making the dna profile- lqc 2a

Question 1

a dna sample must first be obtained. state some possible sources of dna for forensic purposes

Answer 1

any biological tissue from plants or animals can be used. cheek swab cells, white blood cells in a blood smear, bone marrow in a skeleton, sperm, skin, hair, saliva and sometimes fingerprints

Question 2

outline how dna is extracted from cells

Answer 2

the cell membrane is disrupted in a buffer solution containing salts and detergent. the dna is separated from the rest of the cellular components by centrifugation. the sample is incubated with proteases. the dna is precipitated out and washed by using ice- cold ethanol

Question 3

how were restriction enzymes (or endonucleases) used in the original dna profiling procedure

Answer 3

to cut the STR sequences from the dna sample

Question 4

Describe how they identify where to cut DNA

Answer 4

They cut at a specific recognition site – a specific base sequence 4 to 6 base pairs long. These sequences are palindromic when double stranded i.e. GAATTC. If cut between the G and A a ‘sticky end’ is produced. If cut between the A and T a ‘blunt end’ is produced. Each restriction enzyme will only ever produce a sticky or blunt end, never both

Question 5

Why were restriction enzymes so useful in producing a DNA profile?

Answer 5

If the same restriction enzyme is used to cut the same DNA sample or two DNA samples from the same individual the fragments produced will be identical in every case

Question 6

state the technique used to copy STR sequences in modern dna profiling

Answer 6

polymerase chain reaction (PCR)

Question 7

state the technique used to separate the STR sequence fragments

Answer 7

gel electrophoresis