Question
- Describe how the genotypes RR and Rr result
in the same phenotype.
in the same phenotype.
Ask by Cross Best. in the United States
Jan 24,2025
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Tutor-Verified Answer
Answer
Both RR and Rr genotypes result in the same phenotype because the dominant allele ® masks the recessive allele ®, so both display the dominant trait.
Solution
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 ®: 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 ®: 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 ® and one recessive allele ®.
- 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 ® 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 ® is sufficient to express the dominant trait. The recessive allele ® 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.
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Simplify this solution Beyond the Answer
Both genotypes, RR and Rr, lead to the same phenotype because they both produce the dominant allele R. In genetics, the dominant allele ® can mask the expression of the recessive allele ®. Since RR has two copies of the dominant allele, while Rr has one dominant and one recessive allele, they both manifest the same observable traits, or phenotype. So, whether an organism is homozygous dominant (RR) or heterozygous (Rr), they’ll both display the characteristics associated with the dominant trait.
This principle mirrors the idea of a team wearing identical jerseys. If two players wear the same dominant color, like red, whether one player has a light version of that jersey or a dark version doesn’t change the fact that they both look like part of the same team! It’s all about appearance here.
