BIOL 304 Practice problem: 3-Point Test Cross
Problem 7-16 from the handout passed out in class is as follows:
Given the following testcross data for corn in which the genes for fine stripe (f), bronze
aleurone (bz) and knotted leaf (Kn) are involved:
Phenotype
Kn + +
Kn f +
+++
+ f bz
Kn + bz
+ + bz
+f+
Kn f bz
Total:
Number
451
134
97
436
18
119
24
86
1,365
Maize geneticists tend to be like Drosophila geneticists utilizing a + to indicate the wild
type allele (which also is dominant) and a lower case letter for the mutant allele (which is
recessive). The first thing I suggest in attacking this problem is to use the typical
convention of upper case letters for dominant alleles and lower case letters for recessive
alleles as follows:
F = wild type, f = fine stripe;
B = wild type, b = bronze aleurone
K = wild type, k = knotted leaf
Then we can rewrite the phenotypes in a “language” that is more easily understood:
Phenotype
kFB
k f B
KFB
Kf b
k F b
KFb
KfB
k f b
Total:
Number
451
134
97
436
18
119
24
86
1,365
a) Determine the sequence (order) of the three genes.
b) Calculate the amount of recombination that occurred between each pair of genes.