In Drosophila melanogaster the genes f, h and z are on the same chromosome. A
Drosophila triple mutant with the genotype ff hh zz is crossed with a trihybrid (an
individual who is heterozygous for all three genes) with the genotype f+f h+h z+z:
ff hh zz x f+f h+h z+z
The phenotypes expressed by the genotypes of these two parents are thus f h z and f+
h+ z+.
This cross produced a total of 1448 offspring with eight different phenotypes as below:
1) f h z:
592
+
+
+
2) f h z :
580
+
+
3) f h z:
45
4) f h z+:
40
+
5) f h z:
3
+
+
6) f h z :
5
7) f+ h z+:
89
+
8) f h z:
94
Total offspring:
1448
a- What is the name for this kind of cross?
b- What is the percentage of recombinants in this offspring generation?
c- What is the percentage of parental in this offspring generation?
d- What is the relative genetic distance (in cM) of the three genes on the
chromosome?
(1) between f and z:
(2) between f and h:
(3) between h and z:
Based on these results, which two genes are closest together on the chromosome?
(Draw a small map).