The material in living beings that is responsible for the inheritance of characteristics is called genetic material.
The molecule of genetic inheritance must possess four major characteristics:
•Storage of information
•Expression of information
•Variation by mutation
•Pre-Mendelian ideas on heredity
1859 Charles Darwin Published The Origin of Species.
•1865 Mendelian Inheritance
•Classical genetics 1900 Hugo de Vries, Carl Correns and Erich von Tschermak
1903 Chromosomes are discovered to be hereditary units
1905 British biologist William Bateson coins the term "genetics"
1908 Hardy-Weinberg law derived.
1910 Thomas Hunt Morgan shows that genes reside on chromosomes
1913 Alfred Sturtevant makes the first genetic map of a chromosome
1913 Gene maps show chromosomes containing linear arranged genes
1927 Physical changes in genes are called mutations
1928 Frederick Griffith transformation experiment
1931 Crossing over is the cause of recombination
1941 Edward Lawrie Tatum and George Wells Beadle show that genes code for
Mutation and adaptation:
Jean-Baptiste Lamarck (1744-1829)
• Proposed “inheritance of acquired traits” ~1801; induction by the environment; also known as transformism or transmutation.
• Ideas largely ignored or attacked during his lifetime.
• Never won the acceptance and esteem of his colleagues and died in poverty and obscurity.
• Today Lamarck is associated with a discredited theory of heredity (but Lamarckism persisted until 1930s/1940s).
Charles Darwin (1809-1882)
• Heritable adaptive variation results from random mutation and natural selection (1859, The Origin of Species).
• Contrary to Larmarck, inheritance of adaptive traits does not result from induction by environmental influences.
• But differential survival (selection) and heritable variation (originally arising from mutation).
• Years following Darwin and rediscovery of Mendel resulted in controversy (until 1930s/1940s) about the relative importance of mutation and selection.
Experimental test of Lamarck’s “inheritance of acquired traits”
Salvador Luria and Max Delbrück (1943)
• An E. coli population started from one cell should show different patterns of T1 resistance depending on which theory is correct.
1. Adaptive theory states that cells are induced to become resistant when T1 is added; proportion of resistant cells should be the same for all cultures with the same genetic background.
2. Mutation theory states that random events confer resistance to T1; duplicate cultures with the same genetic background should show different numbers of T1 resistant cells.
Fig. Fluctuating populations of E. coli infected with T1 phage.Luria and Delbrück (1943)
Adaptive theory prediction: proportions or resistant cells are the same
Mutation theory prediction: proportions are function of genotypes
• Formulated basic laws of heredity during mid 1800’s
• Austrian Botanist and monk
• Experimented with peas
Mendel• Studied inheritance of seven pairs
of traits• Bred and crossbred thousands of
plants• Determined that some traits were
dominant and other recessive
Mendel• Findings were published in
• Largely ignored for 34 years
Johan Friedrich Miescher
• Swiss Biologist• Isolated nuclei of white blood
cells in 1869• Led to identification of nucleic
acid by Walter Flemming
Walter Sutton• Determined in 1903 that
chromosomes carried units of heredity identified by Mendel
• Named “genes” in 1909 by Wilhelm Johannsen, Danish Botanist
Thomas Hunt Morgan• Studied genetics of fruit flies• Early 1900’s• Experimented with eye color• His work contributed to the
knowledge of X and Y chromosomes
Thomas Hunt Morgan• Nobel Peace Prize in 1933 for
research in gene theory
Griffith's Transformation Experimen(1928)
Avery, MacLeod and McCarty Experiment (1944)
Fraenkel-Conrat and Singer (1956)
•The DNA era 1944 Oswald Theodore Avery, Colin McLeod and Maclyn McCarty prove DNA as
the genetic material
1950 Erwin Chargaff
1950 Barbara McClintock discovers transposons in maize
1952 Hershey-Chase prove the genetic material of phages to be DNA
1953 James D. Watson and Francis Crick DNA structure is a double helix
1958 Meselson-Stahl demonstrate that DNA is semiconservatively replicated
1961The genetic code is arranged in triplets
1970 Howard Temin showed using RNA viruses that Watson's central dogma is not
1970 Restriction enzymes discovered
•The genomics era
1977 Fred Sanger, Walter Gilbert, and Allan Maxam sequenced DNA
1985 Kary Banks Mullis discovers the polymerase chain reaction
1989 Francis Collins and Lap-Chee Tsui, sequence the first human gene encoding the
CFTR protein, defects in this gene cause cystic fibrosis
1995 The genome of of a free living organism Haemophilus influenzae sequenced
1996 Saccharomyces cerevisiae is the first eukaryote genome sequence to be released
1998 The first genome sequnce 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 genome
sequenced to a 99.99% accuracy
Erwin Chargaff (1950)
Erwin Chargaff was a biochemist who first figured out the equation for the different bases. He concluded that:
• The amount of adenine (A) will always equal the amount of thymine (T).
• The amount of guanine (G) will always equal the amount of cytosine (C).
• The sum of the purines (A+G) equals the sum of pyrimidines (C+T).
• The ratio [C+G] / [A+T] was typically less than unity (that is, [C+G] is less abundant).
The X-Ray photograph shows the diffraction pattern of a crystallized DNA molecule. The cross pattern in the middle is characteristic of a helical molecule with regular repeats; the broad bands at top and bottom give some indication of the periodicity.