DNA & DNA Fingerprinting

DNA Fingerprinting

Lesson Objectives

• Review DNA and it's functions

• Describe the parts of DNA used in DNA profiling

• Describe the methods of DNA Analysis

Introduction

• DNA: Deoxyribonucleic Acid

• Outside of 100% Identical twins, there are no two people who have the same DNA

• DNA analysis has been used since the 1980s to solve many investigations

  • Criminal/Victim Identification

  • Paternity/Adoption Cases

  • Accident and Disaster Victim Identification

History of Biological Evidence in Forensics

• Most techniques used in forensic DNA Analysis started as medical developments

• Karyotyping: The Analysis of Chromosomes

• DNA Fingerprint: The pattern of DNA fragments obtained by examining a person's unique sequence of DNA Base pairs

  • also called DNA Profiling

The Function & Structure of DNA

• DNA contains the all genetic material a cell needs to make proteins and replicate

  • Humans have about 20,000 genes

• Is stored on a special cell structure called a chromosome

  • Humans have 23 pairs of chromosomes (46 Total)

    • Half from Mother, Half from Father

The Function & Structure of DNA

• DNA is made up of two strands coiled around in a double-helix structure

  • The sides of the helix are called the backbone, and are made up of sugar moleucules

  • The Rungs of the helix are pairs of Nitrogen Bases Held together by hydrogen bonds

DNA Bases

• There are four total Nitrogen bases, that only form specific pairs

  • Adenine can only bind with Thymine

  • Cytosine can only bind with Guanine

• Each strand of DNA is complementary, so the base pairs line up

Amino Acids

• In humans, the order of these base pairs is 99.9% identical

  • the remaining 0.1% is what makes each person have unique DNA

• The sequence of the Bases code for Amino Acids

  • Organic compounds that contain an Amino Group (NH₂)

  • Form Proteins

The Two types of DNA

• Cells contain two types of DNA

  • Nuclear DNA: Found on the chromosomes and is inherited from both parents

    • Completely Unique

  • Mitochondrial DNA: Found in the mitochondria of cells and is only inherited from the Mother

    • Not unique

Genes & Alleles

• Genome: The total amount of genes in a cell

  • Within a genome, there are two different sections of DNA

    • Exons: DNA coded to make proteins or other molecules

    • Introns: DNA that does not produce proteins or other molecules

• About 98.5% of the genome is Noncoding DNA

  • Plays a role in how genes are spliced

Multiple Choice

Millions of Individuals have identical DNA profiles

• True

• False

Multiple Choice

The Analysis of Chromsomes is called

• Geneology

• DNAnalysis

• Karyotyping

• Chromology

Match

Match the DNA Bases to their complimentary Pairs

• Adenine

• Thymine

• Cytosine

• Guanine

Thymine

Adenine

Guanine

Cytosine

• Thymine

• Adenine

• Guanine

• Cytosine

Multiple Choice

Where is Nuclear DNA stored in cells?

• In the Mitochondria

• In the Nucleus

• On Chromosomes

• All Over the cell

Multiple Choice

Mitochondrial DNA is inherited from the father.

• True

• False

Forensic Uses of DNA

• Most of the variation in DNA is found in Noncoding regions of DNA

  • within a DNA sequence, there are sequences of base pairs that repeat

    • Even if the same sequences repeat, they may repeat different numbers of times

• Polymorphisms: The presence of variations in DNA sequences

DNA Identification

• Most of the variation in DNA is found in Noncoding regions of DNA

  • within a DNA sequence, there are sequences of base pairs that repeat

    • Even if the same sequences repeat, they may repeat different numbers of times

• Polymorphisms: The presence of variations in DNA sequences

DNA Identification

• 1984: Dr. Alec Jeffreys develops a technique to isolate and analyze variable base pairs

  • A pattern appears as a pattern of bands depending on which section of DNA is being observed

  • Because the patterns are based on variable pairs, every individual has a unique pattern

DNA Identification

• There are two main methods of DNA Profiling that look at different types of polymorphisms

  • Variable Numbers of Tandem repeats (VNTR)

  • Short Tandem Repeats (STR)

VNTR vs. STR

• Within the noncoding sections of DNA, some sequences are repeated multiple times

  • Example Sequence: CATACAGAC

    • Person A might have three copies, while Person B might have seven

• The length of a VNTR can vary from 9 to 80 Bases in Length

• An STR is a sequence of DNA that repeats in the noncoding DNA

  • Much Shorter than a VNTR, only two to five bases long

  • Are easier and quicker to read than a VNTR

DNA Profile

• A complete profile of DNA uses a combination of both VNTR and STR to identify a person

• Can serve two main purposes

  • Tissue Matching: Two Samples are matched to the same person

  • Inheritance Matching: parts of one sample are matched to a relative

    • Must follow rules of inheritance: 50% with a parent, 25% with a grandparent

Sources of DNA

• DNA can be left at a crime scene in many different ways

  • Saliva, Blood, Skin, etc.

• Oftentimes, there is a small amount of DNA left at a scene that risks being damaged by testing

  • Polymerase Chain Reaction (PCR): a technique that creates billions of copies of DNA samples

    • Used to make enough copies of DNA to do multiple tests

    • Can be used years later to do modern tests

Multiple Choice

Which type of polymorphisms involve DNA sequences that range in length for 9 to 80 Baes

• STR

• VNTR

• PCR

• VWR

Multiple Choice

Half of the Bands in a baby’s DNA fingerprint come from their

• Uncle

• Cousin

• Father

• Grandfather

Stepls of DNA Fingerprinting

• Extraction: DNA is isolated and prepared for testing

• Restriction: A DNA Sequence is taken and cut into pieces using Restriction Enzymes that recognize patterns and cut in specific locations

  • Different Enzymes cut at different locations

• Amplification: PCR is used to make copies of chosen fragments

• Electrophoresis

Electrophoresis

• Some of the DNA fragments are loaded into an electrophoresis machine

  • Pass an electric current through the gel, causing the fragments to move from the negative end to the positive end

  • Special Stains are added to the samples to highlight sections of DNA

  • DNA Probes can cause some strands to glow

• Shorter bands move faster while longer bands move slower

Drag and Drop

​

Placeholder

DNA Bands move slower through an electrophoresis machine.

Drag these tiles and drop them in the correct blank above

Longer

Shorter

Older

Younger

Multiple Choice

DNA restriction enzymes

• are used to repair DNA

• are involved in DNA synthesis

• restrict DNA from being amplified

• cut DNA into fragments of different lengths

Labelling

A hospital had three babies born on the same day. Unfortunately, they had a mixup during bathing the babies and the identification bracelets were lost. Determine which Baby belongs to which family

Drag labels to their correct position on the image

Baby 1

Baby 3

Baby 2

Multiple Choice

Which technique is used to amplify DNA for analysis

• PCR

• STR

• KTM

• RNA