The differences observed between individuals within a species, from physical appearance to internal biochemistry, are collectively known as variation. This biological phenomenon is fundamental to life and provides the raw material necessary for evolutionary change over time. Inherited variation specifically refers to the differences in characteristics that are passed down genetically from parents to their offspring. This mechanism explains why children share many traits with their parents but are never exact duplicates.
Understanding Inherited Variation
Inherited variation is defined by the differences in the sequence of DNA that exist among individuals or populations of the same species. These variations are encoded in the genes and are transmitted through the reproductive cells, the sperm and egg, from one generation to the next. The specific versions of a gene, known as alleles, determine the range of traits available within a species’ gene pool, such as different blood types or variations in height.
Inherited variation must be distinguished from acquired variation, which encompasses changes that occur during an organism’s lifetime due to environmental influences or lifestyle choices. Examples of acquired traits include a scar from an injury, increased muscle mass from exercise, or the ability to speak a foreign language. These characteristics are not coded in the DNA of the reproductive cells and cannot be passed to offspring. They do not contribute to inherited variation.
Inherited traits, by contrast, are present from birth or become expressed as an organism matures because they are rooted in the genetic code. Only differences passed down through DNA have the potential to influence the makeup of future generations. This genetic inheritance provides the foundation for the diversity seen across all forms of life.
How New Variation Arises
New genetic variation arises through two primary biological processes. The first, and ultimate source of all new material, is gene mutation, which involves a random change in the DNA sequence. A mutation can be as small as a single base pair substitution, where one DNA building block is swapped for another, or it can involve larger structural changes to the chromosome.
These random changes can occur due to errors during DNA replication or from exposure to environmental factors like radiation or certain chemicals. While many mutations are neutral or even harmful, a rare few may introduce an entirely new allele into the population. This novel genetic information can potentially code for a new trait, expanding the available variation within the species.
The second primary source of variation is genetic recombination, which occurs during sexual reproduction and involves the shuffling of existing alleles. This process happens specifically during meiosis, the cell division that produces sperm and egg cells. Recombination ensures that the genetic material from the two parents is not simply blended but is instead mixed in unique ways.
One mechanism of recombination is crossing over, where homologous chromosomes exchange segments of DNA. Another factor is independent assortment, which describes the random way that pairs of chromosomes line up and separate during meiosis, creating gametes with different combinations of parental chromosomes. These processes create unique combinations of genes in the offspring. This increases overall diversity and ensures that siblings, except for identical twins, possess different sets of traits.
Observable Examples of Inherited Traits
Inherited variation manifests in many observable characteristics across the natural world, from physical features to underlying metabolic functions. In humans, one common example is eye color, which is determined by multiple genes that control the amount of melanin pigment produced in the iris. Similarly, traits like the natural texture of hair, whether straight, wavy, or curly, are dictated by inherited genes.
Beyond physical appearance, certain physiological differences, such as blood type (A, B, AB, or O), are examples of inherited traits determined by genes. The ability to roll one’s tongue into a tube shape is often cited as a trait passed down through generations. Inherited variation can also determine susceptibility to certain conditions, such as color blindness or genetic diseases.
In other organisms, inherited traits are diverse. Plant species, for example, show inherited differences in flower color, the shape of seeds, or resistance to various pathogens. In animals, inherited variation is evident in the coat patterns of mammals, such as the stripes on a zebra or the spotting on a domestic cat. These observable characteristics demonstrate the genetic differences passed down from parents to their progeny.