A Brief History Of Genetics

Around 6000 BC in Asia Minor it was observed that features were passed from parent to child.

The Ancient Greek philosopher Aristotle thought that children were made by 'The Substance' which was found in women and 'The Form' which came from men, the latter having a magical influence on the former. He believed that things gradually changed from plants, through animals, to the highest form, humanity. This is the first recorded theory of evolution.

In the 1500s and 1600s people began the classification of plants and animals into different species which led to the theory that species were created at the beginning of time and would never change.

One theory in the 1600s was that of a Dutch scientist named Antoni van Leeuwenhoek who thought that life was created spontaneously from decaying matter when he observed flies appearing out of refuse.

Later in the 1600s discoveries of the existence of the female egg and male sperm were made. It was believed that the sperm contained a tiny completely formed human being, or homunculus. This theory was called preformationism.

Dutchman Regnier de Graaf suggested in 1672 that the sperm and egg united in some way and that both were responsible for appearance and character. This theory was not accepted for many years.

William Harvey's experiments in the 1600s proved that blood circulated around the body and that the unborn embryo in deer grew larger and more complex as the pregnancy progressed. However the results of his experiments were not accepted until the 700s.

In the 1700s German scientist Caspar Wolff disproved preformationism. He carried out experiments which showed that plants and animals grew from material which looked nothing like the final plant or animal.

Jean-Baptiste Lamarck published Philosophie Zoologique in 1809 in which he put forward the theory that living creatures had an in-built desire for improvement, such as birds producing stronger muscles for flying, and these improvements would be passed on to the offspring. This supported pangenesis, the long held belief among scientists that tiny, complete, but invisible copies of all the organs in the body were put into the bloodstream by the sex organs.

Pangenesis was disproved by the experiments of German scientist August Weismann who thought that complex creatures had two sorts of tissue; somatoplasm which is needed to make the creature work and changes to which could not be inherited, and germplasm, changes to which could be inherited.

During the 1800s German zoologist Theodor Boveri showed that when cells divided, a process called mitosis, both resulting cells had an exact copy of the number and type of chromosomes in their nucleus.

Charles Darwin had probably completed his theory of evolution in 1839 but it was not until 1859 that he published his book On the Origin of the Species by Natural Selection. One reason for the delay is likely to be that he knew it would be an unpopular theory. His theory is basically that if any small difference gave one member of a species an advantage over another then that would make its chances of surviving and breeding greater, and if that difference is passed to offspring then their chances of survival are also greater. This later became known as the survival of the fittest.

For example, according to Lamarck, if feeding giraffes are unable to reach the branches of a tree then they will develop longer necks, whereas according to Darwin the giraffes with shorter necks would die out and only those with necks long enough would survive and pass the characteristic to their offspring.

Darwin was never able to show natural selection occurring and died believing all the issues were unsolved, however in 1865 Czechoslovakian Gregor Mendel published the results of his experiments with plant hybridization and his law is the foundation of modern genetics. Mendel's Law is accepted as being one of the most important biological discoveries of all time.

In 1869 Sir Francis Galton (who happened to be Charles Darwin's cousin) suggested that if identical twins inherit identical characteristics then any differences between them must be due to environmental differences. It was he who is responsible for the idea that a species can be improved by selective breeding, which became known as eugenics. He also discovered that fingerprints are unique.

Swiss biochemist Friedrich Miescher researched into the chemical structure of cells in the late 1800s.

In 1902 American biologist Walter Sutton was the first to suggest that chromosomes contained the necessary factors for heredity in his publication Chromosome Theory of Inheritance.

Following this, British biologist William Bateson discovered the principle of linkage which states that several factors are always found together on every chromosome which is made up of groups of these factors which 'are linked together and cannot behave independently'.

In 1909 these hereditary factors were named genes by Danish botanist Wilhelm Johannsen.

In 1904 American Thomas Hunt Morgan began using Bateson's work as the basis for his research and with a group of students developed the idea of a chromosome being made up of genes arranged in a long line, linked together in groups.

Deoxyribonucleic Acid (DNA) was established as genetic material in 1944 by American biologists Oswald T. Avery, Colin Macleod and Maclyn McCarty at the Rockefeller Institute in New York. They were able to show that DNA fragments from one variety of bacteria could enter the cells of another variety and change its heredity.