cellular & DevelopCourse Code
BICD 100Professor
Deborah YelonLecture
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Following two traits at once.

Crossed yellow and round peas with green and wrinkled peas

F1 is all round and yellow peas

Now we can get new combinations like yellow and wrinkled and green and round
○
F2 selffertilized generation gets 9/16 y/r, 2/16 y/w, 3/16 g/r, and 1/16 g/w.

Each postulate has its exceptions so is not necessarily always true
□
During gamete function, segregating pairs of unit factors (genes) assort independently
of each other
▪
Independent assortment
○
Mendel's 4th postulate

O
GW
Gw
gW
gw
GW
GGWW
GGWw
GgWW
GgWw
Gw
GGWw
GGww
GgWW
Ggww
gW
GgWW
GgWw
ggWW
ggWw
gw
GgWw
Ggww
ggWw
Ggww
○
Now we can see the 9:3:3:1 ratio present with a heterozygous dihybrid cross
Draw a Punnett square of a GgWw xGgWw dihybrid cross

The above ratio is phenotypic but the genotypic ratio is more complicated

When two independent events occur simultaneously, the combined probability of the 2
outcomes is equal to the product of their individual probabilities. p(A and B) = p(A)*p(B)
○
Product law of probabilities

Dihybrid cross:
Taking reallife data and deciding if it fits your genetic hypothesis

Chisquare analysis evaluates the influence of chance on data

Are they significantly different
○
X^2= sigma(OE)^2/E
○
Statistical test to check your experimental results against expected ratios

Null hypothesis: any differences between expected values and observed values are likely to be due
to chance

Alternate hypothesis: the differences between expected and observed values are significant and
unlikely

Chisquare analysis
State the null hypothesis

Calculate expected numbers of progeny

Use formula to calculate chisquare value

Use table to translate chisquare into p value

Draw conclusion about hypothesis

Five steps of chi
Low p value means that the difference between your observe3d results and the expected
results is unlikely to be due to chance
○
P value less than 0.05 means you can reject the null hypothesis
Probability that your results are due to chance

Meaning of a p value
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