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