Genetics is a scientific concept defined as the study of genes, genetic variation, and heredity in organisms. It is a fundamental branch of biology because heredity is vital to the evolution of organisms. The modern science of genetics began with the work of the Augustinian friar Gregor Mendel in the mid-19th century. Mendel conducted breeding experiments on pea plants between 1856 and 1865, which provided the initial evidence that traits are inherited by discrete "units of inheritance". His work solved the problem of explaining the mechanism of trait transmission, contradicting the earlier theory of "blending inheritance". The term genetics itself was coined in 1905 by William Bateson, a proponent of Mendel's work.
The mechanism of genetics centers on DNA (deoxyribonucleic acid), which is the chemical substance that genes are made of and contains the instructions for making the body work. A gene is a segment of DNA that contains instructions for building one or more molecules, such as proteins. The DNA is packaged into thread-like structures called chromosomes, and humans typically have 23 pairs of chromosomes in most cells. Individuals inherit one copy of each chromosome pair from each parent, which is how traits are passed down. The inheritance patterns are governed by Mendel's laws, such as the law of independent assortment.
Genetics is closely connected to the broader field of Genomics, which is the study of all of a person's genes, known as their genome. Other related concepts include Molecular Genetics, Epigenetics, and Biotechnology. The field has changed recently with the development of advanced genome-editing tools like CRISPR-Cas9, which was recognized with the Nobel Prize in Chemistry in 2020. This technology allows for the precise modification of DNA, leading to advancements in gene therapy and diagnostics, while the core principles of Mendelian inheritance and the role of DNA remain the same.