1. On a chicken farm, walnut-combed fowl that were crossed with each other
produced the following offspring: walnut-combed, 87; rose-combed, 31;
pea-combed, 30; and single-combed, 12. If we hypothesize that inheritance of
comb type is by two loci, and the results of the cross of dihybrids produce fowl
with the four comb types in a 9:3:3:1 ratio of walnut-, rose-, pea-, and
single-combed fowl, respectively. Do the data support the hypothesis?
Degrees of
Freedom
Probabilities
0.99
0.95
0.80
0.50
0.20
0.05
0.01
1
2
3
4
5
0.000
0.020
0.115
0.297
0.554
0.004
0.103
0.352
0.711
1.145
0.064
0.446
1.005
1.649
2.343
0.455
1.386
2.366
3.357
4.351
1.642
3.219
4.642
5.989
7.289
3.841
5.991
7.815
9.488
11.070
6.635
9.210
11.345
13.277
15.086
2. Consider the following crosses involving yellow and gray true-breeding
Drosophila:
Cross
F1
F2
Gray female × Yellow male
all male gray, all females gray
97 gray females, 42 yellow
all female gray, all males yellow
?
males, 48 gray males
Yellow female × gray male
a. Is color controlled by an autosomal or X-linked gene?
b. Which allele, gray or yellow, is dominant?
c. Assume 100 F2 offspring are produced in the second cross. What kinds and
what numbers of progeny do you expect? List males and females separately.
3. The following three recessive markers are known in lab mice: h, hotfoot; o, obese;
and wa, waved. A trihybrid of unknown origin is testcrossed, producing the
following offspring:
Hotfoot, obese, waved
357
Hotfoot, obese
74
Waved
66
Obese
79
Wild-type
343
Hotfoot, waved
61
Obese, waved
11
Hotfoot
Total
9
1000
a. If the genes are linked, determine the relative order and map distances
between them.
b. What was the cis-trans allele arrangement in the trihybrid parent?
c. Is there any crossover interference? If yes, how much?
4. A strain of yeast requiring both tyrosine (tyr-) and (arg-) is crossed to the wild-type.
After meiosis, the following ten asci are dissected. Classify each ascus as to
segregational type (PD, NPD, TT). What is the linkage relationship between
these two loci?
1
2
3
4
5
6
7
arg- tyr- arg+ tyr+
arg+ tyr+ arg+ tyr+
arg- tyr+ arg- tyr+
arg- tyr- arg- tyrarg- tyr- arg- tyr+
arg+ tyr+ arg+ tyr+
arg- tyrarg+ tyr+
arg+ tyr+ arg- tyrarg- tyr- arg- tyrarg+ tyr - arg+ tyrarg+ tyr+ arg+ tyr+
arg+ tyr- arg+ tyr+
arg- tyr- arg- tyrarg- tyr+ arg+ tyr -
8
9
10
arg+ tyr+
arg+ tyr+
arg- tyr-
arg- tyr- arg- tyrarg- tyr- arg+ tyr+
arg+ tyr+ arg- tyr-
arg+ tyr+
arg- tyrarg+ tyr+
5. The following shows the growth (+) or lack of growth (-) of various mutants in
another biosynthesis pathway. Determine this pathway, the point of blockage for
each mutant, and the substrate each mutant accumulates.
Additives
Nothing
A
B
C
D
E
1
_
_
_
_
_
+
Mutants
2 3 4
_ _ _
+ + +
+ _ +
+ _ +
_ _ +
+ + +
5
_
+
_
+
_
+
6. You have four strains of Drosophila (1-4) that were isolated from different
geographic regions. You compare the banding patterns of the second
chromosome and obtain these results (each letter corresponds to a band):
(1) mnrqpostuv
(2) mnopqrstuv
(3) mnrqtsupov
(4) mnrqtsopuv
If (3) is presumed to be the ancestral strain, in what order did the other strains arise?
7. Deduce whether each of the nucleic acid molecules in the following table is DNA
or RNA and single-stranded or double-stranded.
Nucleic
Acid
Molecule
A
B
C
D
E
F
%A
%G
%T
%C
%U
33
33
26
21
15
30
17
33
24
40
40
20
33
17
0
21
0
15
17
17
24
18
30
20
0
0
26
0
15
15
8. What is a consensus sequence? a conserved sequence?
9. Define structural and functional alleles. What is the cis part of a cis-trans
complementation test?
10. A plasmid was isolated and treated with several restriction enzymes. The
fragment lengths were determined for each digest. From the data below,
determine the restriction map for this plasmid. Include the restriction sites and
fragment lengths in your diagram.
EcoRI: 1.7, 0.8
BamHI: 1.3, 1.2
EcoRI+ BamHI: 1.2, 0.7, 0.5, 0.1
EcoRI+ SmaI: 1.4, 0.8, 0.3
BamHI + SmaI: 1.2, 0.9, 0.4