Selection will not eliminate a lethal recessive gene from a large population because

Options

A. there are always some heterozygote carriers of the allele
B. gene fixation occurs in population
C. heterozygotes are at a selective advantage
D. rate of mutation to the lethal allele is high

Answer

**Step-by-Step Solution:**

1. **Understanding Lethal Recessive Genes**: A lethal recessive gene is an allele that can cause death when an individual has two copies of it (homozygous recessive). If an individual has one copy of the dominant allele (heterozygous), they do not express the lethal trait.

2. **Genotypes Involved**: In a population, individuals can have three genotypes regarding a lethal recessive gene:
- Homozygous dominant (AA) - normal phenotype
- Heterozygous (Aa) - carrier, normal phenotype
- Homozygous recessive (aa) - exhibits the lethal trait and does not survive.

3. **Role of Heterozygote Carriers**: Heterozygote carriers (Aa) do not show the lethal phenotype but can pass the recessive allele (a) to their offspring. This means that even if the homozygous recessive individuals (aa) do not survive, the allele continues to exist in the population through the heterozygotes.

4. **Selection Pressure**: Natural selection may eliminate homozygous recessive individuals (aa) from the population, but it cannot eliminate the allele itself because the heterozygotes (Aa) remain unaffected and continue to reproduce.

5. **Conclusion**: Therefore, the presence of heterozygote carriers ensures that the lethal recessive gene persists in the population despite the selection pressure against the homozygous recessive individuals. This is why selection will not eliminate a lethal recessive gene from a large population.

**Final Answer**: The correct answer is option A: There are always some heterozygote carriers of the allele.

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