Problem Set #4
Van Den Bussche
Fall 2004
1. Use the following two-point recombination data to map the genes concerned. Show the order
and the length of the shortest intervals.
loci
a,b
a,c
a,d
a,e
b,c
% recombination
50
15
38
8
50
loci
b,d
b,e
c,d
c,e
d,e
% recombination
13
50
50
7
45
2. A phenotypically wild-type female fruit fly that was heterozygous for autosomal
genes controlling body color and wing length was crossed to a homozygous mutant male
with black body (allele b) and vestigial wings (allele vg). The cross produced the
following progeny: 126 wild type body and wings, 24 wild-type body and vestigial
wings, 26 black body and wild-type wings, 124 black body and vestigial wings. (a) What
is the recombination frequency? (b) Diagram the cross, showing the arrangement of genes
on the chromosomes of the male and female crossed to produce these offspring.
3. Assume that genes A and B show 20 percent crossing-over. If a homozygous AB / AB
individual is crossed with an ab / ab individual, (a) What will be the genotype of the F1?
(b) What gametes will the F1 produce and in what proportions? (c) If the F1 is testcrossed
with a doubly homozygous recessive individual, what will be the proportions and
genotypes of the offspring?
4. Using the information above except that the original cross is Ab / Ab X aB / aB, (a) what
will be the genotype of the F1? (b) What gametes will the F1 produce and in what
proportions? (c) If the F1 is testcrossed with a double homozygous recessive, what will be
the proportions and genotypes of the offspring?
5. Genes d and p occupy loci 15 map units apart in the same autosomal linkage group. Gene h
is a separate autosomal linkage group and therefore segregates independently of the other
two. What types of offspring are expected, and what is the probability of each when and
individual of genotype dP / Dp H/h is testcrossed?
6. Genes A and B are in one chromosome 40 m.u. apart; C and D are in another chromosome, 10
m.u. apart. Genes E and F are in yet another chromosome and are 60 m.u. apart. Cross a
homozygous ABCDEF individual with an abcdef one, and cross the F1 back to a
homozygous abcdef individual. What is the probability of getting and individual of
phenotype AbcDEf?
7. A Drosophila geneticist made a cross between females homozygous for three X-linked
mutations (y, yellow-body; ec, echinus eye shape; w, white eye color) and wild type
males. He then mated the F1 females to triply mutant males and obtained the following
results.
Females
Males
+ + + / y ec w
y ec w / y ec w
y + + / y ec w
+ ec w / y ec w
y + w / y ec w
+ ec + / y ec w
+ + w / y ec w
y ec + / y ec w
+ + +
y ec w
y + +
+ ec w
y + w
+ ec +
+ + w
y ec +
Number
475
469
8
7
18
23
0
0
a. What is the genotype of the triply heterozygous female used to produce the F1. Be sure
to draw the genotype using standard notation and to make it clear whether the
configuration of alleles is cis or trans.
b. Draw a chormosome map indicating proper gene order and distance between each pair
of genes.
8. Assume in Drosophila there are three genes, x, y, and z, with each mutant allele recessive to
the wild-type allele. A cross between females heterozygous for these three loci and wildtype males yieded the following progeny:
Females:
+ + +
Males:
+
+
+
x
x
x
+
+
y
+
y
y
+
z
z
+
+
z
1010
39
430
32
27
441
31
a. Construct a linkage map of the three genes, indicating correct gene order and distance
between each pair of genes.
b. Calculate Interference for this cross.
The following tetrad data were obtained from the cross of A B X a b in Neurospora:
Spore Pairs
Top of
ascus
Bottom of
ascus
(1,2)
(3,4)
(5,6)
(7,8)
A
a
a
A
A
a
A
a
a
A
a
A
a
A
A
a
Number of
tetrads
61
55
40
44
Total = 200
9. What is the distance between the A locus and its centromere?
10. A cross between a pink (p-) yeast strain of mating type mt+ and a grey straini (p+) of mating
type mt- produced the following tetrads:
Number of tetrads
18
8
45
Kind of tetrad
p+ mt+, p+ mt+, p- mt-, p- mtp+ mt+, p- mt+, p+ mt-, p- mtp+ mt-, p+ mt-, p- mt+, p- mt+
a. On the basis of these data, are the p and mt genes on separate chromosomes?
b. If the p and mt genes are on the same chromosome, what is the map distance between
them?
Answer Sheet: Only turn in your answer sheet. You should keep the questions to help when we cover the questions in class.
Answers are due before the beginning of class on Friday 17 September 2004. Alternatively, answers may be slid
under my office door (LSW 411) prior to September 17. Answers turned in after the start of class on Monday (9-1704) will not be given credit.
NAME:
1.
2a.
2b.
3a.
3b.
3c.
4a.
4b.
4c.
5.
6.
7a.
7b.
8a.
8b.
9.
10.