Problem Set 4, Spring 2016
8 Points Total
Student Name:
1. A cross between a purebred black mouse and a purebred white mouse yields all black F1 offspring.
These black F1 sibling mice are crossed to produce an F2 generation. You observe the following F2
phenotypic ratio:
White: 22
Black: 175
Gray: 114
a. Draw out the crosses described above, showing the genotypes of the parents, F1 and F2.
b. You cross white mice from the F2 generation X black mice from the F2 generation. What is
the probability of getting black offspring from this cross?
2. You cross a purebred red-eyed mouse with a purebred yellow-eyed mouse and you get all redeyed F1s. When you then self the F1s you get an F2 generation composed of the following: 17 yellow
eyes, 207 red eyes, and 50 blue eyes.
a. Give the genotypes of F1 and F2; i.e. draw out the cross.
b. What is the simplified ratio?
c. How does this ratio arise?
3. A male fruitfly with curly wings is crossed to a female with normal wings. You next cross curly
male F1's X curly female F1's to yield the F2's shown below.
F1: (from curly wing male X
F2 (from curly male F1 X
normal wing female)
males curly female F1):
1/4 normal males
1/3 curly males
1/4 normal females
1/3 curly females
1/4 curly males
1/6 normal males
1/4 curly females
1/6 normal females
a. Diagram the cross of F1’s that produced the F2 progeny shown. Also show the genotypes of
the F1's and F2's. Define your choice of symbols.
1
Problem Set 4, Spring 2016
8 Points Total
Student Name:
b. Suggest a mode of inheritance that explains the above ratios (i.e. dominant, recessive, xlinked, autosomal, etc.)
4. There are two naturally occurring strains of the octopus, T. bastinae, those with short tentacles and
blue spots and those with long tentacles and yellow spots. You cross a true-breeding short tentacle,
blue spotted octopus and a true-breeding long tentacled, yellow spotted octopus. The F1’s all have
long tentacles and green spots. You cross the F1’s amongst themselves and find the following F2’s:
3/16 long tentacle, yellow spotted
1/16 short tentacle, yellow spotted
6/16 long tentacle, green spotted
2/16 short tentacle, green spotted
3/16 long tentacle, blue spotted
1/16 short tentacle, blue spotted
a. What is the genotype of each of the F2 progeny?
b. If you cross short tentacle, blue spotted F2 by short tentacle, green spotted F2, what will the
offspring look like?
5. In the jungles of Jamaica lives a colorful species of beetle, K. badgerae. Three strains of K. badgerae
are known. Strain 1 has red wing covers, strain 2 has orange wing covers and strain 3 has green wing
covers. You take members of each strain back to the lab and perform the following crosses, which
yield the results shown.
strain 1 X strain 2:
strain 1 X strain 3:
strain 2 X strain 3:
all green
1/2 red and 1/2 green
1/2 orange and 1/2 green
a. What are the genotypes of the three strains?
strain 1 ______
2
Problem Set 4, Spring 2016
8 Points Total
Student Name:
strain 2 ______
strain 3 ______
b. What phenotypes do you expect from a cross of strain 3 X strain 3? Please include the
relative frequencies of each phenotype.
6. You discover a new substance (Substance E) that is involved in the production of zigzag stripes.
You are interested in understanding the genetic basis for substance E synthesis, and therefore used a
genetic screen to identify 8 mutations (numbered 1 – 8) that prevent substance E synthesis. You cross
homozygous recessive parents in all possible pairwise combinations to generate the results presented
in the table.
1
2
3
4
5
6
7
8
1
+
+
+
+
+
2
+
+
+
+
+
-
3
+
+
+
+
+
4
+
+
+
+
+
5
+
+
+
+
+
+
+
6
+
+
+
+
+
-
7
+
+
+
+
+
+
+
8
+
+
+
+
+
-
a. What is the name for this type of cross and what type of information does it provide?
b. How many genes are involved in the production of Substance E?
c. Show which mutations belong to each gene, and give each gene a symbol.
d. Shown below is the biochemical pathway leading to production of substance E. You assay for
each of the intermediates in each of the eight mutants. A + means that the compound was
detected in mutant cells whereas a – indicates that it was not. Write above each arrow the gene(s)
that encode the enzyme(s) responsible for that step of substance E synthesis.
mutants
3
Problem Set 4, Spring 2016
8 Points Total
A
B
C
D
E
1
+
+
+
A
2
+
-
3
+
+
+
-
4
+
+
+
-
5
+
+
+
+
B
Student Name:
6
+
-
7
+
+
-
8
+
C
D
Substance E
7. During your investigations of frog species in Costa Rica you find two strains of the splendid poison
dart D. webbae. Strain 1 has yellow bodies and red eyes. Strain two has blue bodies and white eyes.
You cross strain 1 females with strain 2 males. The resulting F1's all have green bodies and red eyes.
You cross F1's to produce the following F2's at the frequencies indicated:
1/4 green-bodied, red-eyed females
1/8 yellow-bodied, red-eyed females
1/8 blue-bodied, red-eyed females
1/8 green-bodied, red-eyed males
1/8 green-bodied, white-eyed males
1/16 yellow-bodied, red-eyed males
1/16 yellow-bodied, white-eyed males
1/16 blue-bodied, red-eyed males
1/16 blue-bodied, white-eyed males
a. Please give the genotypes of the F2 animals in the space provided.
b. Please give the genotypes, phenotypes and expected frequencies of the different classes of
offspring that would result from a cross of green-bodied, red-eyed males X yellow-bodied, red
eyed- females.
4
Problem Set 4, Spring 2016
8 Points Total
Student Name:
8. While researching methods of year-round farming, you isolate 6 independent mutations that allow
soybeans to withstand freezing. All 6
lines were intercrossed, and you obtain
1
2
3
4
5
6
the following results (+ indicates wild
1
–
+
+
–
+
+
type plants, – indicates cold resistant):
2
+
–
+
+
+
+
A. What is the name of this type
of test?
3
4
5
6
+
–
+
+
+
+
+
+
–
+
–
+
+
–
+
+
–
+
–
+
+
+
+
–
B. How many individual genes
were identified? Which
mutations are allelic?
C. In further studies, mutation #7 is also found to cause resistance to freezing. It is determined
that mutations #2 and 7 are allelic. Add the complementation test results in the space provided
in the chart above.
5