Heredity refers to the passing of genetic factors from parents to offspring or from one generation to the next. It is the sum of all biological processes by which particular characteristics are transmitted from parents to their offspring. Hereditary traits are determined by genes, and a single gene can have several variants called alleles. There are two copies of each gene in our cells, one from the sperm and the other from the egg. In an individual, these two copies (or alleles) are not necessarily identical. If the two copies of a gene are identical, we say that the individual is homozygous for that gene. If the two copies are different, the gene is heterozygous.
The concept of heredity encompasses two seemingly paradoxical observations about organisms: the constancy of a species from generation to generation and the variation among individuals within a species. Constancy and variation are actually two sides of the same coin, as becomes clear in the study of genetics. Both aspects of heredity can be explained by genes, the functional units of heritable material that are found within all living cells. Every member of a species has a set of genes specific to that species. It is this set of genes that provides the constancy of the species. Among individuals within a species, however, variations can occur in the form of each gene.
In humans, heredity is responsible for passing on physical traits such as eye color, hair color, and height from parents to their offspring. The complete set of genes within an organisms genome is called its genotype, while the complete set of observable traits of the structure and behavior of an organism is called its phenotype. These traits arise from the interaction of the organism's genotype with the environment. As a result, many aspects of an organism's phenotype are not solely determined by its genotype.
In summary, heredity refers to the passing of genetic factors from parents to offspring, and it is responsible for the transmission of traits from one generation to the next. It is determined by genes, which are the functional units of heritable material found within all living cells.
