Question

a plant has three linked genes , ABC , however the gene order is unknown . the following cross is performed .Abc/Abc*aBC/aBC.The F1 individuals are crosses to a tester plant. you count 100 progeny and you notice that you only find one ABC/abc plant and no abc/abc plants. you find six other classes of genotypes , all of which ahve at least 10 plants in each class. which is the order of genotype?

Answer 1

Parental cross Abc/Abc x aBC/aBC

Gametes Abc (From Abc/Abc) & aBC (From aBC/aBC)

F1 All Abc/aBC

Now, F1 individuals are crossed with tester plant (Genotype abc/abc). So, gametes from tester plant will be abc. Now, cross with tester plant will produce least double cross-over progeny in the F2. As, ABC/abc produced only 1 time & no abc/abc plant is produced, these two are double cross-over progeny. Only possible way that these two can be double cross-over progeny is if the gene order is BAC.

Thus, correct gene order will be BAC.