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Difficulty: MediumBasic Genetics Terminology and Concepts

During a crop breeding experiment, two individual maize plants both exhibit resistance to a fungal pathogen. Genetic sequencing reveals that Plant 1 has the genetic constitution RRRR, whereas Plant 2 has the genetic constitution RrRr. Which of the following statements correctly compares the genetic characteristics of these two plants?

  1. They express the same phenotype but possess different genotypes.Answer
  2. B
    They possess the same genotype but express different phenotypes.
  3. C
    Plant 1 is heterozygous dominant, whereas Plant 2 is homozygous recessive.
  4. D
    They share identical genotypes because environmental factors mask the recessive allele.

Answer

They express the same phenotype but possess different genotypes.
Phenotype refers to the observable physical characteristics of an organism, while genotype refers to its specific genetic composition. Because allele RR is dominant over allele rr, both RRRR and RrRr produce the disease-resistant phenotype. However, their genotypes differ because one plant is homozygous dominant (RRRR) while the other is heterozygous (RrRr).

Step-by-Step Solution

1
Identify the phenotypic expression of both plants.
Both Plant 1 (RRRR) and Plant 2 (RrRr) exhibit resistance to the fungal pathogen, meaning they have identical phenotypes.
Phenotype is the observable physical or physiological trait of an organism produced by the interaction of its genotype with the environment.
2
Analyze the genotypic constitution of each plant.
Plant 1 is homozygous dominant (RRRR) and Plant 2 is heterozygous (RrRr).
Genotype refers to the actual allele combination present at a specific gene locus.
3
Compare the phenotype and genotype between the two plants.
The two plants share the same observable phenotype (disease resistance) despite having different genotypes (RRRR versus RrRr).
The dominant allele (RR) completely masks the presence of the recessive allele (rr) in the heterozygous state.

Key Concept

Phenotype vs. Genotype and Allelic Dominance
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Topics

Basic Genetics Terminology and Concepts

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