Download Exam 1 Answers

Exam 1 Answers
Name:________________________
Biology 210
Sept. 20, 2006
Section:______________________
1. (5 points) Circle the answer that gives the maximum number of different alleles that might
exist for any one locus in a normal mammalian cell.
A. 1
D. 4
B. 2
E. 8
C. 3
F. Many
2. (6 pts) Suppose you want to determine the genotype of a mouse (“Pinky”) who has the
dominant phenotype at some locus. (as opposed to having the recessive phenotype at this
locus)
A. What do you call the kind of cross you must do? (one phrase)
A testcross
B. What must be true (genotypically) of the mouse that you mate with Pinky?
That mouse must be homozygous recessive.
C. What are the phenotypes and ratios that you would expect in offspring from this
mating if Pinky is heterozygous?
½ the mice will have the dominant phenotype and ½ the mice will have the
recessive phenotype.
3. (9 pts) Consider three gene pairs Aa, Bb, and Cc, each of which assorts independently and
affects a different trait. The upper case represents a dominant allele and the lower case
represents a recessive allele. Give the probability for obtaining each of the following:
A. an AaBb genotype from a cross between parents who are
AaBb x Aabb
½
x ½ = 1/4
B. an AabbCC genotype from a cross between parents who are
AaBbCc x AABbCC
½ x ¼ x ½ = 1/16
C. an a, b, c phenotype from a cross between parents who are
AaBbCC x AabbCC
Probability of c phenotype is 0, so answer is 0
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4. (6 pts) The cells in the following figure were all taken from the same Andean rose rat.
Identify the cell division (mitosis, meiosis I, or meiosis II) AND the phase for each cell
(prophase, metaphase, etc.).
____anaphase of meiosis II___________________________
__metaphase of mitosis_________
________prophase of meiosis I________________
5. (8 pts) What is the sex of an XXY individual in humans?_____Male_________
What is the sex of an XXY individual in Drosophila (fruit
flies)?____Female___________
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6. (10 pts) The students in a Biology 210 genetics class did a cross by breeding tall cougar daisies
with short cougar daisies and analyzed the progeny. They believed that they were looking at one
trait in which the short daisies were homozygous recessive and the tall daises had at least one
dominant allele. 60 of the progeny were tall and 40 were short. They did a chi square analysis to
Answer if 3:1 expected if 1:1 expected
determine if these results supported their hypothesis.
A. What were the total number of progeny observed? _______100_
___100___
B. How many degrees of freedom are there in their analysis?___1______
1
C. What is the value for Chi-squared (X2)? _________________12
4___
NOTE: There was a problem with the way I worded this question versus the way I described it
when there were questions during the exam, so we are giving credit for this question, whether you
did it as if it is a test-cross (as worded here), or as one of Mendel’s monohybrid crosses: (TT x tt
= P1, giving rise to F1s that are all Tt, which, when crossed would be predicted to give a 3:1
phenotypic ratio). The only requirement was that you were consistent throughout your analysis,
ie, you did an analysis with expected ratios of either 1:1 or of 3:1.
If expect 3:1 (Tt x Tt), P is P < 0.005
If expect 1:1 (T_ x tt), P is between 0.05 & 0.01
D. Circle the correct value for P:
P > 0.05
P is between 0.05 & 0.01
P is between 0.01 & 0.005
P < 0.005
E. Are the results consistent with their hypothesis (yes or no)? _No, by either scenario__
7. (8 pts) What do we mean when we say that epistasis is occurring? Do not use examples in
answering this question. (one sentence only)
One gene is masking the expression of another gene. (must be clear that you are referring to at
least 2 different loci.)
3
8. (12 pts) The pedigree below is for a rare autosomal recessive genetic disease (d) in which
all the individuals with the disease are shaded. The genotype is given for some of the
individuals who do not have the disease.
A. Next to each of the 4 individuals with an arrow pointing to them write all of the
possible genotypes they could have.
B. Inside of the circle or square for each of those 4 individuals, give the probability
that they are a carrier.
C.?? If Bob and Julie are thinking about having another child. What is the probability
that their child will have the disease?
1/4
DD
DD
DD or Dd
1/2
1
Dd
Dd
Dd
1
DD
1
2/3
Dd or DD
9. (5 pts) In order to determine if two independently isolated mutations from different
individuals are at the same locus or at different loci, which test would you perform?
A. a test cross
B. an epistasis test
C. a complementation test
D. a dihybrid test
E. a biochemical test
10. (4 pts) All the ABO blood type alleles map to a single gene locus. True or False?
4
11. (12 pts) A father has hemophilia B, an X-linked recessive disease. He and his wife, who
carries no allele for the disease, have a boy and a girl.
A. What is the probability that the girl will carry an allele for the disease?__1.0_____
B. What is the probability that the boy will have the disease?_______0________
C. If their girl eventually marries a normal man (sometimes they’re hard to find!) and
they have a son, what is the probability that this son will have hemophilia
B?_____1/2______
12. (5 pts) A child has type AB blood, and her mother has type A blood. Give all
possible genotypes and blood types for the father of this child.
(Child must be iAiB. The Mother contributed the iA allele, so...) The father, who
contributed an iB allele, can have either type AB blood (genotype iAiB), or type B
blood ( genotype iOiB or iBiB).
13. (10 pts) In the following cross between AaBb heterozygotes (AaBb x AaBb), the
biochemical pathway given below also shows the colors of the compounds produced.
What is the phenotype you would obtain for each of the genotypes listed below, AND
what are the phenotypic ratios you will derive from this cross. Assume that the
phenotype is ‘white’ unless otherwise indicated.
ABlue
Green
BBlue
Genotype: A-BPhenotype: __green____
A-bb
_blue___
aaB___blue___
aabb
__white___
Phenotypic ratios (include the phenotype with each number):
_________9 green: 6 blue: 1 white________________________
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