Alleles

Definition

Alleles are the different versions of a gene that can occupy the same location on a chromosome. They determine the specific traits or characteristics an organism will express.

5 Must Know Facts For Your Next Test

1. Alleles can be either dominant or recessive, influencing the expression of a particular trait.
2. An organism's genotype is the combination of alleles it possesses for a given gene, while the phenotype is the observable trait expressed.
3. Genetic variation within a population is created by the presence of multiple alleles for the same gene.
4. Alleles are the basis for inheritance, as they are passed from parents to offspring during reproduction.
5. Mutations in genes can lead to the creation of new alleles, contributing to the diversity of traits within a species.

Review Questions

• Explain how alleles contribute to genetic variation within a population.
  • Alleles are the different versions of a gene that can occupy the same location on a chromosome. The presence of multiple alleles for the same gene within a population creates genetic variation, as individuals can inherit different combinations of alleles. This diversity of alleles leads to a range of possible phenotypes, or observable traits, that can be expressed within the population. The existence of allelic variation is a fundamental mechanism driving evolution, as it provides the raw material for natural selection to act upon.
• Describe the relationship between genotype and phenotype, and how alleles influence this relationship.
  • An organism's genotype is the specific combination of alleles it possesses for a given gene, while the phenotype is the observable physical or biochemical characteristic that is expressed. Alleles can be either dominant or recessive, and the way they interact determines the phenotype that is ultimately expressed. Dominant alleles are always expressed in the phenotype, even if only one copy is present. Recessive alleles are only expressed when two copies are present, as the dominant allele will mask the recessive one. This interplay between genotype and phenotype, mediated by alleles, is a crucial concept in understanding how genetic information is translated into an organism's observable traits.
• Analyze how mutations in genes can lead to the creation of new alleles and contribute to the evolution of a species.
  • Mutations are changes in the DNA sequence of a gene, and these mutations can result in the creation of new alleles. When a mutation occurs, it can introduce a different version of the gene, which then becomes an alternative allele. The presence of these new alleles within a population increases the overall genetic diversity, as individuals can inherit different combinations of alleles. This diversification of alleles is a fundamental driver of evolution, as it provides the raw material for natural selection to act upon. Organisms with beneficial alleles are more likely to survive and reproduce, passing on their advantageous traits to future generations. Over time, the accumulation of genetic changes through the creation of new alleles can lead to the evolution of new species and the adaptation of existing ones to changing environmental conditions.

Related terms

Genotype: The genetic makeup of an organism, including the specific alleles it possesses for each gene.

Phenotype: The observable physical and biochemical characteristics of an organism, which are determined by its genotype and environmental factors.

Dominant and Recessive Alleles: Dominant alleles are expressed in the phenotype when present, while recessive alleles are only expressed when two copies are present.