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Difficulty: MediumGenetics and Heredity

In Mendelian genetics, what characteristic definitively identifies an allele as dominant?

  1. A
    It is the most frequently occurring allele within a natural population.
  2. It is expressed in the phenotype whenever at least one copy is present in the genotype.Answer
  3. C
    It requires two identical copies in the genotype to produce an observable physical trait.
  4. D
    It permanently eliminates the paired recessive allele during gamete formation.

Answer

An allele is dominant if it is expressed in the phenotype whenever at least one copy is present in the genotype.
In genetics, a dominant allele is defined by its ability to determine the organism's physical phenotype even when only a single copy is inherited alongside a recessive allele. Therefore, an individual with either a heterozygous genotype or a homozygous dominant genotype will express the dominant trait.

Step-by-Step Solution

1
Define genetic dominance at the individual level
Dominance refers to the interaction between alleles of a gene in an individual, where the presence of a dominant allele masks the expression of a recessive allele.
Dominance is a biochemical expression property within a genotype, not a measure of population frequency or evolutionary fitness.
2
Determine the genotypic conditions required for expression
An organism with either a homozygous dominant genotype or a heterozygous genotype will display the dominant phenotype.
Only one copy of a dominant allele is necessary for the corresponding trait to be physically observed.
3
Distinguish dominance from population frequency and segregation laws
Dominant traits are not necessarily the most common in a population, nor do they destroy recessive alleles.
Alleles maintain their structural integrity and separate cleanly into gametes during meiosis regardless of dominance relationships.

Key Concept

Dominant alleles mask recessive alleles in heterozygous genotypes and are expressed whenever at least one copy is present.
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Topics

Genetics and Heredity

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