Heredity is the biological process through which living organisms pass traits from one generation to the next. This explains why offspring often resemble their parents, inheriting various characteristics. It involves the transfer of genetic information, acting as a blueprint for an organism’s development and functions.
Understanding Dominant and Recessive Traits
At the core of heredity are genes, which are segments of DNA that contain instructions for building and maintaining an organism. These genes are responsible for specific traits, such as eye color or hair texture. Each gene can exist in different versions, known as alleles. For most genes, an individual inherits two alleles, one from each parent.
The interaction between these two alleles determines how a trait is expressed. A dominant allele expresses its trait if present, even with only one copy. It masks the presence of another allele. For instance, if an allele for brown eyes is dominant, having just one copy results in brown eyes.
Conversely, a recessive allele expresses its trait only if two copies are present. For example, blue eyes are a recessive trait, meaning an individual must inherit a blue-eye allele from both parents to have blue eyes.
How Genetic Traits Are Passed On
The combination of alleles an individual possesses for a specific gene is called their genotype. This underlying genetic makeup influences the observable characteristics, or phenotype, of an organism. While genotype is directly inherited, phenotype can also be influenced by environmental factors.
When an individual has two identical alleles for a particular gene, they are said to be homozygous for that trait. This can be homozygous dominant (two dominant alleles, e.g., BB for brown eyes) or homozygous recessive (two recessive alleles, e.g., bb for blue eyes). If an individual has two different alleles for a gene, they are heterozygous (e.g., Bb).
A heterozygous individual (e.g., Bb) will exhibit the same phenotype as a homozygous dominant individual (BB). For instance, a person with one allele for a widow’s peak (dominant) and one for a straight hairline (recessive) will have a widow’s peak. Only individuals with two recessive alleles will display the recessive trait, such as a straight hairline or attached earlobes.
Examples of dominant traits include brown eyes, dark hair, freckles, dimples, a widow’s peak, and unattached earlobes. Recessive traits include blue eyes, blond or red hair, no freckles, no dimples, a straight hairline, and attached earlobes.