[Campbell Biology P.350] In Morgan's experiment Figure 15.9 , he performed a testcross with ... | Practice Question

In Morgan's experiment Figure 15.9 , he performed a testcross with an F1 dihybrid female b+b vg+vg . If the two genes for body color and wing size were NOT linked, what would be the expected phenotypic ratio in the offspring?

  • A: 1 wild type : 1 black-vestigial
  • B: 9 wild type : 3 black-normal : 3 gray-vestigial : 1 black-vestigial
  • C: 1 wild type : 1 black-vestigial : 1 gray-vestigial : 1 black-normal
  • D: 3 wild type : 1 black-vestigial

Explanation

If the genes were not linked, they would assort independently. The F1 female b+b vg+vg would produce four types of gametes b+vg+, bvg, b+vg, bvg+ in equal proportions 1:1:1:1 . A testcross with a homozygous recessive male bvg would then yield offspring with four different phenotypes in a 1:1:1:1 ratio, corresponding to the four types of eggs.