HISTORY OF GENETICS
chapter 10 section 2 mendelian genetics
- Mendel’s laws: The laws of inheritance were derived by Gregor Mendel. He was 19th century Austrian monk. He was conducting plant hybridity experiments. Between 1856 and 1863, he cultivated and tested some 28,000 pea plants. His experiments brought firth two generalizations. They later became known as Mendel’s Laws of Heredity or Mendelian inheritance. These are described in his paper “Experiments on Plant Hybridization”. It was read to the Natural History Society of Brno on February 8 and March 8. 1865. and was published in 1866.
extending mendelian genetics
- Rediscovery of Mendel’s laws: Menders results were largely neglected. Even Mendel himself did not see their ultimate applicability. He thought they were only applied to certain categories of species. In 1900, however, the work was “rediscovered” by three European scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak. The exact nature of the “re-discovery” has been debated: De Vries published first on the subject. Correns pointed out Mendel’s priority after reading De. Vries’s paper.
- Role of William Bateson: The most vigorous promoter of Mendel’s law in Europe was William Bateson. He used the term “genetics”, “gene”, and “allele”. The model of heredity was highly opposed by other biologists. There were two objections on Mendel’s work:
- According to Mendel’s law heredity was discontinuous. But according to these biologists continuous variation are observable.
- Many biologists also dismissed the theory because they were not sure it would apply to all species. There seemed to be very few true Mendelian characters in nature.
4. Work of R.A. Fisher: However later work R.A. Fisher showed that multiple Mendelian factors were involved for individual traits. These multiple traits can produce a large number of results observed in nature.
S. Thomas Hunt Morgan and his assistants later integrated the theoretical model of Mendel with the chromosome theory of inheritance. It proved that chromosomes of cells hold the actual hereditary particles. They create classical genetics. It finally proved Mendel’s work.
Timeline of Notable Discoveries
1859 Charles Darwin publishes The Origin of Species
1865 Gregor Mendel’s paper, Experiments on Plant Hybridization 1903 Chromosomes are discovered to be hereditary units
1906 The term “genetics” is first introduced publicly by the British biologist William Bateson at the Third International Conference on Genetics in London. England.
1910 Thomas Hunt Morgan shows that genes reside on chromosomes, and discovered linked genes on Chromosmes that do not follm. Mendel’s law of independent allele segregation
botanical genetics1913 Alfred Sturtevant makes the first genetic map of a chromosome 1913 Gene maps show chromosomes containing linear arranged gencs
- 1918 Ronald Fisher publishes On the correlation between relatives on the supposition of Mendelian inheritance – the modem synthesis starts.1927 Physical changes in genes are called mutations.1928 Frederick Griffith dbcovers a hereditary molecule that istransmissible betwee i bacteria (see Griffiths experiment) 1931 Crossing over is the cause of recombination (see BarbaraMcClintock and cytogenetics)1941 Edward Lawrie Tatum and George Wells Beadle show that genes code for proteins: see the original central dogma of genetics
1944 Oswald Theodore Avery, Colin McLeod and Maclyn McCarty isolate DNA as the genetic material (at that time called transforming principle)
1950 Erwin Chargaff shows that the, four nucleotides are not present in nucleic acids in stable proportions, but that some general rules appear to hold (e.g.. the nucleotide bases AdenineThym Inc and (.’ytosine-Guanine always remain in equal proportions). Barbara McClintock discovers transposons in maize
1952 The Hershey-Chase experiment proves the genetic information of phages (and all other organisms) to be DNA
1953 DNA structure is resolved to be a double helix by James D. Watson and Francis Crick, with the help of Rosalind Franklin
1956 Jo Hill Tjio and Albert Levan established the correct chromosome number in humans to be 46
1958 The Meselson-Stahl experiment demonstrates that DNA is semiconservatively replicated
1961 The genetic code is arranged in triplets
1964 Howard Temin showed using RNA viruses that Watson’s central dogma is not always true
1970 Restriction enzymes were discovered in studies of a bacterium. Haemophilus influenzae, enabling scientists to cut and paste DNA
1977 DNA is sequenced for the first time by Fred Sanger, Walter Gilbert. and Allan Maxam working independently. Sanger’s lab complete the entire genome of sequence of Bacteriophage (1)-X 74:.
1983 Kary Banks Mullis discovers the polymerase chain reaction enabling the easy amplification of DNA
1985 Alec Jeffreys discovers genetic finger printing.
1989 The first human gene is sequenced by Francis Collins and LapChee Tsui. It encodes the CF–TR protein. Defects in this cause cystic fibrosis
1995 The genome of Haemophilus influenzae is the first genome •
free living organism to be sequenced
1996- Saccharomyces cerevisiae is the first eukaryote genome sequence to be released
1998 The first genome sequence for a multicellular eukaryote. C. elegans is released
2001 First draft sequences of the human genome are released simultaneously by the Human Genome Project and Celera Genomics.
2003 (14 April) Successful completion of Human Genome Project
with 99% of the genuine sequenced to a 99.99% accuracy 2006 Marcus Pembrey and Olov Bygren publish Sex-specific, male-line transgenerational responses in humans, a proof of epigenetics.