T6 Part 1: Forensics

Question 1

Define exons

Answer 1

Parts of DNA that are genes that are expressed

Question 2

Define introns

Answer 2

Non coding DNA also known as STRs

Question 3

Define and explain what an STRs

Answer 3

Short tandem repeats
Repeats of a set of base pairs - different people have different repeats within the same STRs as other people.

Question 4

What part of DNA is used for DNA profiling

Answer 4

Introns/STRs

Question 5

Name the 2 stages involved in DNA profiling and what the purpose of each is

Answer 5

PCR - to create many copies of the same part of DNA from a sample in case the 1 original sample is damaged

Gel electrophoresis - to separate different DNA fragments to form banding that can be compared

Question 6

Explain the process of isolating DNA fragments

Answer 6

Endonucleases are enzymes that come from bacteria and are specific to different binding sites on DNA. These enzymes are used to isolate the same STRs in different samples that can be copied and compared. You obtain the same STRs by using the same endonucleases

Question 7

What is the machine that PCR is called

Answer 7

Thermocycler

Question 8

What is the polymerase used in PCR and why

Answer 8

Taq polymerase is resistant to high temperatures which are used in the thermocycler

Question 9

What step must be done before cycling and why

Answer 9

Use detergent to break down phospholipids

Question 10

Describe step 1 of PCR

Answer 10

95 degrees
High temperature used to break down hydrogen bonds between DNA strand

Question 11

Describe step 2 of PCR

Answer 11

55 degrees
Primers attach to the start of the STRs

Question 12

Describe step 3 of PCR

Answer 12

72 degrees celsius
Nucleotides line up opposite strands and Taq polymerase forms phosphodiester bonds to form the new DNA strands

Question 13

After the first two cycles of PCR how many viable strands are there

Answer 13

0

Question 14

How many cycles must the thermocycler undergo to have a correct amount of strands; and how many strands will this have produced

Answer 14

30 cycles for over a billion strands

Question 15

At what rate does the number of strands grow as the number of cycles increases

Answer 15

Doubles every time

Question 16

Describe the process of electrophoresis

Answer 16

1. Fragments of DNA cut with restriction endonucleases
2. Fragments are placed in wells in agarose gel
3. A 27v current is applied to the gel
4. DNA is negatively charged so travels up the gel towards the positive anode.
5. Larger fragments move more slowly so move a shorter distance along the gel. Larger fragments produce a thicker band
6. Nylon sheet is pressed on top to produce the banding sheet
7. Fluorescent markers are added to the DNA fragments

Question 17

How are DNA profiles produced by electrophoresis used

Answer 17

Banding of different people can be compared to see if they have bands produced at the same points to see if they have the same STR repeats

Question 18

Name three MAIN factors that can be used to calculate time of death

Answer 18

Body temperature
Rigor mortis
State of decomposition

Question 19

Explain the role of forensic entomology in determining time of death

Answer 19

Each species of insect has a specific life cycle. Determining the age of the insects present enables the time of death to be determined

Question 20

Explain the role of succession which occurs as the body decays as a factor to determine time of death

Answer 20

As the body decays, the type of insects colonising the body changes. By analising the community of species present - time of death can be determined

Question 21

How can body temperature be used to determine time of death

Answer 21

Body temperature begins to decrease after death as heat producing metabolic reactions stop.
The temperature a body is found at (between 37 and ambient) shows how much it has cooled down and this can be used to calculate how long ago the person died

Question 22

Factors that affect how to use body temp to determine time of death

Answer 22

CLOTHING
POSITION
WATER CONTACT

Question 23

How can rigor mortis be used to determine time of death

Answer 23

After death muscles begin to contract as ATP is used up and they stay contracted for a period of time. It begins 2-4hrs after death and lasts up to 36 hours

Question 24

How can state of decomposition be used to determine time of death

Answer 24

Bodies follow a pattern of decay and decomposition. By figuring out the stage of decomposition you can figure out when a person died.

Question 25

Name some things that happen as a body decays

Answer 25

Putrification
Fluids drain and body dries
Gas and liquid bubbles - liqueifying of tissues

Question 26

Why do bodies turn green

Answer 26

Sulphaemoglobin

Question 27

Explain the role of microorganisms in returning carbon back to the atmosphere when someone dies.

Answer 27

Bacteria and fungi secrete organisms that break down organic matter through respiration and this releases carbon dioxide back into the atmosphere.