Problem Set 9, Fall 2015
Name:
8 points total
1. In a newly discovered species of slug, two different phenotypes are observed: blue spots (+) and purple
sports (p).
cross 1
purple female x blue male

all purple
 cross siblings
all blue
 cross siblings
blue and purple
cross 2
blue female x purple male

all blue
 cross siblings
all blue
 cross siblings
blue and purple
Name and describe the type of inheritance determining spot color in these slugs.
This looks like maternal effect. It’s not extranuclear because all of the offspring would show the purple
phenotype under cross 1 and the blue phenotype under cross 2 in each generation. It’s also not genomic
imprinting.
What phenotypic ratio is observed in the F3 generations?
3 blue: 1 purple
2. Here is the pedigree of a rare genetic
disorder. Assume that individuals who
marry into the pedigree do not carry the
trait (except as shown).
Name and describe the type of
inheritance exhibited in this pedigree.
This looks like extranuclear
inheritance. Genomic imprinting is
possible but not likely because if it
was paternally imprinted then we
would expect only half the offspring
of affected females to be affected.
Problem Set 9, Fall 2015
Name:
8 points total
3. In a newly discovered species of sexually-reproducing money tree, you discover that 5 dollar bill (db+)
producing trees are dominant to 10 dollar bill producing trees (db-). The following crosses yield the outcomes
shown.
10 dollar bill females x 5 dollar bill males
F1
all 10 dollar bill
cross siblings
F2
all 5 dollar bill
cross siblings
F3 5 dollar bill and 10 dollar bill
a. What is the mode of inheritance?
maternal effect
b. What is the phenotypic ratio in the F3 generation?
3 $5:1 $10
c. Why couldn’t it be either of the other two non-mendelian methods of
inheritance?
Extranuclear inheritance would produce all $10 in the F2. Imprinting
would produce ½ $5 and ½ $10.
4. In a transduction mapping experiment, you get the following result
Experiment
selected marker
unselected marker
+
1
a
45% b+, 5% c+
+
2
b
40% a+, 10% c+
Draw the relative position of a, b, and c.
Problem Set 9, Fall 2015
Name:
8 points total
5. You join a Tollan research group on planet Tollana in studying a gene called green which causes green eyes
instead of blue in a native insect species. This is very important research as the rare green-eyed individuals are
believed to hold special medicinal properties. You know that green is not dominant.
You perform the following crosses to gain insight into the green mode of inheritance:
green-eyed ♀ x blue-eyed ♂
all green-eyed
(cross siblings)
all green-eyed
a. What possible mode(s) of inheritance does eye color exhibit?
extranuclear
b. In a different species of insects you find that there are no maternally inherited organelles. However, you do
see organelles that are inherited strictly from a father. A wild-type organelle is required for large wings.
What happens if you cross a large-winged female with a small-winged male? Draw the crosses for enough
generations to make it clear that this is extranuclear inheritance. Assume that you are crossing siblings after the
first cross.
By F2 generation
you can
distinguish
between these
possibilities.
What happens if you do a cross reciprocal to the one above? Once again, draw the crosses for enough
generations to make it clear that this is extranuclear inheritance.
Have to carry
crosses to F3 to
distinguish
between these
possibilities. (in
both cases the F2
are wild type)
6. In a transduction mapping experiment, you get the following results:
Problem Set 9, Fall 2015
Name:
8 points total
When you select for presence of wt gene X, you find that gene Y cotransduces 47% of the time, and gene Z
cotransduces 3% of the time. When you select for presence of wt gene Z, you find that gene X cotransduces 5%
of the time and you never see gene Y cotransduce with gene Z. What are the relative map positions of genes X,
Y, and Z?
7. In the rare musical lemurs of Madagascar, K. badgerae, you observe two distinct phenotypes: golden fur and
brown fur. To study the transmission of this trait you obtain permission from the Madagascar government to
collect a few animals and perform crosses that yield the results shown below.
Golden female X Brown male
All Golden
Cross siblings
All Golden
Cross siblings
Golden and Brown
A. Name and describe the type of inheritance determining the fur color in these lemurs (6 points). This looks
like a maternal effect gene controls fur color. In maternal effect, the mother’s genotype determines the
offsprings phenotype through factors deposited in the egg either as RNA or protein.
B. What phenotypic ratio is observed in the F3 generations (4 points)?
3:1
8. You are attempting to find the map distance between two genes in a specific species of phage. The r+ gene
is responsible for large plaques, and r- is responsible for small plaques. The b+ gene gives a bluish color to the
plaques, while b- makes them clear.
a. How would you perform this phage recombination mapping experiment in order to determine the
distance between the two genes?
Infect relatively few bacterial cells with many phage, then add more cells, spread on plate and
examine plaques after they’ve had time to grow.
b. After plating out the infected cells, you find the following:
4 large, blue plaques
r+ b+
5 small, clear plaques
r– b–
36 large, clear plaques
r+ b–
38 small, blue plaques
r– b+
What are the genotypes of these plaques? What are the genotypes of the original phage?
Originals are r+b– and r–b+
c. What is the recombination frequency between the r and b genes in this species of phage?
(4 + 5)/(4 + 5 + 36 + 38) = 9/83 = 0.11