Recessive allele

Definition

A recessive allele is a variant of a gene that must be present in two copies (homozygous) for its associated trait to be expressed. In the presence of a dominant allele, the effect of the recessive allele is masked, meaning that traits linked to it won't show unless an individual has two copies of the recessive allele. This concept is foundational in understanding how traits are inherited through generations and is key in the study of inheritance patterns.

5 Must Know Facts For Your Next Test

1. Recessive alleles can remain hidden in a population if they are carried by individuals with a dominant allele, making them less likely to be expressed in observable traits.
2. An individual must inherit one recessive allele from each parent to display the trait associated with that allele.
3. Recessive alleles are often represented by lowercase letters in genetic notation, while dominant alleles are represented by uppercase letters.
4. Certain genetic disorders and conditions can be caused by recessive alleles, such as cystic fibrosis or sickle cell anemia, where an individual must have two copies of the recessive allele to show symptoms.
5. In Punnett squares used for predicting offspring genotypes, recessive alleles contribute to the ratio of potential phenotypes among offspring based on parental genotypes.

Review Questions

• How does the interaction between dominant and recessive alleles determine an organism's phenotype?
  • The interaction between dominant and recessive alleles plays a crucial role in determining an organism's phenotype. A dominant allele will express its trait even if only one copy is present, while a recessive allele only expresses its trait when two copies are present. This means that an organism with one dominant and one recessive allele will display the phenotype associated with the dominant allele. Understanding this relationship helps explain why certain traits may appear more frequently in a population.
• Discuss how recessive alleles can lead to genetic disorders and give examples of such disorders.
  • Recessive alleles can lead to genetic disorders when an individual inherits two copies of the allele associated with the disorder. For instance, cystic fibrosis results from a mutation in the CFTR gene, which is recessive. An individual must inherit one defective CFTR gene from each parent to develop cystic fibrosis symptoms. Similarly, sickle cell anemia is caused by a recessive allele affecting hemoglobin production. These examples illustrate how recessive alleles can have significant impacts on health when expressed.
• Evaluate the importance of understanding recessive alleles in genetic counseling and breeding programs.
  • Understanding recessive alleles is crucial in genetic counseling and breeding programs because it helps predict the likelihood of offspring inheriting certain traits or disorders. Genetic counselors utilize knowledge about recessive inheritance patterns to inform prospective parents about risks related to genetic conditions that may run in their families. In breeding programs, whether for plants or animals, recognizing how recessive traits can express themselves allows breeders to make informed decisions to enhance desired traits while managing health issues related to recessive genetic disorders.

Related terms

dominant allele: A dominant allele is a variant of a gene that expresses its trait even when only one copy is present in an individual, overshadowing the effect of a recessive allele.

homozygous: An individual is homozygous for a gene if they carry two identical alleles, whether dominant or recessive, leading to consistent expression of a specific trait.

phenotype: Phenotype refers to the observable traits or characteristics of an organism that result from the interaction between its genotype and the environment.