1. DNA Deoxyribonucleic Acid

2. DNA Review Genetic material (DNA) is found in the nucleus of cells, and is contained on chromosomes. An organism inherits chromosomes from each parent DNA’s main purpose is to control a cell’s function and does this by making proteins (amino acids) DNA also stores information such as hair color, eye color and other heritable traits Chromosomes are made of long, threadlike strands of genes, which are sections of DNA that code for specific instructions A human cell contains 23 pairs of chromosomes (46 total)

3. DNA Review DNA is made up of nucleotides which have 3 parts: a sugar (deoxyribose), phosphate and a nitrogenous base The four bases are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G) Complimentary bases bind with each other in the center of a DNA molecule: Adenine and Thymine are complimentary, Cytosine and Guanine are complimentary Hydrogen bonds connect the complimentary bases to each other

4. DNA Review DNA is formed of 2 strands that are complimentary to each other, and they form a double helix structure (a twisted ladder shape) The two DNA strands are composed of 3” and 5” ends, in which the 3” and 5” occur on opposite ends of the complimentary strands

5. Find the complimentary strand of DNA 3” GTAACTGGTCATTGATCT 5”

6. DNA…for Forensics DNA sequences are used to identify perpetrators, fathers in paternity tests, and exonerate suspects. These methods are called DNA “fingerprinting” or DNA “profiling” because everyone has a unique genetic code DNA can be extracted from any nucleated cell, as well as blood, semen, saliva, urine, hair, and hair follicles

7. RFLP If a DNA sample is taken from a victim, weapon or other object, it must first be processed before it is useful First the DNA must be isolated and removed from other macromolecules in cells Then DNA is given enzymes to allow it to unwind from its chromosome form DNA can then be fingerprinted using RFLP: Restriction enzymes are used to cut DNA into Fragments that are many different Lengths and exhibit Polymorphisms (many shapes)

8. R-Restriction Enzymes In order to find the unique sequence of DNA, it is first cut into smaller pieces by restriction enzymes. Restriction enzymes recognize specific sequences in the DNA and cut it at a specific point For instance, restriction enzyme EcoRi cuts DNA whenever it finds the sequence GAATTC, and cuts the DNA between the G and A

9. Electrophoresis Once restriction enzymes have split the DNA strands into different sized fragments, the fragments are separated according to size by electrophoresis The fragmented DNA is inserted into a gel and voltage is applied. As the fragments travel down the gel, they are separated by size, giving a DNA fingerprint of that individual. The gel is stained and analyzed for comparison to other DNA samples

11. Electrophoresis Smaller fragments of DNA will travel farther in the gel than larger fragments of DNA Significance: Since every person has an individual DNA sequence, it will be cut by restriction enzymes in different places. Therefore every person will have different sized fragments of DNA, and when separated through electrophoresis, create a unique DNA fingerprint (banding pattern) in the gel.

12. What is the chance of someone else having the same DNA fingerprint (fragments of the same length)? Forensic scientists also calculate the probability (chances) that another person could have the same DNA fingerprint and use that likelihood to isolate/accuse/exonerate a suspect.

13. PCR-Polymerase Chain Reaction In many crime scenes, the amount of DNA evidence is not enough to perform RFLP and electrophoresis to find a DNA fingerprint. PCR is used to take a very small sample of DNA and make millions of copies of it in a very short amount of time. Like in RFLP, the small DNA sample must first be processed by enzymes to uncoil it from chromosomes before PCR is performed

14. PCR-the steps 1. The 2 DNA strands separate as the sample is heated, the heat breaks the hydrogen bonds holding the strands together 2. It is then cooled and a primer is added which begins the process of DNA replication 3. The enzyme DNA Polymerase is added with a lot of free nitrogen bases (A, T, G, C) and the mixture is then heated again, new DNA strands are made complimentary to the original separated strands 4. At the end of one cycle of PCR, one original strand of DNA is replicated and results into 2 identical strands of DNA

15. PCR One cycle of PCR takes only about 2 minutes, to completely replicate a sample of DNA It takes about 3 hours to make 1 million copies of DNA, also known as amplifying DNA Once amplified, the DNA can then be processed using restriction enzymes and electrophoresis

16. Short Tandem Repeats (STR) DNA is made of billions of base pairs, some of which is useful and some not. The portions of DNA that code for traits, make proteins, and regulate cell activity is part of coding DNA because it is used for specific functions. A lot of DNA does not have a use and those sections of DNA are called non-coding DNA. Short Tandem Repeats are specific sequences of DNA bases (2-10 bases long) that repeat themselves at certain locations of chromosomes

17. Short Tandem Repeats (STR) STRs occur on almost every human chromosome. The number of times a specific sequence (STR) repeats is inherited from a person’s parents. For example, at a specific location on a chromosome, one STR could repeat 8 times, and another STR could repeat 11 times. So they inherited the same number of STRs for that location from each parent, one from their mother, one from their father.

18. STRs Analyzing STRs from a person’s DNA is becoming more common than RFLP because looking at STRs takes less time and is better at excluding possible suspects. The FBI analyzes 13 chromosomal locations for STRs to create a DNA profile of a person. The STR locations are named after the chromosome they are on (D18S11). Scientists also calculate the probability of another person having the same STRs at the same locations to identify a probable DNA match

19. Find the STR CTAACGATAG ATAGATAGAT AGATAGATAG ATAGATAGAT AGATAGATAG ATAGACAGAT

20. Mitochondrial DNA Recall that mitochondria are found in cells which make ATP. Mitochondria contain their own set of DNA (called mtDNA) that is only inherited by a person’s mother, not from both parents like nuclear DNA. Mitochondrial DNA also remains relatively unchanged as it is passed down. However it is relatively impossible to distinguish individuals apart that have the same mother.

21. Mitochondrial DNA Being able to analyze mtDNA is costly and takes more time than many other methods. However it can be processed with small, degraded amounts of DNA For cases in which teeth, bones and hairs may be all that’s left of a victim, mtDNA analysis is better suited. For instance, if a hair is pulled from its root, nuclear DNA can be obtained (blood, skin cells), however if only partial strands are present, mtDNA can be obtained from the hair.