Organisms inherit a variety of features from their parents, and these features, known as traits, can manifest in predictable patterns. Some traits appear more readily than others, even if the genetic information for a different version of that trait is also present. This difference in appearance highlights a key principle of inheritance, where certain genetic instructions take precedence over others in determining an observable characteristic.
Defining Dominant Traits
A dominant trait is an observable characteristic that appears in an individual even if only one copy of the genetic instruction for that trait is inherited. This means that if an individual receives a genetic instruction for a dominant trait from one parent and a different instruction for the same trait from the other parent, the dominant version will be the one expressed. The genetic instruction that is masked or overridden by a dominant trait is known as a recessive trait. A recessive trait will only become apparent if an individual inherits two copies of its specific genetic instruction, one from each parent.
How Dominant Traits Are Expressed
The expression of dominant traits is rooted in the interaction of alleles, which are different versions of a gene. Every individual inherits two alleles for each gene, one from each parent. When at least one of these alleles is a dominant allele, it will determine the observable characteristic, or phenotype, of the individual. For instance, if a dominant allele is paired with a recessive allele, the dominant allele’s instruction will be followed, masking the effect of the recessive one.
The genetic makeup of an individual, including both expressed and unexpressed alleles, is called the genotype. The phenotype, in contrast, refers to the physical and observable characteristics that result from that genotype. In the context of dominant traits, a person can have a genotype with two dominant alleles or one dominant and one recessive allele, yet both genotypes will result in the same dominant phenotype. This occurs because the single dominant allele provides enough information for the trait to be fully expressed.
Common Examples of Dominant Traits
Many common human characteristics are determined by dominant traits. For example, having detached earlobes is a dominant trait, while attached earlobes are recessive. The ability to roll one’s tongue into a U-shape is also a dominant trait, with the inability to do so being recessive.
Another easily recognized dominant characteristic is a widow’s peak, which is a V-shaped hairline at the center of the forehead. A straight hairline is the recessive counterpart. While eye color is complex and influenced by multiple genes, brown eyes are generally considered dominant over blue eyes.