Final answer:
With independent assortment, half the progeny are recombinant and half are not, as genes segregate independently during the process of meiosis. The maximum predicted frequency of recombinant offspring in a test cross is 50%, which occurs when genes assort independently and are not linked.
Step-by-step explanation:
With independent assortment, half the progeny are recombinant and half the progeny are not. Independent assortment refers to Mendel's second law, where different genes independently separate from one another when reproductive cells develop through the process of meiosis.
For example, when Thomas Hunt Morgan and his colleagues performed test crosses with fruit flies for two traits, they observed a significant number of offspring showing recombination of traits that their parents didn't have. In their experiments, if genes were unlinked, they would see four types of gametes (AB, Ab, aB, ab) in equal frequencies.
However, when genes were linked, nonparental (recombinant) types such as Ab and aB occurred, but less frequently than parental types.
In one of Morgan's experiments, approximately 17% of the offspring showed recombination. Thus, the maximum percent possible in a test cross for two traits is 50%, representing complete independent assortment and no linkage.