Download Genetics L311 exam 1

name:_______________________
student ID:_____________________
Genetics L311 exam 1
September 16, 2016
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 and please 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 truebreeding unless this is stated in the question. Finally, show all your work. Good luck.
page 2
_______
(20 points possible)
page 3
_______
(26 points possible)
page 4
_______
(15 points possible)
page 5
_______
(21 points possible)
page 6
_______
(18 points possible)
total
_______ (of 100 points possible)
1
name:_______________________
student ID:_____________________
1. Short answers (2 points each, 20 points total)
A. The somatic
cells.
cells make up most of the body. These are all the cells except for the germ
B. Nondisjunction provided proof for many that the genes must be on the chromosomes.
C. Haploinsufficient is when having a single wild-type copy of a gene is not enough to
prevent a mutant phenotype.
D. Chiasmata are the apparent points of crossing over.
E. Different versions of a gene are called alleles .
F. Pleiotropy is when mutation of a single gene produces multiple phenotypes.
G. The region found on both the X and Y chromosomes is called the pseudoautosomal .
For the following, please provide a brief definition of the term given:
H. hemizygous: Having only one copy of a chromosome or portion of a chromosome.
I. polar body: Meiotic products of oogenesis. These are small cells that are used to dispose of
extra copies of chromosomes while still leaving a single, haploid cell with plenty of
cytoplasm.
J. test cross: Cross of unknown genotype X homozygous recessive.
2
name:_______________________
student ID:_____________________
2A. What is the most likely mode of transmission of the trait segregating in the family shown below (4
points)?
autosomal recessive
B. Obligate carriers are individuals who must carry
the mutation that produces the trait. Please list the
obligate carriers in the pedigree at right (4 points).
I-1, I-2, III-2, III-3, III-5, III-6
C. What is the probability that IV-3 carries the
mutation (i.e. is heterozygous, 3 points)?
1/2
D. Please provide the genotoypes of the following (3 points):
I-1 Aa
II-5 A–
III-7 A–
3. The mythical deep sea angler, N. rajovicae, is found in isolated populations with a few characteristic
differences. Some have long fins whereas others have short fins and some have large scales whereas
others have small scales. Presented below are the results of several crosses (12 points).
Parental
1
2
3
4
Long fins, small scale X short fins, small scale
Long fins, large scale X short fins, small scale
Long fins, large scale X long fins, large scale
Short fins, large scale X short fins, large scale
Long fins,
large
scales
0
103
451
0
Long fins,
small
scales
181
98
0
0
Please provide the genotypes of the parental mice for each cross.
Long fins, small scale X short fins, small scale
Llss X llss
Long fins, large scale X short fins, small scale
LlSs X llss
Long fins, large scale X long fins, large scale
LlSS X LlSS
Short fins, large scale X short fins, large scale
llSs X llSs
3
Short fins,
large
scales
0
101
158
358
Short fins,
small
scales
178
99
0
121
name:_______________________
student ID:_____________________
4. A species of deep-sea yellow sponge has somatic cells containing 3 pairs of chromosomes, one long,
one medium and one short. The gene conferring yellow color (Y) is on the long chromosome, a gene (B)
that controls behavior leading to some individual’s predilection for wearing square pants is on the
medium chromosome and a gene (L) causing obsessive laughter is on the short chromosome.
A. A single somatic cell from an individual, named Bob, who is heterozygous for the yellow and
laughter genes and homozygous dominant for B undergoes mitosis. Please draw the products of this
division, including the genes (6 points).
L
B
Y
B
y
B
l
L
B
Y
y
l
B. Please diagram one of Bob’s cell in metaphase II. Include the genes and circle one pair of sister
chromatids. Assume no cross overs (5 points).
L
C. Rarely meiosis can go awry. Please show the products of meiosis I and meiosis II (you need not
include all the steps of each division, just the products) where nondisjunction of the long chromosome
during meiosis I has occurred. Meiosis II was normal. Show all chromosomes. You do not need to
include the genes in your answer (5 points).
4
name:_______________________
student ID:_____________________
5. A newly discovered species of deep-sea squid, E. qinae, is found to have two true breeding strains.
Strain A has yellow skin and long tentacles, while Strain B has blue skin and short tentacles. A cross of
males from Strain A and females from Strain B results in offspring that all have blue skin and medium
tentacles. Crossing the F1 animals results in the following:
252 blue, medium tentacled females XBXB or b Tt
122 blue, medium tentacled males
XBY Tt
126 yellow, medium tentacled males XbY Tt
128 blue, long tentacled females
XBXB or b TT
60 blue, long tentacled males
XBY TT
65 yellow, long tentacled males
XbY TT
120 blue, short tentacled females
XBXB or b tt
63 blue, short tentacled males
XBY tt
66 yellow, short tentacled males
XbY tt
1002
A. Fill in the genotypes of the F2 progeny (9 points).
B. If you cross blue-skinned, long-tentacled F2 males by F1 females, what fraction of male offspring will
have blue skin and medium tentacles (4 points)?
XBY TT X XBXb Tt => ½ will have blue skin and ½ of those will have medium tentacles to
answer is ¼
6. During your explorations of the sea, you find an interesting starfish that grows short spines instead of
the long spines characteristic of the species. Intrigued you perform a cross of short-spined (i.e. mutant)
X long-spined (i.e. phenotypically wild type) starfish and get the F1 results below. You then cross shortspined F1 amongst themselves to produce the F2’s shown below.
F1s:
½ long spine
½ short spine
ss
Ss
F2s
2/3 short spine
1/3 long spine
Ss
ss
Please provide the genotypes of each of the F1 and F2 animals (8 points)?
5
name:_______________________
student ID:_____________________
7. You discover a population of snails living on a remote Pacific island. The griffins display a variety of
beautifully colored shells. You decide to study the genetic basis for the variation in color. You discover
that all of the variations in color are the result of naturally occurring mutations that alter the normal
brown shell color. You perform a complementation test between 7 of the differently colored animals and
find the results shown in the table.
A. How many genes do mutations 1 through 7
represent (6 points)?
3
B. Mutations 1, 2, 4 and 5 all produce different
shell colors. How can you explain this
phenomenon (4 points)?
Different alleles of the gene produce
different colors (like that rabbit fur color
example in class)
1
2
3
4
5
6
7
1
–
2
–
–
3
+
+
–
4
–
–
+
–
5
–
–
+
–
–
6
+
+
+
+
+
–
7
+
+
+
+
+
–
–
8A. In a population of midnight blooming cactus, you find a single mutation in the gr gene that affects
flower color. The flowers normally appear white, to be more easily seen by night flying moths. A
recessive mutation in gr leads to gray rather than white flowers. You cross homozygous gr mutants and
find the results shown below. No other genes are mutant in these plants. How do you explain these
results (4 points)?
This looks like variable expressivity.
B. In studying a different gene, ebn, you find a similarly puzzling result. When you cross homozygous
ebn mutants (again, wild type is white), you find the results shown below (i.e. the offspring of cactus
homozygous mutant for ebn are either dark blue or white.) No other genes are mutant in these animals.
How do you explain these results (4 points)?
This looks like incomplete penetrance.
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