name:_______________________
student ID:_____________________
Genetics L311 exam 2
October 16, 2015
Directions: Please read each question carefully. Answer questions as concisely as possible. Excessively
long answers, particularly if they include any inaccuracies, may result in deduction of points. You may
use the back of the pages as work sheets, but please write your answer in the space allotted. However,
you must show all your work. Clearly define your genetic symbols. We will not make guesses as to
what a particular symbol is intended to mean. Also, don’t assume that strains are true-breeding unless
this is stated in the question. Finally, show all your work. Good luck.
page 2
_______
(20 points possible)
page 3
_______
(25 points possible)
page 4
_______
(21 points possible)
page 5
_______
(22 points possible)
page 6
total
(12 points possible)
_______ (of 100 points possible)
1
name:_______________________
student ID:_____________________
1. Short answers (2 points each, 20 points total)
A. A(n) conservative mutation leads to production of a protein in which one amino acid is
replaced by a biochemically similar one.
B. A(n) prion is an infectious particle composed of protein that is capable of producing a
transmissible disease. Examples produce scrapie in sheep or Creuzfeldt-Jakob disease in
humans.
C. Densely staining, compact and relatively transcriptionally inactive regions of chromosomes
are referred to as heterochromatin .
D. Based on the position of its centromere, this chromosome is said to
be acrocentric .
E. Reversion or reverse mutation is the conversion of a mutation back to wild type.
F. A heritable state of gene function not encoded within the DNA is referred to as epigenetics .
G. Linkage is the tendency for genes located on the same chromosome to be inherited
together.
For the following, please provide a brief definition of the term given:
H. suppression: When one mutation masks the effect of a second, restoring the phenotype
to wild type.
I. telomerase: The enzyme that extends the length of telomeres.
J. kinetochore: This is the centromere plus associated proteins. It provides several
important functions including mediating the attachment of chromosome to spindle.
2
name:_______________________
student ID:_____________________
2. The hypothetical three-eyed cicada has been found in several true breeding strains. One has blue
wings and long antennae. The second has red eyes. You cross blue-winged, long antennaed X red eyed
and find the progeny all have all wild type phenotypes (i.e. not blue winged, long antennaed or red
eyed). You test cross the F1’s and find the results shown below. Recessive phenotypes are listed below
123
4513
118
19
125
4781
21
134
long antenna, blue wing, red eyed
long antenna, blue wing
blue wing, red eyed
long antenna, red eyed
long antenna
red eyed
blue wing
wild type
A. What do the results shown above say about the chromosomal location of the three genes (4
points)? All three genes are linked.
B. Please calculate the genetic distance between all of the linked genes, if any are linked. If not
linked please describe how you reached that conclusion. Please show your work (9 points).
b-l: (118+125+19+21)/9834X100 = 2.8 cM
l-r: (123+134+19+21)/9834X100 = 3.0 cM
b-r: 28.8+30.2 = 5.9 cM
3. You find a rare toad, S. myersae, in the sand dunes of Northern Indiana. This species normally has
gray spots but some individuals have white spots. You cross the following true breeding strains
together and get these results:
Cross 1: Gray spot male X white spot female  all offspring have white spots
Cross 2: Gray spot female X white spot male  all offspring have gray spots
Cross 3: White spotted males from cross 1 X gray spotted females from cross 2  1/2 gray and
1/2 white
A. What mode of inheritance explains these results (4 points)?
This gene seems to be paternally imprinted
B. If a toad inherited a nonsense mutation that knocked out gene function in the paternal copy of the
gene and wild type from mom, what phenotype would the offspring show (4 points)?
Gray or wild type
C. If a toad inherited a nonsense mutation that knocked out gene function in the maternal copy of the
gene and wild type from dad, what phenotype would the offspring show (4 points)?
