1. Forensic DNA

2. The Cell The smallest unit of life
The nucleus is the “brain” of the cell
contains all the genetic info the cell needs to exist & to reproduce
In most types of cells, genetic information is organized into structures called chromosomes

3. Chromosomes
In most types of cells, genetic information is organized into structures called chromosomes
usually X shaped
Y chromosome in males
23 pairs in humans
one from mother & one from father

4. Chromosomes
22 of the pairs of chromosomes are called autosomes, and they all look the same (like and ‘x’).
The other pair are your sex chromosomes, and they differ between males (XY) and females (XX).

5. Genes
Each chromosome contains hundreds to thousands information blocks called genes
Each gene is the blueprint for a specific type of protein in the body
only identical twins will have all the genes identical

6. Chromosomes Each chromosome is a single polymeric molecule called DNA
if fully extended the molecule would be about 1.7 meters long
unwrapping all the DNA in all your cells
cover the distance from earth to moon 6,000 times

7. Phenotypes
When the sperm fertilizes the egg, you get half of your chromosomes from each parent.
You get your characteristics (phenotype) based on the DNA that are contained in these chromosomes.

8. How does it work?
Your DNA is arranged into many segments called genes. These genes are usually composed of at least two alleles from your mom and dad.
Sometimes, one gene will dominate over the other: we call this complete dominance.
Ex. Tongue rolling has a dominant phenotype.
TT vs. Tt vs. tt

9. Sometimes, the genes mix together and co-exist
Sometimes, the genes mix together and co-exist. We call this co-dominance.
Ex. AB blood type
Neither A nor B dominate over one another; rather, they coexist.
We use something called the Punnett square to predict the outcome of a genetic cross (offspring genotypes and phenotypes)

10. Structure of DNA

11. Nucleotides DNA is a polymer built from monomers called nucleotides
Each nucleotide is consists of
deoxyribose
pentose sugar
phosphoric acid
a nitrogenous base

12. The phosphate
The sugar

13. Nitrogenous Bases
The Purines
Adenine (A)
Guanine (G)

14. Nitrogenous Bases
The Pyrimidines
Cytosine (C)
Thymine (T)

15. The DNA Backbone
The monomers are linked together by phosphodiester bridges (bonds)
links the 3’ carbon in the ribose of one nucleotide to the 5’ carbon in the ribose of the adjacent nucleotide

17. The DNA Double Helix DNA is normally a double stranded macromolecule
Two polynucleotide chains are held together by H-bonding
A always pairs with T
C always pairs with G

20. 5’ T-T-G-A-C-T-A-T-C-C-A-G-A-T-C 3’
In a double helix the strands go in opposite directions

21. Functions of DNA Two Functions
To transmit information from one generation of cells to the next
To provide the information for the synthesis of components (proteins) necessary for cellular function

23. DNA Fingerprinting The basic structure of everyone’s DNA is the same
the difference between people is the ordering of the base pairs
Every person can be distinguished by the sequence of their base pairs
millions of base pairs make this impractical
a shorter method uses repeating patterns that are present in DNA

24. DNA composition
DNA strands contain information which directs an organism’s development
Exons, also called encoded DNA
<1.5% of DNA is encoded

25. DNA also contains stretches of DNA that appear to provide no relevant genetic information
Introns or un-coded DNA
98.5% of DNA is “junk” DNA
Also includes Variable Number of Tandem Repeats (VNTRs)
Can contain anywhere from 20 to 200 base pairs

26. VNTRs All humans have some VNTRs
VNTRs come from the genetic information donated by parents
can have VNTRs from mother, father or a combination
will not have a VNTR that is from neither parent

27. D1 = biological daughter of both parents
D2 = child of mother & former husband
S1 = couple’s biological son
S2 = adopted son

28. Purpose of DNA Fingerprinting
Determine identity (match tissue samples)
Establish paternity

29. DNA as Forensic Evidence
Individual evidence: used to identify a single person
Trace evidence: small amount left at a crime scene
Found in saliva, blood, semen, skin, hair roots, urine (nuclear DNA)
Hair, bones, teeth (mtDNA)

30. mtDNA
Mitochondrial DNA
Inherited ONLY from the mother

31. Collection of DNA Avoid contamination while collecting DNA samples
Wear gloves; avoid sneezing or coughing
Preserve carefully
Air-dry samples
If wet, store in freezer

32. DNA Profiling
Examine an individual’s DNA sequence to develop a DNA fingerprint (this is different than a regular fingerprint!)

33. Steps of DNA Fingerprinting
1. Extraction: take DNA out of cells
2. Amplification: make copies of DNA
Use PCR (polymerase chain reaction)3. 3. Electrophoresis: DNA pieces separated within an agarose gel or capillary tube
Visible bands of DNA form a unique pattern
Pattern = “fingerprint”

34. VNTR Analysis
Usually an individual will inherit a different variant of the repeated sequence from each parent

35. VNTR Analysis PCR primers bracket the locus
PCR reaction forms a nucleotide chain from the template

36. VNTR Analysis
The length of the amplified DNA & its position after electrophoresis will depend on the number or repeated bases in the sequence

38. Analysis used 3 different VNTR loci for each suspect giving
6 bands

39. Although some individuals have several bands in common,
the overall pattern is distinctive for each

40. Suspects A & C can be eliminated
B remains a suspect