What is the molecular unit of inheritance
The genetics (Greek geneá Descent) or Heredity is a branch of biology and deals with the structure and function of hereditary factors ("genes") and their inheritance. Inheritance is the passing on of genetic information from generation to generation. The knowledge that desired traits can be inherited has been implicitly used in animal and plant breeding for centuries. The scientific investigation of this process, however, was not tackled until the 1860s by Gregor Mendel. To do this, he is investigating self-fertilization in the garden pea Pisum sativum and described what later called gene denoted the smallest unit of inheritance. Since the discovery of the molecular basis of inheritance, a distinction has been made between several special areas of genetics:
Even if genes determine a large part of physical appearance such as size, eye color and skin color, scientific studies have shown that only 40 percent of character traits can be explained by genetic effects and 60 percent can be attributed to various environmental influences. 
History of genetics
Since ancient times people have tried to explain the laws of inheritance through various hypotheses. The Greek philosopher Anaxagoras taught around 500 BC. in preformation theory that the embryo is already preformed in the father's sperm. The sperm for female and male offspring were therefore in the different testicles. Similarly, about a hundred years later, Aristotle thought that only the man possesses hereditary disposition, while the woman has exclusively nourishing functions. Such ideas about reproduction and heredity shaped natural philosophical considerations up to modern times.
With the development of the microscope and the subsequent discovery of sperm by Antoni van Leeuwenhoek in the 17th century, important advances were made.
In 1865, the Augustinian monk Gregor Mendel discovered the fundamental laws governing the distribution of genetic makeup to descendants, which are now known as Mendel's rules. Mendel had garden pea plants (Pisum sativum) crossed with each other and observed mathematical laws by means of statistical analysis. He divided the genetic makeup into "recessive" and "dominant" genes and developed the concept of the allele. Mendel's discoveries went unnoticed and were only rediscovered at the beginning of the 20th century by Erich von Tschermak-Seysenegg, Hugo de Vries and Carl Erich Correns.
Another important development was made by Thomas Hunt Morgan in the early 20th century when he discovered that there are also traits that are mostly inherited together (linked genes that are on the same chromosome). The centiMorgan unit is named after him.
In 1953, Watson and Crick showed that the polymer DNA carries genetic information and how it is passed on. This laid the foundations for deciphering the genetic code and for the fact that today the location and function of many genes in the entire genome are known.
Milestones in Genetics
- Published 1859 - Charles Darwin The Origin of Species
- 1865 - Gregor Mendel publishes his work
- 1869 - Friedrich Miescher discovered the DNA in an extract from pus cells and named it "Nuclein"
- 1903 - Chromosomes are recognized as carriers of genetic information
- 1906 - William Bateson coined the term genetics
- 1910 - Chromosomes contain genes
- 1913 - Thomas Hunt Morgan attempts to crossbreed with the fruit flyDrosophila melanogaster by
- 1927 - Physical changes in genes are known as mutations
- 1928 - Frederick Griffith discovers that the molecules of the genetic material can be exchanged between bacteria (see Griffith's experiment, plasmids)
- 1931 - Crossing over causes recombination
- 1940 - Systematic genetic analysis of microorganisms. E.B. Ford discovers the polymorphism of genes.
- 1944 - Oswald Theodore Avery, Colin McLeod and Maclyn McCarty isolate DNA as genetic material
- 1945 - genes encode proteins (see also one gene - one enzyme hypothesis)
- 1950 - Erwin Chargaff shows that the four nucleotides do not occur in equal proportions in the DNA
- 1951 - Barbara McClintock publishes her groundbreaking research in genetics - jumping genes.
- 1952 - The Hershey Chase experiment shows that the genetic information of phages (and other organisms) is stored in DNA
- 1953 - Based on the X-ray structure analyzes by Rosalind Franklin, the DNA structure is elucidated by James Watson and Francis Crick as a double helix
- 1958 - Detection of the semiconservative replication of DNA by Meselson and Stahl
- 1961 - The genetic code is made up of groups of three (triplets), so-called codons
- 1969 - Jonathan Beckwith is the first to succeed in isolating a single gene (from E. coli)
- 1969 - Arber discovers restriction enzymes
- 1977 - Frederick Sanger introduces his dideoxy chain termination method that revolutionizes DNA sequencing
- 1983 - Kary Mullis invents the polymerase chain reaction (PCR) while driving a car
- 1997 - The first eukaryotic genome, that of baker's yeastSaccharomyces cerevisiae, is sequenced
- February 15, 2001 - As part of the human genome project, a preliminary working version of the entire human genome is presented
- April 14, 2003 - The human genome reference sequence is available for download  ready
Sources and further information
- ↑ Science Public
- ↑ Introduction to human genetics
- ↑ Site of the human genome project
- Molecular Biology of Genes. 2002, ISBN 3-8274-1349-4 (English edition: Genes, ISBN 0-13-143981-2)
- Hans Stubbe: Brief history of genetics up to the rediscovery of Gregor Mendel's rules of inheritance. VEB Gustav Fischer Verlag, Jena 1965
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