Recessive allele

Definition

A recessive allele is a version of a gene that must be present in two copies (homozygous) for it to manifest in an organism's phenotype. This means that if an individual carries one dominant allele and one recessive allele, the dominant trait will be expressed, while the recessive trait will remain hidden. Understanding recessive alleles is crucial for predicting inheritance patterns and genetic variation within populations.

5 Must Know Facts For Your Next Test

1. Recessive alleles can skip generations, showing up in offspring only if both parents pass on the recessive variant.
2. In a Punnett square, a recessive allele is typically represented by a lowercase letter, while the dominant allele is represented by an uppercase letter.
3. The expression of a recessive trait can occur in organisms that are homozygous recessive (having two copies of the recessive allele).
4. Certain traits governed by recessive alleles can lead to genetic disorders when individuals inherit two copies of the harmful allele.
5. The frequency of recessive alleles in a population can be tracked using methods like the Hardy-Weinberg equilibrium, which helps predict genetic variation over time.

Review Questions

• How do recessive alleles influence phenotypic expression in offspring when considering parental genotypes?
  • Recessive alleles only influence phenotypic expression when an individual inherits two copies of the recessive variant from its parents. If one parent contributes a dominant allele and the other a recessive allele, the dominant trait will be expressed in the offspring. This pattern highlights how the combination of alleles from both parents determines the visible characteristics of their offspring.
• Discuss the implications of recessive alleles on genetic disorders and how they can be inherited within families.
  • Recessive alleles are significant in the context of genetic disorders, as many conditions arise when an individual inherits two copies of a harmful recessive allele. For example, cystic fibrosis and sickle cell anemia are caused by recessive alleles. If both parents are carriers (heterozygous), there is a 25% chance with each pregnancy that their child will be affected by the disorder, demonstrating how these alleles can persist in a population despite being linked to disease.
• Evaluate how understanding recessive alleles and their inheritance patterns contributes to population genetics and the study of genetic diversity.
  • Understanding recessive alleles is crucial for population genetics as it helps explain genetic variation within populations. By applying models like the Hardy-Weinberg equilibrium, scientists can predict how allele frequencies change over time due to factors like selection, mutation, and migration. Recessive alleles may remain hidden in heterozygous carriers, but their presence can affect overall genetic diversity and evolutionary potential, influencing how populations adapt to changing environments.

Related terms

dominant allele: A dominant allele is a variant of a gene that can mask the presence of a recessive allele in determining the organism's phenotype, requiring only one copy to be expressed.

homozygous: Homozygous refers to having two identical alleles for a particular gene, either both dominant or both recessive.

heterozygous: Heterozygous means having two different alleles for a particular gene, where one may be dominant and the other recessive.