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Genes & DNA: the science of heredity
1866 (Mendel) to 1953 (double helix) and beyond· Theory or idea· Microbes & cells
Well establishedStrong fossil, genetic or geological evidence.
The science of how traits pass from parents to offspring through genes, which are made of DNA.
See it on the Life map →What happened
Gregor Mendel's pea experiments (1866) showed that traits are inherited as separate units, later called genes. Ignored until 1900, his rules were then tied to chromosomes, threadlike bodies in the cell nucleus. In 1944 Oswald Avery's team showed genes are made of DNA, and in 1953 Watson and Crick, using Rosalind Franklin's data, found its double-helix shape. The genetic code was cracked by 1966; the human genome was read in 2003 and finished end to end in 2022.
Why it matters
Heredity was the missing piece of Darwin's theory. Genes now let scientists date splits between species, trace human ancestry and edit DNA directly.
The evidence (fossils, genes, rocks)
Breeding experiments in peas, flies and mice; microscope studies of chromosomes; X-ray images of DNA; and, since 1977, direct DNA sequencing of millions of organisms.
Still debated
How genes and environment combine to shape complex traits like height or disease risk, and what much of the DNA that does not code for proteins does.
Inside this (3)
Connections (3)
▸Genes & DNA: the science of heredity made possible CRISPR gene editingWell established
The connection
CRISPR rests on a century of genetics: knowing genes are DNA, reading their code, and sequencing bacterial genomes. Odd repeats in bacterial DNA were spotted in 1987; by 2005 researchers including Francisco Mojica realized they stored virus snippets as an immune memory. Doudna and Charpentier then turned the bacterial system into a programmable editing tool.
When and how
Repeats first noted by Yoshizumi Ishino in Japan (1987); Mojica in Spain (2005); Doudna (UC Berkeley) and Charpentier (then in Sweden) in 2012; Feng Zhang and George Church applied it to human cells in 2013.
The evidence
Each step is in published papers, and the 2020 Nobel Prize in Chemistry recognized the 2012 work.
Debates and open questions
Who deserves credit and patents is still contested; the University of California and the Broad Institute have fought over core patents for years.
▸Genes & DNA: the science of heredity supplied the missing piece of The modern synthesisWell established
The connection
Darwin's theory lacked a working account of heredity: if parents' traits blended, any new variation would be diluted away. Mendel's genes do not blend; they pass on intact, keeping variation available for selection. The 1908 Hardy–Weinberg rule and later population genetics turned this into equations for how gene frequencies change.
When and how
Mendel rediscovered in 1900; G.H. Hardy and Wilhelm Weinberg's rule in 1908; population genetics by Fisher, Haldane and Wright, 1918–1932.
The evidence
Population-genetics predictions match measured changes in real populations, from lab fruit flies to wild peppered moths.
Debates and open questions
The synthesis was built before anyone knew genes were DNA; how far molecular discoveries have changed it is still argued.
▸Gregor Mendel founded Genes & DNA: the science of heredityWell established
The connection
Mendel showed that traits pass on as discrete units in predictable ratios. Rediscovered in 1900 by Hugo de Vries, Carl Correns and Erich von Tschermak, his work became the core of a new science, which William Bateson named 'genetics' in 1905. Wilhelm Johannsen coined the word 'gene' in 1909.
When and how
Brno, Moravia, 1856–1866; rediscovery in the Netherlands, Germany and Austria in 1900.
The evidence
His 1866 paper and its rediscovery are well documented, and his basic ratios are reproduced in classrooms and labs every year.
Debates and open questions
Why his work went unnoticed for 34 years: an obscure journal, an unfamiliar mathematical style, and later hawkweed experiments that failed to fit his rules.