A gene serves as a fundamental unit of heredity, acting as a set of instructions within our DNA that guides the development and functioning of an organism. These instructions dictate various characteristics, from how our bodies build proteins to our physical appearance. However, these genetic instructions are not always uniform; they can come in different “versions,” leading to the diversity observed among individuals.
Defining Gene Versions: Alleles
The scientific term for a version of a gene is an allele. Different alleles exist for the same gene, each located at the same specific position, or locus, on a chromosome. For instance, consider a gene that provides instructions for a particular characteristic, like eye color.
Similarly, the gene for eye color can have different alleles that lead to brown, blue, or green eyes. Each person inherits two copies of most genes, one from each biological parent. These two copies can be identical alleles, or they can be different versions. For example, the gene determining human ABO blood type has three common alleles: A, B, and O. The specific combination of these alleles determines an individual’s blood group.
How New Gene Versions Emerge
The existence of these different gene versions is not static; new alleles primarily arise through a process known as mutation. A mutation is a change in the DNA sequence of a gene. These changes can occur randomly, often as errors during DNA replication when cells divide. Environmental factors, such as exposure to radiation or certain chemicals, can also induce mutations.
Mutations are random events. While some can be harmful, many have no noticeable effect on an organism. Others can be beneficial, providing new variations that might help an organism adapt to its environment. This process continuously introduces new genetic variations into a population, serving as the raw material for diversity.
The Impact of Gene Versions on Traits
These gene versions have tangible effects on an organism’s characteristics, known as traits. The way different alleles interact determines which trait is expressed. A common interaction involves dominant and recessive alleles. A dominant allele will express its associated trait even if only one copy is present.
For example, the allele for brown eyes is dominant over the allele for blue eyes. If an individual inherits one allele for brown eyes and one for blue eyes, their eyes will be brown because the brown allele overrides the blue one. The blue eye trait only appears if a person inherits two copies of the recessive blue-eye allele, one from each parent.
Some traits, however, are more complex and are influenced by multiple alleles or even multiple genes working together. Eye color, for instance, is influenced by at least eight genes, not just one, which contributes to the wide spectrum of eye colors observed. This genetic variation underlies the individual differences seen within any species, influencing diverse characteristics like hair color, height, and even susceptibility to certain conditions.