Question

In the pearl millet plant, color is determined by three alleles at a single locus: Rp²(red), Rp¹(purple), and rp (green). Red is dominant over purple and green, and purple is dominant over green (Rp²>Rp¹>rp). Give the expected phenotypes and ratios of offspring produced by the following crosses:

(a) Rp¹/Rp² × Rp¹/rp

      .

         (b) Rp¹/rp × Rp²/rp

         (c) Rp¹/Rp² × Rp¹/Rp²

     

         (d) Rp²/rp × rp/rp

         (e) rp/rp × Rp¹/Rp²

Answer 1

(a) Rp¹/Rp² × Rp¹/rp

expected phenotypes and ratios of offspring

¼ Rp¹/Rp¹(purple), ¼ Rp¹/rp (purple), ¼ Rp²/Rp¹(red), ¼ Rp²/rp (purple), for overall phenotypic ratio of ¾ purple, ¼ red.

         (b) Rp¹/rp × Rp²/rp

¼ Rp¹/Rp²(red), ¼ Rp¹/rp (purple), ¼ Rp²/rp (red), ¼ rp/rp (green), for overall phenotypic ratio of _^2/4 red, ¼ purple, ¼ green.

(c) Rp¹/Rp² × Rp¹/Rp²

      This cross is equivalent to a two-allele cross of heterozygotes, so the expected phenotypic ratio will be is ¾ red, ¼ purple.

         (d) Rp²/rp × rp/rp

      Another two-allele cross of a heterozygote with a homozygous recessive. Phenotypic ratio will be ½ purple, ½ green.

         (e) rp/rp × Rp¹/Rp²

               ½ Rp¹/rp (red), ½ Rp²/rp (purple)