Name: _____________________________
Genetics 314 – Spring, 2007
Exam 4 – 100 points
Part 1 – 76 points: Answer all questions
1. What are Mendel’s two laws and how do they relate to events in meiosis?
2. You are studying six traits in fruit flies (Drosophila) and all the traits act
independently. You mate the following genotypes:
Aa Bb Cc Dd Ee Ff
x
Aa Bb Cc dd Ee FF
Out of 4000 progeny how many of the following genotypes would you expect to
recover?
1) AA BB CC DD EE FF
2) Aa Bb Cc Dd Ee Ff
3) Aa Bb cc Dd Ee FF
4) aa bb cc dd ee FF
1
Name: _____________________________
3. You are studying large families to determine if there is an environmental influence on
the sex of children in large families. To do this you need to determine the probability
of different combinations of boys and girls. What are the probabilities of having the
following combinations of boys and girls in families with seven children?
a) 6 boys and 1 girl
b) 4 boys and 3 girls
c) 2 boys and 5 girls
d) 0 boys and 7 girls
e) Would your answer to 3b change if the 4 boys and 3 girls had to be born in a specific
order? How would it change and briefly say why it would change.
4. You are studying alleles for a gene that controls self-incompatibility in the rapeseed.
There are 8 alleles and all are co-dominant to each other.
a) What does the term co-dominant mean related to gene expression?
b) How many genotypes are possible with the 8 alleles for self-incompatibility?
c) Can you also determine the number of phenotypes possible? Briefly explain your
answer.
2
Name: _____________________________
5. You are asked to do a study in humans to determine the level of genetic control and
environmental control there is for various traits.
a) How would you do this since you are not allowed to do controlled matings to produce
off-spring for a genetics study?
b) With your method what would you expect to see if the trait was?
1) Mostly under genetic control.
2) Mostly under environmental control.
6. You are working with geraniums and discover an odd flower color after mating a red
with a white geranium. The F1 plants were all blue. Thinking you could make money
selling geraniums for federal holidays like the fourth of July you cross the F1 plants
and get the following progeny:
phenotype
Blue
Red
White
no. progeny
531
175
254
960
a) What type of gene action are you observing?
b) Test your hypothesis using Chi square analysis (show your work)
3
Name: _____________________________
7. You are asked to map three genes in wheat that are found on the same chromosome
arm. The traits you are interested in are: tall – T and dwarf – t, red seed – R and
white seed – r, and awnless – A and awned – a. You cross two true breeding parents
to produce completely heterozygous F1 plants. You do a testcross to your F1 plant
using completely homozygous recessive (tt rr aa) plants and recover the following
progeny:
genotype
no. of progeny
TRa
trA
2,200
2,100
TrA
tRa
320
305
Tra
tRA
170
150
TRA
tra
total
20
15
5,280
a) What are the genotypes of the two true breeding parents?
b) What is the gene order?
c) Draw a gene map showing the distance in map units (mu) between the genes.
d) What is the percent interference for these three genes?
4
Name: _____________________________
Part 2 – 18 points – answer 3 of the following 4 questions
8. You are studying a trait in animals and observe something odd when you do
controlled matings. While you know that the trait is not associated with the sex
chromosome its expression in progeny appears to be controlled by whether the male
is donating the trait. If the male donates the trait, all the progeny show it. If the
female donate the trait none of the progeny show it. What could be causing this
difference in expression if the trait is not sex linked? Briefly explain your answer.
9. You are asked to evaluate whether a genetic trait is a recessive lethal in dogs.
a) What matings would you need to make and what deviations from expected Mendelian
ratios would you expect to observe if the trait was a recessive lethal. Briefly explain
the reason for the deviation in the expected Mendelian ratio.
b) How would your results differ if it was a dominant lethal? Briefly explain your
answer.
5
Name: _____________________________
10. In studying a trait in mice you believe you have discovered a recessive sex linked trait
for blue eye color. Thinking blue-eyed mice could be the next pet sensation you
decide to patent the trait but first you need to confirm the trait is sex-linked.
a) What is the name of the cross or crosses you would make to confirm sex-linkage?
b) Diagram the crosses you would make and the progeny you would expect that would
demonstrate the trait was sex-linked.
11. You have been asked to help identify molecular markers to use for diagnosing genetic
disorders in humans. You ask for information related to flanking markers associated
with the trait in question. You are given the following sets of molecular markers and
their corresponding distances (in centa Morgan (CM)) from the gene in question:
Set
1
2
3
4
Marker 1
6 cM
5 cM
3 cM
1 cM
Marker 2
3 cM
4 cM
2 cM
7 cM
a) Why did you want to work with sets of flanking markers?
b) Which set of markers would work best for accurate diagnosis of people carrying the
genetic disorder? Briefly explain your reasoning.
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Name: _____________________________
Formulas
(n!/ w!x!) pwqx
(p + q)n = 1
n(n + 1) / 2
3n
 (ob - ex)2/ex
((sco + dco)/total) x 100
sco freq1 x sco freq2 x total progeny
1 - (ob dco/exp dco)
df = (n-1)
df
.05
1
2
3
3.84
5.99
7.82
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