Heredity: Encyclopedia II - Heredity - Biology

Heredity - Biology

In biology, heredity refers to the transference of biological characteristics from a parent organism to offspring, and is practically a synonym for genetics, as genes are now recognized as the carriers of biological information. In humans, defining which characteristics of a final person are due to heredity and which are due to environmental influences is often a site of controversy (the nature versus nurture debate), especially regarding intelligence and race.

Heredity - History of heredity in biology

It was apparent to ancient humans that offspring resembled their parents. For example, Genesis 30-46 tells how Jacob and Laban split their sheep into white and speckled varieties so they could distinguish the two to ensure none was later stolen. Although it was clear that traits were hereditary, the precise mechanism of heredity was however not clear.

Various hereditary mechanisms were envisaged without being properly tested or quantified. These included blending inheritance and the inheritance of acquired traits. Nevertheless, people were able to develop domestic breeds animals through artificial selection. The inheritance of acquired traits formed part of early Lamarckian ideas on evolution.

Charles Darwin proposed a theory of evolution in 1859 and one of its major problems was a lack of coherent hereditary mechanism. Darwin believed in a mix of blending inheritance and the inheritance of acquired traits (pangenesis). Blending inheritance would lead to uniformity across populations in only a few generations and thus would remove variation from a population on which natural selection could act. This led to Darwin adopting some Lamarckian ideas in later editions of The Origin and his later biological works. Darwin's primary approach to heredity was to outline how it appeared to work (noticing that traits could be inherited which were not expressed explicitly in the parent at the time of reproduction, that certain traits could be sex-linked, etc.) rather than suggesting mechanisms.

Darwin's initial model of hereditary was adopted by, and then heavily modified by, his cousin Francis Galton, who laid the framework for the biometric school of heredity. Galton rejected the aspects of Darwin's pangenesis model which relied on acquired traits.

The inheritance of acquired traits was shown to have little basis in the 1880s when August Weismann cut the tails off mice to find that their offspring did develop tails.

The idea of particulate inheritance of genes can be attributed to the Austrian monk Gregor Mendel who published on pea plants in 1865. However, his work was not widely known and was only rediscovered in 1901. On rediscovery of Mendel's work it was initially assumed the Mendelian inheritance only accounted for large differences, such as those seen by Mendel in his pea plants — and the additive effect of genes was not realised until Ronald Fisher's (1918) paper on The Correlation Between Relatives on the Supposition of Mendelian Inheritance. For the subsequent history of genetics, see history of genetics.

In the 1930s, work by Fisher and others resulted in a combination of Mendelian and biometric schools into the modern synthesis of evolution.

Lysenkoism in the Soviet Union emphasised incorrectly the inheritance of acquired traits. The inheritance of acquired traits appealed to the communist leaders, Lysenkoist movement being led by Trofim Lysenko. This led to food shortages into the 1960s and seriously affected the USSR.

Adapted from the Wikipedia article "Biology", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki