In fruit flies, red eyes color (r) is dominated to brown (r), and normal spine (s) is dominated to spineless (s). many flies are produced with maintaining two heterozgous parents.
what fractions of the offspring will be red eyed, and have normal spines?

The percentage of progenies with red eyes and spine will be 56.25%.

This cross will be just similar to Mendel’s Dihybrid cross where he crossed the pea plants considering two characters at once.

Here two characters that are taken into account are eye colour and presence of spine. The eye colour has two traits - red and brown. Red colour is dominant. The presence of spine has also two possibilities - presence of spine or absence of spine.

The allele denoting red eye colour is R and allele denoting brown eye colour is r. Similarly, the allele denoting presence of spine is S and absence of spine is s.

Genotype of the heterozygous parents = RrSs.

Gametes produced by the parents= RS, Rs, rS and rs.

So crossing them, we get the phenotypic ratio of red eyed spined : red eyed spineless : brown eyed spined : brown eyed spineless = 9:3:3:1.

So, the percentage of red eyed spined = 56.25%.

the correct option is option a