44. Under which condition of natural selection no allele would be lost when
    (1) Any one homozygote is favored
    (2) Both homozygote are favored
    (3) Heterozygote are favored
    (4) Heterozygote is not favored

Correct answer:
(3) Heterozygote are favored

Introduction

Genetic diversity is essential for the adaptability and survival of populations. One of the most important evolutionary mechanisms for maintaining this diversity is the heterozygote advantage. This form of natural selection ensures that no allele is lost from the gene pool, even if one allele might be harmful in a homozygous state.

What Is Heterozygote Advantage?

Heterozygote advantage occurs when individuals with two different alleles for a gene (heterozygotes) have a higher fitness than individuals with two identical alleles (homozygotes). This advantage leads to balancing selection, which maintains both alleles in the population over time.

How Does It Work?

• Maintains Polymorphism: When heterozygotes are favored, both alleles are preserved, and neither is lost through selection.

• Stable Equilibrium: The population reaches a genetic equilibrium where both alleles remain at stable frequencies.

• Classic Example: The sickle cell trait in humans, where heterozygotes are resistant to malaria and do not suffer from sickle cell disease, is a textbook case.

Evolutionary Significance

• Preserves Genetic Variation: This mechanism is vital for the long-term adaptability of populations, allowing them to respond to changing environments.

• Prevents Allele Loss: Unlike other forms of selection, heterozygote advantage ensures that both alleles are maintained, preventing the fixation or loss of any single allele.

Conclusion

When heterozygotes are favored by natural selection, both alleles are maintained in the population, and no allele is lost. This form of balancing selection is crucial for preserving genetic diversity and promoting evolutionary resilience.

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Heterozygote advantage illustrates how evolution can maintain diversity, ensuring populations are equipped to survive in a changing world.