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Difficulty: EasyBasic Genetics Terminology and Concepts

An allele whose phenotype is expressed in an organism only when two copies of it are present, and whose effect is masked in the presence of a contrasting allele, is best described as which of the following?

  1. A recessive alleleAnswer
  2. B
    A dominant allele
  3. C
    A codominant allele
  4. D
    A continuous allele

Answer

A recessive allele
The correct option is 'A recessive allele' because recessive traits require two identical recessive alleles (homozygous state) to be observed phenotypically. In a heterozygous individual, the dominant allele overrides and masks the recessive trait.

Step-by-Step Solution

1
Analyze the definition given in the stem.
The stem describes an allele that requires two copies (homozygous condition) to manifest phenotypically and is masked when paired with a different allele.
By definition in classical Mendelian genetics, an allele that is concealed in the heterozygous condition is recessive.
2
Evaluate the choices against basic genetics terminology.
A recessive allele fits this exact criterion, whereas a dominant allele masks others and a codominant allele expresses alongside others.
Distinguishing between dominant, recessive, and codominant expression is fundamental to genetic analysis.

Key Concept

Recessive Allele Expression
Estimated Time:45s
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Topics

Basic Genetics Terminology and Concepts

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