- Describe how the genotypes RR and Rr result in the same phenotype.

In genetics, the relationship between genotypes and phenotypes is often determined by the dominance of alleles. When considering the genotypes **RR** and **Rr**, both result in the same phenotype due to the principles of **dominant-recessive allele interaction**. Here's a detailed explanation: ### **1. Understanding Alleles and Genotypes** - **Alleles** are different versions of a gene that reside at the same position (locus) on homologous chromosomes. - **Genotypes** refer to the combination of alleles an organism possesses for a particular trait. - **RR**: Homozygous dominant genotype (two dominant alleles). - **Rr**: Heterozygous genotype (one dominant allele and one recessive allele). ### **2. Dominant and Recessive Alleles** - **Dominant Allele (R)**: An allele that masks the expression of a recessive allele when both are present in a genotype. It determines the phenotypic trait when at least one copy is present. - **Recessive Allele (r)**: An allele that is masked by the dominant allele in a heterozygous pairing. It only determines the phenotype when two copies are present (rr). ### **3. Phenotypic Expression** - **RR Genotype**: - Both alleles are dominant. - The dominant trait is expressed because there are no recessive alleles to mask it. - **Phenotype**: Displays the dominant trait. - **Rr Genotype**: - One dominant allele (R) and one recessive allele (r). - The dominant allele masks the presence of the recessive allele. - **Phenotype**: Also displays the dominant trait, identical to the RR genotype. ### **4. Example Scenario** Consider the trait for flower color in pea plants, where: - **R** = Red flower color (dominant) - **r** = White flower color (recessive) - **RR** plants will have red flowers. - **Rr** plants will also have red flowers because the dominant R allele masks the recessive r allele. - Only **rr** plants will have white flowers. ### **5. Implications in Genetics** - **Phenotypic Dominance**: The presence of at least one dominant allele (R) ensures that the dominant phenotype is expressed, regardless of whether the second allele is dominant or recessive. - **Genotypic Diversity**: While RR and Rr have the same phenotype, their genotypes are different, contributing to genetic diversity within a population. ### **6. Summary** Both **RR** (homozygous dominant) and **Rr** (heterozygous) genotypes result in the same phenotype because the dominant allele (R) is sufficient to express the dominant trait. The recessive allele (r) in the Rr genotype does not influence the phenotype due to its masked presence by the dominant R allele. --- **Visual Representation:** | Genotype | Allele Combination | Phenotype | |----------|---------------------|--------------------| | RR | R + R | Dominant trait (e.g., Red flowers) | | Rr | R + r | Dominant trait (e.g., Red flowers) | | rr | r + r | Recessive trait (e.g., White flowers) | This table illustrates that both RR and Rr genotypes lead to the dominant phenotype, while only rr leads to the recessive phenotype.