Allele

Definition

An allele is one of two or more alternative forms of a gene that can occupy the same locus on a chromosome. Alleles contribute to the genetic diversity within a population by providing different versions of a particular trait or characteristic.

5 Must Know Facts For Your Next Test

1. Alleles can be either dominant or recessive, with dominant alleles masking the expression of recessive alleles.
2. The combination of alleles an individual inherits from their parents determines their genotype, which in turn influences their phenotype.
3. Genetic disorders can arise when an individual inherits two copies of a recessive allele, or one dominant and one recessive allele.
4. Genetic diversity within a population is increased by the presence of multiple alleles for a given gene, which can lead to a wider range of phenotypes.
5. Alleles can undergo mutations, leading to the creation of new allelic variants and further genetic diversity.

Review Questions

• Explain how alleles contribute to genetic diversity within a population.
  • Alleles contribute to genetic diversity by providing different versions of a particular gene or trait. When multiple alleles for a gene are present within a population, individuals can inherit different combinations of these alleles, resulting in a wider range of phenotypes and increased genetic variation. This diversity allows populations to adapt to changing environmental conditions and respond to selective pressures more effectively.
• Describe the relationship between genotype and phenotype, and how alleles influence this relationship.
  • An individual's genotype, which is the specific combination of alleles they inherit, directly influences their phenotype, or the observable physical and biochemical characteristics. Dominant alleles can mask the expression of recessive alleles, leading to the phenotypic expression of the dominant trait. Conversely, homozygous recessive individuals will express the recessive phenotype. The interaction between an individual's genotype and environmental factors ultimately determines their observable phenotype.
• Analyze the potential consequences of inheriting two copies of a recessive allele, and how this relates to genetic disorders.
  • When an individual inherits two copies of a recessive allele for a particular gene, they will express the recessive phenotype associated with that gene. This can lead to the development of genetic disorders, as the individual lacks the dominant, functional version of the gene. The inheritance of two recessive alleles is a common cause of many inherited genetic conditions, such as cystic fibrosis, sickle cell anemia, and phenylketonuria. Understanding the role of alleles in genetic disorders is crucial for identifying, diagnosing, and potentially treating these conditions.

Related terms

Genotype: The genetic makeup of an organism, consisting of the specific alleles present at each gene locus.

Phenotype: The observable physical or biochemical characteristics of an organism, which are the result of the interaction between its genotype and the environment.

Homozygous: A condition where an organism has two identical alleles for a particular gene, either both dominant or both recessive.