Heredity, the passing of traits from parent to offspring. The natural laws of heredity account for the fact that one generation of a particular plant or animal resembles preceding generations. Chicks hatch from chicken eggs and develop into chickens. Human babies are born of human beings and grow to human adulthood. More specifically, large chickens tend to have large offspring, and persons with fair skin usually have fair-skinned children.

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Not all hereditary traits, however, are as obvious as body size and shape or skin color. For example, some persons inherit color blindness, but may not even be aware of the condition. Others may inherit the tendency to develop a certain disease under certain environmental conditions.

Although heredity produces characteristics through successive generations, there are usually limited differences, or variations, between one generation and the next. Sometimes an individual will possess a hereditary trait that has not been evident for several generations. The process that makes this possible is called atavism, or reversion, and the individual is called a throwback.

Genetics is the study of the biological mechanisms by which an organism's traits are passed from generation to generation. It is concerned both with the transmission of traits and with other characteristics of genetic material.

Knowledge gained from the study of hereditary factors in disease and disease resistance has been valuable in diagnosing and treating many illnesses. Improved methods of agriculture also owe a great deal to the study of heredity. The development of hardy, disease-resistant, and high-yielding hybrid crops, such as corn, has been of immense economic value.

Heredity terms
Alleles are different forms of the same gene.
Chromosomes are tiny threadlike structures inside each cell. Chromosomes carry the genes.
DNA stands for deoxyribonucleic acid. It is the substance within the chromosomes that carries the hereditary instructions for producing proteins and RNA.
Gene expression is the process by which a cell makes a protein or RNA according to the instructions carried by a gene.
Genes are tiny biochemical units inside each cell that determine particular hereditary traits, such as eye color and blood type. Each gene is a segment of DNA that carries instructions for producing the chainlike molecules called RNA.
Genetic variation refers to the differences in inherited traits that exist among the members of a species.
Genetics is the scientific study of heredity.
Genome is a set of all the genes a species has on its chromosomes. Scientists believe the human genome consists of 20,000 to 30,000 genes.
Genotype is the underlying genetic makeup of a trait or the overall genetic makeup of an individual.
Mutation is a change in a gene. It may produce a new trait that can be inherited.
Phenotype is the observable appearance of a trait or the overall appearance of an individual.
Protein is a chemical building block in the body. Proteins exist in every cell.
RNA stands for ribonucleic acid. Similar to DNA, it plays a key role in the production of proteins.
Trait is a characteristic, such as hair color.