Practice question

Question

A Drosophila mutant (line A) with vestigial wings is isolated in a laboratory. The vestigial wing phenotype was observed to be recessive and mapped to gene ‘X’. Three other laboratories also isolated vestigial mutants, called line B, C and D. In order to test if the mutation in lines B-D also mapped to gene ‘X’, the following crosses were made and phenotype of F1 progeny observed. Based on the above identify the line(s) which is most likely NOT to have a mutation in gene ‘X’.