Allele

Definition

An allele is a variant form of a gene that arises by mutation and is found at the same place on a chromosome. Different alleles can result in variations in traits or characteristics among individuals, such as flower color or blood type. The presence of multiple alleles for a single gene can lead to diversity within a population, impacting how traits are expressed and inherited.

5 Must Know Facts For Your Next Test

1. Alleles can be dominant or recessive, influencing the phenotype based on their interactions in an organism's genotype.
2. The combination of alleles an individual has for a specific gene is known as their genotype, which ultimately determines their phenotype.
3. Alleles can arise from mutations in the DNA sequence, creating new variations that can be passed on to future generations.
4. In diploid organisms, such as humans, alleles are present in pairs—one inherited from each parent—which contributes to genetic diversity.
5. The concept of multiple alleles exists when more than two variants of a gene exist within a population, exemplified by the ABO blood group system.

Review Questions

• How do different alleles contribute to genetic variation within a population?
  • Different alleles introduce variability in traits among individuals by providing alternative versions of genes. This variation occurs because alleles may code for different proteins or influence the amount of protein produced, leading to diverse physical traits or behaviors. The presence of multiple alleles within a population enhances genetic diversity, which is essential for evolution and adaptation.
• Discuss the implications of homozygous and heterozygous genotypes on phenotypic expression.
  • Homozygous genotypes consist of two identical alleles, which typically result in consistent trait expression, while heterozygous genotypes involve two different alleles that may interact differently. In cases where one allele is dominant, the phenotype will reflect that dominant trait. Conversely, when both alleles contribute to the phenotype, it may result in intermediate or blended traits. This distinction is crucial for predicting how traits will be expressed in offspring.
• Evaluate how the concept of multiple alleles expands our understanding of inheritance patterns in genetics.
  • The concept of multiple alleles challenges the traditional Mendelian view of inheritance by showing that more than two allele forms can exist for a single gene within a population. This understanding allows for more complex inheritance patterns, such as codominance and incomplete dominance. For instance, the ABO blood group system illustrates how multiple alleles determine blood type and how these variations can impact blood transfusions and disease susceptibility, emphasizing the importance of genetic diversity.

Related terms

gene: A gene is a segment of DNA that contains the instructions for building proteins and can influence traits in an organism.

homozygous: An individual is homozygous for a particular gene when they have two identical alleles for that gene, which can affect trait expression.

heterozygous: An individual is heterozygous for a gene when they have two different alleles, leading to potential variation in the expression of traits.