DNA analysis

What is DNA? 

• The nucleus of the cell contains chromosomes that are inherited from both parents

  • Chromosomes are long chains of DNA that are tightly bound 

    • There are 23 pairs of chromosomes that make up the human genome

  • If a single strand of DNA was stretched out, it would be 6 ft in length folded up in human cell

• Humans have 35,000 genes

DO NOW: 

1. How much DNA is in the nucleus of most of your cells? 

23 chromosome pairs. If it was stretched out it would be 6 feet. 3 billion base pairs. 

2. What are the 4 nitrogenous bases? Adenine (A): Pairs with Thymine (T)

Thymine (T): Pairs with Adenine (A)

Cytosine (C): Pairs with Guanine (G)

Guanine (G): Pairs with Cytosine (C)

3. Transcribe: ATGCAGGTAT TACGUCCATA 

DO NOW:

1. Find the complementary sequence: CATGAGACCGATATCACA -GTACTCTGGCTATAGTGT

2. How was your long weekend? 

IT WAS FANTASTIC!

DNA Structure vs. Function

• DNA is arranged in double helix, with a twisted ladder like structure

  • The sides of the helix are made up of sugar and phosphate groups, which gives DNA acidic properties

  • The inside of the helix contains the base pairs, with one base pair matched specifically to another

    • Adenine-Thymine, Cytosine-Guanine

• The average DNA molecule has over 100 million nucleotides

  • For humans, the order is 99.9% similar, but there is 0.1% that makes DNA individual for every person 

• A gene is the functional part of DNA that codes for a particular protein, which performs a specific function in the body

Why can DNA serve as a fingerprint?

• DNA 'fingerprinting’ or ‘profiling’ involves identifying a person's unique genetic code

• DNA is found in every nucleated cell of the human body and can be extracted from blood, semen, urine, bone, hair follicles, and saliva

DO NOW:

1. Which of the suspects matches the specimen DNA sample?

Suspect number one matches the DNA sample

2. Name 3 things that DNA can tell investigators. Genes, physical characteristics, perpetrator, gender, health conditions, mutations

3. Why is DNA profiling referred to as “fingerprinting”? 

It is referred to as “fingerprinting” because like fingerprints it identifies individuals based on their genetic makeup.

Forensic Uses of DNA

• Blood and body fluids are the most common evidence that forensic scientists use to test for DNA 

  • A small blood sample with just a few white blood cells is all scientists need to extract DNA

• DNA samples taken from a crime scene are examined to see if they are appropriate for DNA analysis 

• If a sample is able to be analyzed, the DNA is extracted from the cells by using enzymes to break down nucleus and release DNA

What can you determine through DNA analysis?

• Identify potential suspects whose DNA may match evidence left at the crime scene

• Clear a person wrongly accused of crimes 

• Identify crime and catastrophe victims 

• Establish paternity and other family relationships. 

How does DNA analysis work?

• Step 1: Removal. 

  • DNA is removed from the material submitted to lab

    • Blood, hair, semen, saliva, skin cells (material containing a cell with a nucleus)

  • Unlike fingerprints, only a minuscule amount of genetic material is needed to identify a subject

  • The national DNA database system contains any DNA the FBI and police departments have

• Step 2: DNA Extraction

  • Cells in a sample are separated by grinding or vortexing and are put into a salt solution

    • Positively charged sodium ions protect the negatively charged phosphate groups in the backbone of DNA

  • A detergent is added and breaks down the lipids in cell membranes and nucleus and DNA is released 

  • Filtering and a protein enzyme are added to break down debris and purify 

  • Ice cold alcohol is added, allowing the DNA to be visible and be removed 

    • DNA breaks down in water, but insoluble in salt and alcohol, so can be taken out 

What is added to extract DNA and why? ↑

• Step 3: Quantitation

  • Determines how much DNA was retrieved from cells 

    • Specific amounts of DNA needed to get the best results 

  • Optical density readings taken by a spectrophotometer can determine the concentration and purity of DNA in a sample 

  • Also can use gel electrophoresis to show the presence of DNA in your sample and indicate quality.  

  • Gel electrophoresis separates DNA fragments by size. Larger fragments 

  • DNA has a negative charge!! 

• Step 4: DNA Amplification

  • Specific regions within the dna are copied thousands of times

  • PCR (Polymerase Chain Reaction) uses DNA polymerase enzymes to clone DNA and make millions of copies

    • Uses thermal cycling (repeated heating and cooling) for DNA melting and replication 

    • New DNA uses as template for replication and a chain reaction makes copies exponentially

• Step 5: DNA Sequence Detection Process

  • DNA separated by size and passed through a laser.

    • Camera records the color of the fluorescent tag and how much there is.

  • DNA profile can be made of that region or locus (location on a chromosome that contains a specific gene)

  • Gives results at 16 different loci 

    • Matches all 16 loci, it is a perfect match, placing individuals at crime scenes.This method enhances the accuracy of forensic investigations, allowing law enforcement to establish connections between suspects and crime scenes with high reliability.