Homework Assignment II
BIOL2153 Principles of Genetics (Sections 9 & 10)
Due at the beginning of your Discussion Section on Monday, September 29, 2003
Problem 1 (2 pts.): The progeny of a Drosophila female (heterozygous at three mutant loci:
y ct w) crossed to a wild-type male are listed as follows:
females
males
Phenotype
+++
Number
2000
++w
y ct +
y++
+ ct w
+ ct +
y+w
y ct w
+++
773
782
201
209
15
16
3
1
a) On which chromosome do these genes reside?
b) What is the gene order and gene arrangement in the trihybrid female parent?
c) What are the map distances between these genes?
d) Calculate the coefficient of coincidence and the value of interference for this cross.
Problem 2 (2 pts.): A cross in Drosophila involves the recessive, X-linked genes yellow (y),
white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a
male whose eyes and body were normal, but whose wings were cut. The F1 females were wild
type for all three traits, while the F1 males expressed the yellow-body, white-eye traits. The
cross was carried to an F2 progeny, and only male offspring were tallied. On the basis of the data
shown here, a genetic map was constructed:
y
+
y
+
+
y
y
+
Phenotype
+
w
w
+
+
w
+
w
Male Offspring
8
7
88
97
444
356
0
0
ct
+
ct
+
ct
+
+
ct
a) Diagram the genotypes of the F1 parents
b) Assuming that white is at locus 1.5 on the X chromosome, construct a map
c) Were any double-crossover offspring expected?
1
Problem 3 (2 pts.): In tomato the genes for jointless (j), hairless (h), and leafy (lf) are known to
be linked on chromosome 5. Plants heterozygous for these three genes (j h lf) were testcrossed
and the progeny listed:
jointed
jointless
jointed
jointless
jointed
jointless
jointless
Phenotypes
hairless
hairy
hairy
hairless
hairy
hairless
hairy
normal
leafy
leafy
normal
normal
leafy
normal
Number
142
139
9
10
96
103
1
a) What is the correct sequence of genes in the linkage group?
b) What are the map distances between loci?
c) What is the coefficient of coincidence and the value of interference for this cross?
Problem 4 (2 pts.): In a cross in Neurospora involving two alleles B and b, the following tetrad
patterns were observed:
Tetrad Pattern
Number
BBbb
bbBB
BbBb
bBbb
BbbB
bBBb
45
55
5
5
2
8
Calculate the distance between the gene and the centromere.
Problem 5 (2 pts.): Rabbits fully heterozygous at three loci, BbCcSs (B=black, b=brown;
C=chinchilla, c=himalayan; S=long fur, s=short fur) are testcrossed and the 200 progeny are
tabulated.
Phenotype
Number
black
himalayan
long
35
brown
chinchilla
long
36
black
himalayan
short
35
brown
chinchilla
short
37
black
chinchilla
long
13
brown
himalayan
long
14
black
chinchilla
short
13
brown
himalayan
short
17
a) Which genes are linked? Which gene, if any, is not linked to the others?
b) Indicate the map distance between all linked genes.
2