Two genes in chromosome 7 of corn are identified by the recessive alleles g (for glossy leaves) and r (for branching of ears). When a plant heterozygous for each of these alleles was crossed to a double recessive plant, the progeny consisted of the following genotypes, with the numbers of each indicated Gr/gr 80 GR/gr 8 Gr/gr 10 gR/gr 77 What is the genotype of the double heterozygous parent?

GgRr

Explanation:

as it was stated in the question that one of the parent is a heterozygote for both alleles, It could only be written as GgRr.  A cross between this parent and the double recessive parent would also give rise to the following listed genotypes, assuming the second Gr/gr in the question to be gr/gr. thus, we would have:

GgRr   x     ggrr

         GR         Gr       gR       gr

gr      GR/gr  Gr/gr    gR/gr   gr/gr

the median of the data is 4.5.