Mendels Yy Rr dihybrid pea plants were the F1 of the cross b

Mendel’s Y/y; R/r dihybrid pea plants were the F1 of the cross between a double homozygous dominant and a double homozygous recessive. If we testcrossed these dihybrids, what proportion of the offspring would be recombinant and phenotypically resemble the F1 dihybrid?

The correct znswer is 0% but I\'m confused on why that is. Can someone explain this?

Solution

Answer:

Y/y; R/r x y/y; r/r----------Test cross

Y/y; R/r plant produces four types of gametes, YR, Yr, yR & yr

Yr and yR gametes are recombinant gametes.

y/y; r/r plant produces only one type of gametes, yr.

If you cross Yr and yR (recombinant) gametes with yr, no progeny will be phenotypically Y/y; R/r.

If recombination doesn\'t occur in the genes in F1 hybrid, then phenotypically Y/y; R/r hybrid will be produced