Question

Why do newly arisen beneficial recessive mutations take a long time to spread through natural populations? 


Answer 1

In a recessive inheritance, the phenotype caused by the mutant allele can only be expressed when an individual inherits two mutant recessive alleles, regardless of being beneficial or detrimental. This pattern follows the law of segregation. A typical recessive inheritance pattern yields offsprings that are 25% completely recessive expressing the phenotype, 25% that are normal and 50% that are carriers that do not express the phenotype. Hence, it will take a long time for the recessive mutation to spread through a natural population.