[Campbell Biology P.350] In Morgan's actual experiment, the majority of the testcross offspr... | Practice Question

In Morgan's actual experiment, the majority of the testcross offspring had parental phenotypes wild type or black-vestigial . What did this result indicate?

  • A: The genes for body color and wing size are on different chromosomes.
  • B: The genes for body color and wing size are genetically linked on the same chromosome.
  • C: The wild-type alleles (b+ and vg+) are dominant over the mutant alleles.
  • D: A mistake was made in the experiment, and the results are invalid.

Explanation

The fact that the number of offspring with parental phenotypes 965 wild type, 944 black-vestigial was far higher than the number with nonparental, recombinant phenotypes 206 gray-vestigial, 185 black-normal strongly indicated that the genes were inherited together. This deviation from the 1:1:1:1 ratio expected for independent assortment is the classic evidence for genetic linkage.