The term “inherited” in science refers to the process by which characteristics are passed from parents to their offspring, a phenomenon broadly known as heredity. This transmission of traits is fundamental to all forms of life, ensuring that an organism resembles its parents and species. Inheritance provides the mechanism for biological continuity across generations, forming the basis for understanding biological variation and evolution.
The Physical Basis of Inheritance
The mechanism for passing traits relies on deoxyribonucleic acid (DNA), which acts as the instructional manual for building and operating an organism. DNA is organized into specific segments called genes. Each gene contains the instructions for making a particular protein or functional molecule, making genes the actual units of inheritance that dictate the potential for a specific trait.
This genetic material is packaged into structures known as chromosomes, found within the nucleus of nearly every cell. Humans possess 46 chromosomes, arranged in 23 pairs, with one chromosome from each pair inherited from each parent. This organized packaging ensures the orderly transfer of genetic information during reproduction.
Distinguishing Inherited from Acquired Traits
Inherited traits are those coded for in the DNA and are present from birth or develop predictably as the organism matures. Examples of inherited human traits include eye color, natural hair color, and blood type. These characteristics are passed on through the genetic material contributed by the parents.
Acquired traits, in contrast, are developed as a result of environmental influences, learning, or physical changes, and they are not coded into the DNA. Examples include developing muscle mass through exercise, learning a new language, or a scar from an injury. Because acquired characteristics do not alter the genetic code passed to offspring, they cannot be inherited by the next generation.
Basic Patterns of Genetic Inheritance
The transmission of inherited traits follows predictable patterns, many first described by Gregor Mendel in the 19th century. These rules of Mendelian inheritance explain how two parents contribute to the offspring’s genetic makeup. For any given gene, an organism receives two versions, called alleles, one from each parent.
These alleles interact in specific ways to determine the resulting trait. A dominant allele produces its effect even when only a single copy is present. A recessive allele will only express its trait if two copies are inherited, one from each parent. This dominant-recessive relationship explains why certain traits can appear to skip a generation.
Genotype and Phenotype: Expression of Inherited Traits
The concepts of genotype and phenotype describe the two levels at which inheritance exists. The genotype is the organism’s genetic code—the specific combination of alleles inherited from the parents. It represents the genetic blueprint for all traits.
The phenotype, conversely, is the set of all observable physical, physiological, and behavioral characteristics of an organism. It is the visible expression of the genotype, such as having brown eyes or a specific blood type. The phenotype is not solely determined by the genotype, as environmental factors can significantly influence how genetic instructions are expressed. For example, identical twins share the same genotype but may develop different phenotypes due to variations in environmental exposures.