HELLL Bright purple true breeding plums(P) was bred with white true breeding plums
(p). The F1 generation were light lilac. One F1 individual for the above was then
used in a testcross. What proportion of the progeny will be white?

The correct answer is - 50% or 1/2.

Explanation:

In the given case it is given that the true-breeding purple (P) plum bred with true-breeding white (p) plum and result in light lilac offsprings which suggests that there is incomplete dominance between these genes.

By the cross of these parent generation, there would be all heterozygous offspring that then used in testcross which is the cross between the dominant phenotype to the recessive plant so,

Gametes: P, p and p, p

      P      p

p     Pp    pp

p    Pp     pp

So the half or 1/2 proportion of the total offsprings would be white plums.