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Question

Difficulty: HardGenetics and Heredity

In a certain animal population, an autosomal dominant trait appears in only 5% of individuals. Which statement correctly explains this observation?

  1. A
    Dominant alleles will inevitably increase over generations until they represent the majority of the population.
  2. B
    The trait must be controlled by a recessive allele because it occurs in less than half of the population.
  3. Dominance determines phenotypic expression in heterozygotes, not how common an allele is in a population.Answer
  4. D
    Dominant alleles automatically suppress and eliminate recessive alleles from the gene pool over time.

Answer

Dominance determines phenotypic expression in heterozygotes, not how common an allele is in a population.
Allele dominance describes how an allele manifests phenotypically in an individual organism (specifically, that a heterozygous genotype exhibits the dominant phenotype). It has no direct bearing on the allele's frequency or prevalence within the overall population gene pool, which is determined by evolutionary forces like natural selection, mutation rate, and genetic drift.

Step-by-Step Solution

1
Differentiate between genetic dominance and population allele frequency.
Dominance refers to the relationship between alleles at the individual/organismal level (a dominant allele masks a recessive allele in a heterozygote). Allele frequency refers to the proportion of a specific allele in the population's gene pool.
Clarifies the fundamental definition of dominance versus population prevalence.
2
Analyze why a dominant trait can remain rare within a population.
A dominant allele can exist at low frequency if it originally arose as a rare mutation or if it does not confer a selective survival or reproductive advantage.
Explains that population dynamics (natural selection, drift, mutation) govern frequency, not dominance.
3
Identify the statement that accurately reflects this biological distinction.
The statement explaining that dominance governs heterozygote expression rather than population abundance is correct.
Directly answers the stem question.

Key Concept

Distinction between allele dominance and allele frequency in population genetics
Estimated Time:1m 0s
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Topics

Genetics and Heredity

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