2/2 Daily Catalyst Pg. 76 Chi-Squared
 1. Write the equation for chi-squared and define each of the
terms.
 2. What p-value do we use in AP Biology?
 3. In a dihybrid cross, what fractions do we expect if the
parents are both heterozygous?
2/2 Class Business Pg. 76 Chi-Squared
 Unit #7 test Genetics
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Wednesday, Feb. 3rd
Study guide due test day
Blood types lab tomorrow
Tutoring available!
 Unit #8 Energy
 Mini-test Thursday, Feb.12th
 Review packet over Mardi Gras
2/2 Agenda Pg. 76 Chi-Squared
 Daily Catalyst
 Class Business
 Review pedigrees
 Chi-squared problems
 Practice
Chi-Squared
 You are looking at two traits, kernel color and texture. To obtain
the variety we see below, the parents (p gen) must have been
heterozygous for both traits. Purple and smooth are dominant
traits and yellow and wrinkled are recessive traits.
 Due to the phenotypic ratio we know, what do we expect?
 9/16 Purple and smooth
 3/16 Purple and wrinkled
 3/16 Yellow and smooth
 1/16 Yellow and wrinkled
Chi-Squared
 When you count the kernels on the corn cob, you see the
following data:
Kernels
# Counted
 Is this that we expect?
Purple and
smooth
12
Purple and
wrinkled
9
Yellow and
smooth
7
Yellow and
wrinkled
6
Total
34
Chi-Squared
kernels
Ratio
Decimal
Work
Expected
Observe
Purple and 9/16
smooth
.56
.56 X 34
19
12
Purple and 3/16
wrinkled
.19
.19 X 34
6.4
9
Yellow
and
smooth
3/16
.19
.19 X 34
6.4
7
Yellow
and
wrinkled
1/16
.06
.06 X 34
2.2
6
=34
=34
=1.00
Answer
 10.26
Problem #1
 1. Problem: A large ear of corn has a total of 433 grains, including
271 Purple & starchy, 73 Purple & sweet, 63 Yellow & starchy, and
26 Yellow & sweet.
 Your Tentative Hypothesis: This ear of corn was produced by a
dihybrid cross (PpSs x PpSs) involving two pairs of heterozygous
genes resulting in a theoretical (expected) ratio of 9:3:3:1.
 Objective: Test your hypothesis using chi
square and probability values.
 Expected
 Purple and Smooth 9/16 of 433 = 243.6
Purple and Wrinkled 3/16 of 433 = 81.2
Yellow and Smooth 3/16 of 433 = 81.2
Yellow and Wrinkled 1/16 of 433 = 27.1
Problem #2
 2. Problem: In a certain reptile, eyes can be either black or yellow. Two black
eyed lizards are crossed, and the result is 72 black eyed lizards, and 28 yelloweyed lizards.
 Your Tentative Hypothesis: The black eyed parents were Bb x Bb.
 Objective: Test your hypothesis using chi square analysis.
 Expected
 If you do a punnet square of Bb x Bb, you get an expected percentage of 25%
and 75% or 1/4 and 3/4
 Since the total number of lizards is 100, the observed is already in the correct
ration
 Expected ....................... Observed
 Black Eyes = 75 ................ 72
Yellow Eyes = 25 ............. 28
 .12 + .36 = .48
 Good FIT
Problem #3
 3. Problem: A sample of mice (all from the same parents) shows
 58 Black hair, black eyes 16 Black hair, red eyes
19 White hair, black eyes 7 White hair, red eyes
 Your tentative hypothesis: (what are the parents?)
 Looks like a 9/3/3/1 ratio, meaning the parents are HhEe x HhEe
 Total number of offspring = 100
 Expected
 9/16 of 100 = 56.25
3/16 of 100 = 18.75
3/16 of 100 = 18.76
1/16 of 100 = 6.25
 .05 + .40 + .003 + .09 = .54 = GOOD FIT
2/2 HW
 1. In a certain species of flowering plant, the red allele R is
dominant to the white allele, r. A student carried out a cross
between a red flowered plant and a white flowered plant. When
planted, the 158 seeds that were produced from the cross matured
into 92 plants with red flowers and 66 plants with white flowers.
Calculate the chi squared value for the null hypothesis that the red
flowered parent was a hybrid for the flower color gene. Give your
answer to the nearest tenth.
2/2 HW
 1. A genetics engineer was attempting to cross a tiger and a
cheetah. She predicted a phenotypic outcome of the traits she was
observing to be in the following ratio: 4 stripes only, 3 spots only, 9
both stripes and spots. When the cross was performed and she
counted the individuals she found 50 with stripes only, 41 with
spots only and 85 with both. According to the Chi-square test, did
she get the predicted outcome?
2/2 HW
 Define nondisjunction
 Provide an example
 What is the impact of nondisjunction?