White or mutant
3
name:_______________________
student ID:_____________________
4. Two recessive mutations have been identified in the California grasshopper, S. ydeae. r causes red
stripes and b causes blue legs. Recombination mapping is performed by crossing r b / ++ females with
r b / r b males. Four distinct classes of progeny are produced.
156
45
41
160
402
Red stripes, blue legs
red stripes
blue legs
wild type
A. What is the map distance between the r and b genes (4 points)?
(45+41)/402 X 100 = 21.4 cM
B. In another experiment, a male heterozygous for both mutations in cis is crossed with a female
heterozygous for both mutations in trans. What fraction of offspring will be genotypically homozygous
wild type for both genes (7 points)?
(0.393)(0.107) = 0.042 or 4.2%
5. You are attempting to determine if two genes in the Bornean horned beetls, uni (which causes
beetles to grow extra long horns) and stp (which causes beetles that are normally stippled to be all
black) are linked. You cross a heterozygote with homozygous recessive to get the following results.
412 black, long horned
363 black
368 long horned
405 wild type
A. Please state the null hypothesis that you will test (2 points).
Null hypothesis: The two genes are not linked.
B. Please calculate chi square. Using the table at the right, what is the probability that your null
hypothesis is incorrect? What can you conclude (8 points)?
(817 – 774)2/774 + (731-774)2/774
= 4.78
Probability of result being due to chance is
between 0.5 and 0.01 so the probability that the
null hypothesis is incorrect is greater than 0.95.
We reject the null hypothesis and conclude that
the genes are linked.
4
name:_______________________
student ID:_____________________
6. You discover two unusual true-breeding strains of the iridescent goliath bettle, A millerae. One is
green and the other is blue. A cross of true-breeding green X true-breeding blue produces all green. A
cross of green F1 X green F1 produces the following:
207 green
17 blue
50 purple
A-B- and A-bb (or aaB-)
aabb
aaB- (or A-bb)
A. Please give the genotypes of the F2’s on the lines provided above (8 points).
B. What is the probability that if you choose a green beetle at random, it would be homozygous for all
of the genes (4 points)?
AABB and are homozygous for each gene
AAbb
1/3(1/4) + 1/3(1/4) = 1/6
7. In the rare mountain rattlesnake, J. mannae, most of the animals have dull scales whereas a
recessive mutation in sh produces shiny scales and most have black scales whereas a recessive
mutation in gr produces pale gray. One unusual mountain rattlesnake is mostly wild type (i.e. dull
scaled and black) but has a small patch with shiny, gray scales. Please name and diagram a process that
might produce this (10 points).
This is mitotic recombination.
Could also come from mitotic
sh +
nondisjunction or chromosome
loss.
gr +
sh sh + +
+
gr gr + +
+
sh +
d
gr +
+
sh
d
gr
+
+
sh
d
gr
t+
+
+
+
5
name:_______________________
student ID:_____________________
8. You’ve identified a new food sweetener, that you call sweeties. Before selling it to food producers
you test it via the Ames test to be sure it’s not mutagenic. You use two strains of Salmonella, strains 1
and 2, which contain a frameshift mutation or a base substitution, respectively, in a gene required for
histidine biosynthesis. You find the results pictured below (all plates contain only enough histidine to
permit a few cycles of cell division. A spot indicates formation of a colony of cells.)
A. Why did you include strains 1 and 2 incubated without the suspected mutagen? Why are
there a few colonies on each of those plates (3 points)?
To check for spontaneous mutations.
B. Is sweeties safe to add to the food supply? If it can alter DNA, what type of mutation does it
cause (3 points)?
No, it seems to cause base alterations.
C. If you found the results shown below using sweeties that was not incubated with liver
extract, what would you conclude (3 points)?
This would suggest that liver enzymes convert sweeties to a mutagen, and that in the
absence of liver enzyme it is not mutagenic.
D. Why did you add enough histidine to permit only a few rounds of cell division (3 points)?
Some mutagens, such as base analogs, require replication.
6