Download Zoo/Bot 3333

Zoo/Bot 3333
Genetics
Quiz 3
October 31, 2008
For answers to the quiz, please click here:
Questions 1-3 pertain to the following. In the following group of figures, the dotted lines indicate
an area of a chromosome that is inverted relative to normal (solid line) order of genes. Match the
individual chromosome pairs with the statements that follow and give all the correct possibilities.
1
3
2
4
1. An inversion loop would form during meiosis I.
a) 1 and 2; b) 2 and 3; c) 2 and 4; d) 1 and 4; e) none of the above.
2. A single crossover within the inverted region yields four viable gametes.
a) 1 and 2; b) 1 and 3; c) 2 and 4; d) 1 and 4; e) none of the above.
3. A single crossover involving the inverted region on one chromosome and the homologous
region on the other chromosome would yield an acentric fragment.
a) 1 and 2; b) 1 and 3; c) 2 and 4; d) 1 and 4; e) none of the above.
4. A child was born with trisomy 18. When a gene on chromosome 18 was examined in both
parents, the mother was found to be Aa and the father was observed to be aa, while the child was
aaa in genotype. Nondisjunction must therefore have occurred:
a) in the mother; b) in the father; c) you can not tell just on the basis of this data.
5. Deletions can be used to determine the orientation of genes on a chromosome. A series of 5
deletions "uncovered" the following recessive mutations in deletion heterozygotes, allowing them
to show pseudodominance (see p. 496 in Hartwell):
deletion 1:
a,d,e
deletion 2:
c,d,f
deletion 3:
b,c
deletion 4:
d,e
The order of the genes can be represented:
a) abcdef; b) edfacb; c) bcfdea; d) eadfcb; e) adebcf.
6. In fragile X syndrome:
a) females carrying the chromosome have a greater chance for passing the disorder on to their
children than males; b) individuals with over 50 trinucleotide repeats will show mental
retardation; c) there is a linear relationship between the number of trinucleotide repeats and the
severity of the disorder; d) all of the above; e) none of the above.
Questions 7 and 8 pertain to the following. Four E. coli strains of genotype a+b− are labeled 1, 2,
3, 4. Four strains of genotype a−b+ are labeled 5, 6, 7 and 8. The two genotypes are mixed in all
possible combinations and (after incubation) are plated to determine the frequency of a+b+
recombinants. The results indicated in the table are obtained, where M = many recombinants, L
= low numbers of recombinants, and 0 = no recombinants. The strains can be classified as 3
conjugation types: either F−, F+ or Hfr with regard to a and b gene transfer.
strains
5
6
7
8
1
0
L
0
L
2
0
M
0
M
3
L
0
M
0
4
0
L
0
L
7. True or false: The only way that we can get zero recombinants is if an F– strain is crossed to an
F– strain.
8. Which of the following can be classified as Hfr cells?
a) strains 2, 3, 7, 6 and 8; b) strain 2 only; c) strains 2 and 3; d) strains 2 and 7; e) none of the
above.
Questions 9-10 pertain to the following. An Hfr strain of the genotype a+b+c+d+strs is mated
with a female strain of the genotype a-b-c-d-strr. At various times the culture is disrupted in a
blender to separate the mating pairs. The cells are then plated on agar of the following four types
(left table, below), where nutrient A allows the growth of a– auxotrophs, nutrient B allows for the
growth of b– autxotrophs, etc. A (+) indicates the presence of the nutrient or drug, a (-) indicates
its absence.
The table below on the right shows the number of
Timings of Samples Number of Colonies on Agar of Type:
colonies on each type of agar for samples taken
1
2
3
4
at various
0
0
0
0
0
Agar Type Str A B C D times
2.5
0
0
0
0
+ + - + + after the
1
5
15
0
0
0
7.5
104
0
0
0
+ - + + + samples
2
10
215
0
8
0
+ + + - + are
3
12.5
301
6
75
0
15
347
67
150
5
+ + + + - mixed:
4
17.5
20
400
402
104
150
202
205
50
90
25
398
153
203
9. Relative to their proximity to the F factor origin of replication (first gene listed below is
closest) the gene order of these four genes is:
a) a-b-c-d; b) b-a-c-d; c) d-c-a-b;
d) b-d-a-c; e) none of the above.
10. True or false: Gene b is closer to c than a is to c.
90