DNA Fingerprinting DNA Structure Review Double stranded helix
DNA Fingerprinting
DNA Structure Review • Double stranded helix shape • Basic unit is a nucleotide: • Phosphate-sugar backbone • Nitrogen bases hold two strands together by hydrogen bonds. – A bonds with T – G bonds with C • Located in the nucleus
Genetics Review • No two humans have identical DNA fingerprints (except for identical twins) – The A, T, G, C sequence is unique • Chromosomes are made of DNA and protein • A gene is a sequence of DNA that codes for a protein. – 1. 5% of DNA in our genome codes for protein – 98. 5% of DNA is “noncoding DNA” – doesn’t code for a protein (some is involved in gene regulation or gene splicing…the rest is “junk”)
Genetics review continued: • There are 23 PAIRS (46 total) of chromosomes in the nucleus of EVERY cell in the human body (except for egg and sperm) – one chromosome in each pair comes from your dad, the other from your mom. • There is also mitochondrial DNA (DNA found in the mitochondria). This is inherited from your mom
DNA Identification • Most of the human genome is the same in all humans (because we are human) • Variation in our sequences mostly exists in the noncoding DNA (98. 5% of our DNA) – Much of it is in the form of repeated base sequences. – Everyone has unique patterns of repeated base sequences. – These base sequences have different lengths and different sequences in individuals. They are called “polymorphisms”
DNA Fingerprint • Pattern of DNA fragments obtained by examining a person’s unique sequence of DNA base pairs • A DNA fingerprint is used for two main purposes: – Tissue matching (same pattern, same person) – Inheritance matching (each band of a child’s DNA fingerprint must be present in at least one parent).
Sources of DNA (see Table 9 -2 on pg. 339 in your book) • Saliva (envelope, toothbrush, bite wound, cup, cigarette butt) • Blood (only need a drop) • Seminal fluid (clothes, bedding) • Skin (weapon, tape) • Hair (or hair follicle) • Sweat (weapon, hat. • Mucous (tissue, cotton swab) • Ear wax (tissue, cotton swab, ear buds) • Urine (blanket, pillow, sheet)
Process of Electrophoresis • Use restriction enzymes • A restriction enzyme is an enzyme that cuts DNA at specific “recognition sites” • In nature restriction enzymes protect bacteria against intruding DNA (viruses) by cutting the intruders DNA (can’t function) • Use an electrophoresis apparatus to separate the cut DNA
Process of Electrophoresis continued • DNA is obtained • Copies of DNA are made using the PCR method (polymerase chain reaction). – this is just a complex way to make a ton of DNA copies • Restriction enzymes are added to cut the DNA into fragments at very specific sequences. • DNA has an overall negative charge
Process of Electrophoresis continued • Put DNA into wells of gel at the negative end of the chamber • Turn on power supply • Smaller fragments will travel faster through gel, therefore they will travel the farthest in the allotted time.
Shortest fragment
- Slides: 14