Problem Set 3, Spring 2016
8 points total
Note: Please show all work.
Student Name:
1. Cystic fibrosis (CF) is an autosomal recessive disorder. Normally, both parents must be
carriers of the CF gene in order for the child to inherit the disorder. In 1998, Arthur Beaudet of
the Baylor College of Medicine saw a very unusual CF patient. Testing revealed the following:
1) the mother was a CF carrier
2) the father had two wild-type alleles
3) both of the patient's chromosomes that contained the CF gene had come from her
mother.
It was determined that nondisjunction must have occurred in both oogenesis of the mother
and spermatogenesis of the father to create the patient's odd combination of alleles. Diagram
the 2 nondisjunction events that occurred in meiosis of the father and of the mother. Then
show which two gametes fused to produce the CF patient's phenotype.
2. A man has an extra toe on each foot as a result of a dominant trait that he inherited from his
mother. His mother's mother and his mother also had the trait. The man falls in love with a
ten-toed beauty and their first child, a boy, has a normal number of toes.
A. Draw a pedigree for this family and show all genotypes.
B. What is the chance that their next child will have 12 toes like it's father?
1
Problem Set 3, Spring 2016
8 points total
Student Name:
3. In the pedigree shown, individual III-1 died at age 2 of a rare metabolic disorder.
A. What is/are the possible modes of
inheritance?
I
1
2
3
4
II
B. Indicate the genotypes of each individual
in the pedigree, based on the pattern of
inheritance you listed in part A (if you
III
listed more than one, choose your favorite)
1
1
2
2
3
4. A rare disease affects individuals as shown. From the pedigree, this trait is most likely to be
inherited as an
autosomal dominant or
X-linked dominant trait.
Assign genotypes to all
individuals for each
pattern of inheritance. If
multiple genotypes are
possible, please list
them all.
2
Problem Set 3, Spring 2016
Student Name:
8 points total
5. Joe is colorblind. Colorblindness is X-linked and recessive. His wife Susie has normal vision
with no family history of the disease. What are the chances of their having a colorblind son?
Daughter? Can any of their children be carriers? If so, what proportion and what gender(s)?
6. While studying guinea pigs in South America, you notice that there are two true breeding
populations in your area. One has long hair and light eyes, and the other has short hair and
dark eyes. You cross guinea pigs from population 1 with population 2. The F1 progeny all have
long hair and dark eyes. You cross the F1 progeny to produce F2's and obtain the following
results:
308 long hair, light eyes
901 long hair, dark eyes
287 short hair, dark eyes
104 short hair, light eyes
1600 total
A. What are the genoytpes of the F2 guinea pigs?
B. If you cross long-haired, light-eyed F2 progeny with short-haired, light-eyed F2
progeny, what is the probability of obtaining short-haired, light-eyed offspring? What is
the probability of obtaining long-haired, dark-eyed offspring?
7. The genetic disorder citronosis makes people crave grapefruit. Results of a pedigree analysis
of citronosis are shown below:
3
Problem Set 3, Spring 2016
8 points total
Student Name:
I
1
2
II
1
2
3
4
6
5
III
1
2
3
4
5
6
7
A. What is the most likely pattern of inheritance for citronosis?
B. List the most likely genotype for the following individuals:
I-1
II-2
III-2
III-5
8. After studying a lizard species on a Pacific island, you conclude that there are two truebreeding strains: strain A is green and has a spikey tail and strain B is blue and has a smooth
tail. A cross between a female of strain A and a male of strain B produces all green, smoothtailed offspring. A cross between the F1's results in the following progeny at the frequencies
indicated.
Green, smooth-tailed females
Green, smooth-tailed males
Blue, smooth-tailed males
Green, spikey-tailed females
Green, spikey-tiled males
Blue, spikey-tailed males
3/8
3/16
3/16
1/8
1/16
1/16
A. What are the genotypes of the original strains and what are the genotypes of the F2
progeny?
4
8
Problem Set 3, Spring 2016
8 points total
Student Name:
B. What phenotypes will offspring have from a cross of blue, spikey-tailed F2 males
with original strain B females?
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