In the dihybrid cross AaBb x aabb, what proportion of the F1 offspring will be t
ID: 81960 • Letter: I
Question
In the dihybrid cross AaBb x aabb, what proportion of the F1 offspring will be true breeding?
I created this punnett square and to me it looks as if 1/4 of the offspring would be AaBb, and another 1/4 would be aabb. Which in my mind means half F1 would be true breeding (1/4+1/4)....but this answer was marked wrong on the test. What am I doing wrong? And is this a trick question, can you not have true breeding if you have two parents that do not have the same homozygous genotype?
AB Ab aB ab ab AaBb Aabb aaBb aabb ab AaBb Aabb aaBb aabb ab AaBb Aabb aaBb aabb ab AaBb Aabb aaBb aabbExplanation / Answer
Answer:
A true-breeding plant is one that, when self-fertilized, only produces offspring with the same traits. True-breeding plants and organisms may express phenotypes that are either homozygous dominant or homozygous recessive.
In the above cross, true breedings are those with aabb genotype. So, proportion of F1 offspring that will be true breeding = 4/16 = 1/4 (25%)