Why Are the Progeny of a Testcross Generally Used to Map

Multiple Choice

Why are the progeny of a testcross generally used to map loci? Why not the F₂ progeny from an F₁ × F₁ cross?

A) Only recombinant offspring would be found in the progeny of an F₁ × F₁ cross.
B) The progeny of an F₁ × F₁ cross would be found in a 9:3:3:1 ratio when two genes are involved, whereas the progeny of a testcross would result in a 1:1:1:1 ratio.
C) It is easier to classify recombinant and parental offspring of a testcross than with the progeny of an F₁ × F₁ cross.
D) In a testcross more of the progeny would be expected to display the dominant phenotype than in the progeny of an F₁ × F₁ cross.
E) A testcross is more useful for mapping genes that are located near each other but, when genes are quite far apart on the same chromosome, an F₁ × F₁ cross actually is more useful.