First there was Gregor Mendel, a monk who studied inherited characteristics. This was followed by Francis Crick and James Watson who unraveled the DNA molecule. This has led us to uderstanding the Human Genome sequence. This section will examine and document the events leading up to this remarkable achievement.

DNA Timeline

1866 Gregor Mendel published the results of his investigations of the inheritance of "factors" in pea plants.       1950's Maurice Wilkins (1916- ), Rosalind Franklin (1920-1957), Francis H. C. Crick (1916- ) of Britain and James D. Watson (1928- ) of the U.S. discover chemical structure of DNA, starting a new branch of science--molecular biology.           Watson and Crick made a model of the DNA molecule and proved that genes determine heredity.   1957 Arthur Kornberg (1918- ) of the U.S. produced DNA in a test tube.   1963 F. Sanger (1918- ) of Britain developed sequencing procedure for proteins. 1966 The Genetic code was discovered; scientists are now able to predict characteristics by studying DNA. This leads to genetic engineering, genetic counseling. 1972 Paul Berg (1926- ) of the U.S. produced the first recombinant DNA molecule. 1983 Barbara McClintock (1902-1992) of the U.S. was awarded the Nobel Prize for her discovery that genes are able to change position on chromosomes.   The Late 1980's An international team of scientists began the project to map the human genome. The first crime conviction based on DNA fingerprinting, in Portland Oregon. 1990 Gene therapy was used on patients for the first time.   1993 Dr. Kary Mullis discovered the PCR procedure, for which he was awarded the Nobel prize. 1994 The FDA approved the first genetically engineered food -- FlavrSavr tomatoes engineered for better flavor and shelf life.   1995 DNA testing in forensics cases gains fame in the O.J. Simpson trial. 1997 Dolly the Sheep - the first adult animal clone.   1998 Senate inquiry begins into the Clinton/Lewinsky scandal based largely on DNA evidence.   2000 J. Craig Ventor, along with Francis Collins, jointly announce the sequencing of the entire human genome.   Character Design by:

DNA Structure
DNA Structure: A rotating, wire frame model of a Watson-Crick DNA double helix. The two chains run anti-parallel to each other and contain matched pairs of nitrogenous bases: adenine with thymine (A-T), guanine with cytosine (G-C). This complementary structure allows for two identical daughter molecules to be made from a single parent molecule and is termed “semiconservative” replication, meaning one strand of the new DNA molecule comes from the original DNA.	Copyright © Eiji Suzuki, Ph.D.
Move your mouse over the image to see the animation.

DNA Replication
DNA Replication: In this animation, adenine, which is green, is the complimentary base pair for thymine, which is pink. Guanine, which is yellow forms a complement with cytosine, which is blue. Note the specific way in which the different nitrogenous bases are paired. The adenine-thymine (A-T for short) pair is formed by two hydrogen bonds and the guanine-cytosine (G-C) base pair has 3 hydrogen bonds. Adenine can only bond with thymine and vice-versa. In the same fashion, guanine and cytosine can only bond with each other. In this way, each strand is the compliment of the other and allows for the ìsemiconservativeî of DNA replication.	Copyright © Tom Wood, Ph.D.
Move your mouse over the image to see the animation.

Cell & Nucleus
Cell & Nucleus: Here we have a diagram of a typical cell from the human body. In this picture you can get a sense of where the DNA resides in the cell as well as how it is organized in the nucleus. Double-stranded DNA is organized into chromosomes. Chromosomes are situated in the nucleus and the membrane bound nucleus is found in the cell.	Copyright © The National Human Genome Research Institute

Genotype Specificity Each individual is identified by a relatively unique combination of nucleotides found in long coiled strands of DNA organized as chromosomes found in a cell’s nucleus. The number and arrangement of chromosomes in an organism is characteristic of that organism, and can be represented as a karyotype, which derived by arranging the chromosomes in pairs by size. The karyotype can be used to show differences in genetic makeup (genotype), which determines the features that person has (phenotype). Karyotypes of various humans are shown.

Normal Male Shows 23 pairs of chromosomes. Twenty two pairs are called autosomes, 1 pair is called the sex chromosomes ; XY in a male. Males are associated with secondary sexual characteristics – abundant facial hair, voice, others. Differences are also evident in the genitalia. Normal Female Shows 23 pairs as in the male, but sex chromosomes are represented by XX. Females also have different physical features from males. A Barr body is also present in cells of the female, representing an inactivated X chromosome. Klinefelter's Syndrome Three sex chromosomes are associated with Klinefelter rather than the expected 2 - XXY. These individuals are males with some development of breast tissue normally seen in females. Little body hair is present, and such person are typically tall, with or without evidence of mental retardation. Males with XXXY, XXXXY, and XXXXXY karyotypes have a more severe presentation, and mental retardation is expected. Turner's Syndrome Only 1 sex chromosome is present -X0, or X_. The expected Y chromosome is missing. Turner syndrome is associated with underdeveloped ovaries, short stature, webbed/.bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident. Down's Syndrome Normally associated with 3 copies of chromosome number 21(trisomy of chromosome 21), rather than the 2 found normally. Down syndrome is characterized by differing degrees of mental retardation, a skin fold over the eye, typically short stature, and short hands with a deep crease in the palm. Down is also known as mongolism (mongoloid).