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DNA----Forensic Science Notes
DNA: Deoxyribonucleic Acid
 *Carries genetic information
 *Makes up chromosomes in the
nucleus of a cell
 *Genes within the
chromosomes are considered
the basic unit of heredity
(Each gene has its own specific
location called a LOCUS)
 *Double stranded, double helix
shape
Remember: Humans have 46
chromosomes (23 pairs) in each
cell’s nucleus.
DNA is a polymer, arranged in
repeating units.
 *Nucleotides: repeating units of
DNA
 *Nucleotides are composed of
a sugar molecule, a
phosphorus containing
molecule, (called the
backbone) and a nitrogen
containing molecule called a
base.
 *Four types of bases: adenine,
cytosine, guanine, and
thymine.
 *Bases pair A to T and G to C
(complementary base pairing)
 *Average human chromosome
has DNA with over 100 million
base pairs
 *No order to how the bases are
sequenced on the DNA strand
Examples:
T-A-T-T
G-T-A-A
Match with:
History:
Mid 1800’s: nuclei of cells contain
nucleic acids
***Dr. Rosalind Franklin
discovered that DNA was a
strand of molecules in spiral form
***1949: Edwin Chargaff discovers
the amount of cytosine in cells
always equals the amount of
guanine & the amount of
adenine equals the amount of
thymine
***1953: Watson & Crick came up
with the double helix model of
DNA