CATALYST Read the case study on pg 158 In your notebook, answer the following

questions in complete sentences:– How was DNA fingerprinting used in this case?– Only half of Andrew’s DNA fingerprint is the same

as his Christiana’s DNA. Is that enough to prove, beyond a doubt, that Andrew is her son?

– Why did they run a DNA fingerprint on Christiana’s other children?

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Chapter 7 DNA Fingerprinting By the end of this chapter you will be able to:

explain how crime scene evidence is collected and processed to obtain DNA

describe how radioactive probes are used in DNA fingerprinting

explain how DNA evidence is compared for matching

explain how to use DNA fingerprinting to identify DNA from a parent, child, other relative, or a non-related individual

All Rights Reserved South-Western / Cengage Learning © 2009

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Introduction and History of Introduction and History of Biological Evidence in Forensics Biological Evidence in Forensics

DNA fingerprinting, also known as DNA profiling, is used in criminal or legal cases with a high degree of accuracy.

Biological evidence such as blood, saliva, urine, semen, and hair is examined for the presence of inherited traits.

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Introduction and History of Introduction and History of Biological Evidence in Forensics Biological Evidence in Forensics

DNA is the blueprint of life and contains the genetic material of a cell.

DNA holds all the information and instructions needed for a cell to make proteins and replicate

Genetic information is stored in molecules of DNA making up structures called chromosomes

– Found in the nucleus of cells in the human body.

Rosalind Franklin– 1950’s English Chemist– Used X-ray crystallography to

create image of DNALooked like rungs, like those on a

ladder between two strands that are side by side

‘X’ shape suggested a spiral or helical molecule

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Introduction and History of Introduction and History of Biological Evidence in Forensics Biological Evidence in Forensics

Watson & Crick – 1953 used

Franklin’s picture to make an accurate 3-D model of DNA

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Introduction and History of Introduction and History of Biological Evidence in Forensics Biological Evidence in Forensics

DNA Structure

DNA = deoxyribonucleic acid

Polymer consisting of thousands of smaller, repeating units called nucleotides

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DNA Nucleotides

A DNA nucleotide is composed of three parts:1. Phosphate group: made of oxygen,

hydrogen, and phosphorous

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DNA Nucleotides

2. Deoxyribose: 5-carbon sugar made up of carbon, hydrogen, and oxygen.

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DNA Nucleotides

3. Nitrogenous base: made up of carbon, oxygen, hydrogen, and nitrogen

3. There are 4 types:

Adenine (A)

Guanine (G)

Cytosine (C)

Thymine (T)

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purines

pyrimidines

DNA Structure

DNA is made up of two strands of nucleotides that form a structure that looks like a twisted ladder which we call a double helix.

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DNA Structure

Double helix – Backbone (sides of

ladder): polymer with alternating sugar-phosphate sequence

– Connected by the nitrogenous bases held together by hydrogen bonds

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phosphate

sugar

bases

H Bond

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Base Pairings

Chargaff’s rule– Erwin Chargaff (1950)– Amount of adenine (A) equals the amount of

thymine (T)– Amount of guanine (G) equals the amount of

cytosine (C)

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Base Pairings

Complimentary Base Pairings: every base pair consists of one purine (A or G) and one pyrimidine (T or C)– Adenine (A) always pairs with thymine (T)

forming 2 hydrogen bonds A-T– Guanine (G) always pairs with cytosine (C)

forming 3 hydrogen bonds G-C

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DNA Structure

When the base pairs of the DNA strands form a double helix, the strands are considered to be complimentary– if the bases in a section of one strand is

CGTCTA, then the order of bases in the complementary section of DNA in the other strand is GCAGAT

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CGTCTAGCAGAT

DNA Structure

DNA makes up structures known as chromosomes– DNA coils into

chromosomes around proteins

– Chromosomes are found in a cell’s nucleus

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Human DNA

There are 23 pairs (total of 46) of chromosomes in the nucleus of most human cells (except sperm and egg cells)– One chromosome in each pair is inherited

from the mother and the other is inherited from the father

50% of a person’s DNA come from each parent

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Human DNA

Nuclear DNA: found in the chromosomes – Virtually identical in all cells of the human body– DNA fingerprints are derived from nuclear DNA

Mitochondrial DNA: found in the mitochondria– Only inherited from the mother– Can be used to identify a person’s mother

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Genes & Alleles

Each chromosome contains many genes– Genes: DNA sequences that have

instructions that determine our inherited characteristics of traits

Genes determine our characteristics (i.e. blue eyes, brown hair,

Used to produce proteins or RNA (ribonucleic acid)

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Genes & Alleles

We can have two versions of each gene– Allele: one of the alternative forms of the

genes– One allele comes from the mother and the

other comes from the father.Example:

– One allele codes for normal hemoglobin while the other codes for abnormal hemoglobin

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DNA

Encoded DNA (exons): DNA used to make up proteins and other molecules

Unencoded DNA (introns): DNA that does not produce proteins or RNA molecules– Important in gene splicing

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DNA

The human genome is the total amount of DNA in a cell (both nuclear and mitochondrial) There are 3 billion base pairs and 23,688 encoded genes in

the human genome– That is less than 1.5% of the DNA in the genome (more

than 98.5% is non-coding)

If you took out all of the DNA in all of your cells and stretched the strands end to end you could reach the moon…– 6000 times!23