Diploid 2n6

1
Using trisomics to locate genes on specific
chromosomes
Diploid 2n6
1 2 3
On which chromosome is locus a? Wild type
a Mutant a
2
In which chromosome is locus a?
Test Cross all trisomics to aa and look for
deviant ratios
3
Trisomic ratio
Phenotypic ratio 5 a 1a
Therefore locus a is on chromosome 2
4

Disomic ratios tells us that a is not on
chromosomes 1 or 3
Diploid mutant
Triplo-1
a a
a a
Test cross 1 aa 1aa
F1
a a
Conclusion a is not on chromosome 1 We will
reach same conclusion in crosses involving mutant
aa and triplo-3