History of genetics

In ancient Greece, Hippocrates suggested that all organs of the body of a parent gave off invisible “seeds,” miniaturised components, that were transmitted during sexual intercourse and combined in the mother's womb to form a baby.

In the Early Modern times, William Harvey's book On Animal Generation contradicted Aristotle's theories of genetics and embryology.

The 1900 rediscovery of Mendel's work by Hugo de Vries, Carl Correns and Erich von Tschermak led to rapid advances in genetics.

By 1915 the basic principles of Mendelian genetics had been studied in a wide variety of organisms — most notably the fruit fly Drosophila melanogaster.

A focus on new model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of molecular genetics.

In the following years, chemists developed techniques for sequencing both nucleic acids and proteins, while many others worked out the relationship between these two forms of biological molecules and discovered the genetic code.

Hippocrates' theory (possibly based on the teachings of Anaxagoras) was similar to Darwin's later ideas on pangenesis, involving heredity material that collects from throughout the body.

[1] For both Hippocrates and Aristotle—and nearly all Western scholars through to the late 19th century—the inheritance of acquired characters was a supposedly well-established fact that any adequate theory of heredity had to explain.

Linnaeus and others (among them Joseph Gottlieb Kölreuter, Carl Friedrich von Gärtner, and Charles Naudin) conducted extensive experiments with hybridisation, especially hybrids between species.

Species hybridisers described a wide variety of inheritance phenomena, include hybrid sterility and the high variability of back-crosses.

[13] Between 1856 and 1865, Gregor Mendel conducted breeding experiments using the pea plant Pisum sativum and traced the inheritance patterns of certain traits.

In only one sentence of his historical paper, he used the term "factors" to designate the "material creating" the character: " So far as experience goes, we find it in every case confirmed that constant progeny can only be formed when the egg cells and the fertilising pollen are off like the character so that both are provided with the material for creating quite similar individuals, as is the case with the normal fertilisation of pure species.

Weismann proposed the germ plasm theory of inheritance, which held that hereditary information was carried only in sperm and egg cells.

With this knowledge, Alfred Sturtevant, a member of Morgan's famous fly room, using Drosophila melanogaster, provided the first chromosomal map of any biological organism.

A series of subsequent discoveries (e.g.[21]) led to the realization decades later that the genetic material is made of DNA (deoxyribonucleic acid) and not, as was widely believed until then, of proteins.

In 1941, George Wells Beadle and Edward Lawrie Tatum showed that mutations in genes caused errors in specific steps of metabolic pathways.

[24] In 1952, Rosalind Franklin and Raymond Gosling produced a strikingly clear x-ray diffraction pattern indicating a helical form.

[33][34] It was first hypothesised in 1986 by Walter Gilbert that neither DNA nor protein would be required in such a primitive system as that of a very early stage of the earth if RNA could serve both as a catalyst and as genetic information storage processor.

Aristotle's model of transmission of movements from parents to child, and of form from the father. The model is not fully symmetric. [ 1 ]
Sperms as preformed humans. Painting of Nicolaas Hartsoeker 1695
Blending Inheritance
Mendelian inheritance states characteristics are discrete and are inherited by the parents. This image depicts a monohybrid cross and shows 3 generations: P1 generation (1), F1 generation (2), and F2 generation (3). Each organism inherits two alleles, one from each parent, that make up the genotype. The observed characteristic, the phenotype, is determined by the dominant allele in the genotype. In this monohybrid cross the dominant allele encodes for the colour red and the recessive allele encodes for the colour white.
Diagram of Charles Darwin 's pangenesis theory. Every part of the body emits tiny particles, gemmules , which migrate to the gonads and contribute to the fertilised egg and so to the next generation. The theory implied that changes to the body during an organism's life would be inherited, as proposed in Lamarckism .
August Weismann 's germ plasm theory. The hereditary material, the germ plasm, is confined to the gonads . Somatic cells (of the body) develop afresh in each generation from the germ plasm.
Thomas Hunt Morgan discovered sex linked inheritance of the white eyed mutation in the fruit fly Drosophila in 1910, implying the gene was on the sex chromosome .