Genes contain the instructions that determine an organism’s traits. Different versions of a gene are known as alleles, and these variations contribute to the diversity seen among individuals. Dominant alleles represent a specific type of allele that can express its associated trait even when only one copy is present in an individual’s genetic makeup. This means that the characteristic linked to a dominant allele will be observable if an individual inherits it from either parent.
How Dominant Alleles Determine Traits
Each person inherits two copies of most genes, with one copy coming from each biological parent. These two alleles together form an individual’s genotype for a particular trait, while the observable characteristic, such as eye color, is called the phenotype. When a dominant allele is part of this pair, its trait will be expressed in the phenotype, regardless of the other allele present. This occurs because the dominant allele effectively “masks” or overrides the presence of a recessive allele if both are inherited.
For instance, if an individual inherits an allele for brown eyes, which is dominant, and an allele for blue eyes, which is recessive, their eyes will be brown. The genetic information carried by the dominant allele is sufficient to produce the specific protein or regulatory effect that results in the observed characteristic, ensuring even a single dominant allele can dictate the outward appearance of a trait.
Common Examples of Dominant Traits
Many human characteristics are influenced by dominant alleles. Brown eye color, for example, is a common dominant trait over blue eye color, meaning individuals with at least one brown eye allele typically have brown eyes. Another widely recognized dominant trait is the ability to roll one’s tongue into a U-shape. This ability is present if an individual inherits just one dominant allele for tongue rolling.
Having free earlobes, where the lobe hangs unattached from the head, is also a dominant trait, while attached earlobes are associated with a recessive allele. The presence of dimples on the cheeks serves as another example of a dominant trait. Even traits like a widow’s peak hairline, which forms a V-shape in the middle of the forehead, are determined by a dominant allele.
Dominant vs. Recessive Alleles
Alleles vary in their expression, and their interaction determines how traits are manifested. Recessive alleles, by contrast, only express their associated trait when two copies are present, one inherited from each parent. If an individual inherits one dominant and one recessive allele, the dominant allele will prevent the recessive trait from appearing. For a recessive trait to be observed, an individual must inherit two copies of the recessive allele, ensuring no dominant allele is present to mask it. This distinction clarifies how dominant alleles can “hide” the presence of recessive ones in the phenotype.