key term - Recessive allele

Definition

A recessive allele is a variant of a gene that must be present in two copies, one from each parent, for its trait to be expressed in an organism. In the presence of a dominant allele, the recessive allele's effect is masked, meaning that the organism will display the dominant trait instead. Understanding recessive alleles is essential for grasping patterns of inheritance and how traits are passed down through generations.

5 Must Know Facts For Your Next Test

1. Recessive alleles can remain hidden in a population for generations, being carried by heterozygous individuals without expressing the trait.
2. For an offspring to express a recessive trait, both parents must contribute a recessive allele.
3. Some genetic disorders are caused by recessive alleles, such as cystic fibrosis and sickle cell anemia.
4. The presence of a recessive allele can affect phenotypic variation within a population, influencing traits like flower color in plants or blood type in humans.
5. Recessive alleles can be identified through breeding experiments, often using Punnett squares to predict offspring genotypes.

Review Questions

• How do recessive alleles interact with dominant alleles during inheritance?
  • Recessive alleles interact with dominant alleles by being masked when both types are present in an organism. If an organism has one dominant allele and one recessive allele for a trait, the dominant trait will be expressed, while the effect of the recessive allele will not be seen. Only when an organism inherits two recessive alleles, one from each parent, will the recessive trait become visible in its phenotype.
• Discuss how the concept of homozygosity and heterozygosity relates to the expression of recessive alleles.
  • Homozygosity and heterozygosity are key concepts in understanding how recessive alleles express themselves. An individual who is homozygous for a recessive allele will exhibit the associated trait because they have two copies of that allele. In contrast, a heterozygous individual carries one dominant and one recessive allele, which means the dominant trait will be expressed, effectively hiding the presence of the recessive allele. This genetic variation influences the overall phenotypic diversity within a population.
• Evaluate the role of recessive alleles in genetic disorders and how understanding these can aid in medical genetics.
  • Recessive alleles play a crucial role in many genetic disorders since these conditions often require two copies of a mutated gene for symptoms to manifest. Understanding this inheritance pattern allows medical genetics to identify carriers—individuals who have one normal and one mutated allele—who do not show symptoms but can pass the disorder onto their offspring. By analyzing family histories and employing genetic testing, healthcare providers can offer insights into risks for future generations, thus aiding in prevention and informed decision-making regarding reproductive options.

Related terms

dominant allele:

An allele that expresses its trait even when only one copy is present; it masks the effect of a recessive allele.

homozygous:

An organism is homozygous when it has two identical alleles for a specific gene, either dominant or recessive.

heterozygous:

An organism is heterozygous when it has two different alleles for a specific gene, one dominant and one recessive.