1

Repeating lengths of 3 to 7 base pairs

Short Tandem Repeats (STR)

THO1

AATGAATGAATGAATGAATGAATG…

Varying number of repeats between individuals

2

Short Tandem Repeats (STR)

THO1 6, 8

AATG repeated 6 times

One repeat from each parent

AATG repeated 8 times

6

8

3

Short Tandem Repeats (STR)

Many known STRs

Multiplexing

Simultaneous analysis of multiple STRs

Rely on multiple STRs

4

Short Tandem Repeats (STR)

U.S.

13

U.K.

10

STRs

Probability

3

1 in 5000

6

1 in 2 000 000

9

1 in 1 000 000 000

13 1 in 100s of trillions

5

STR & Capillary gel electrophoresis

In pairs

One from mother; one from father

6

STR & Capillary gel electrophoresis

Same repeat

number from

both parents

7

Paternity & Maternity Testing

Child

Mother

Father

8

Paternity & Maternity Testing

Child

Mother

Alleged

Father

9

Cannot compare directly between 2 siblings

Same technique to prove sibling relationship

Paternity & Maternity Testing

Inherit different STR repeat

numbers from each parent

10

Sibling relationship

Sibling 2

Mother

Father

Sibling 1

11

Randomly

Half from mother; half from father

Where does your DNA come from?

Siblings will have different DNA

Except identical twins

12

One arrested for possession of drugs

Identical twins

Malaysia, 2009

Police unsure which twin was guilty

Presumption of innocence

13

Improving technology

Twin identified by missing tooth

Other methods

Identical twins do not have 100% identical DNA

Advanced techniques

More expensive

14

A series of rapes

Marseilles, France

DNA matched to identical twins

To distinguish the two twins by DNA analysis

Cost 30 million euros