Which of the following represents the phenotypic ratio, when a plant Rr is crossed with another plant Rr, assuming that the gene R for round seed is dominan...

Which of the following represents the phenotypic ratio, when a plant Rr is crossed with another plant Rr,
assuming that the gene R for round seed is dominant and wrinkled r is recessive?

Answer Details

The cross between a plant with genotype Rr (where R is the dominant allele for round seed and r is the recessive allele for wrinkled seed) and another Rr plant can be represented as follows: | | R | r | | - | - | - | | R | RR | Rr | | r | Rr | rr | The Punnett square above shows that the offspring can have the genotypes RR, Rr, or rr in a ratio of 1:2:1 respectively. Since the round seed trait is dominant, the plants with genotypes RR and Rr will have a round seed phenotype. Only the plants with genotype rr will have the wrinkled seed phenotype. Therefore, the phenotypic ratio of the offspring is 3:1 (round seed : wrinkled seed) as only one out of four possible outcomes has the recessive trait (wrinkled seed). Thus, option (D) represents the correct phenotypic ratio for this cross.