6.3.3 DNA profiling

Question 1

how was DNA profiling developed

Answer 1

= alec jeffrey’s locating tandem repeat sequences in DNA (1978)

Question 2

define tandem repeats

Answer 2

= repetitive segments of DNA which don’t code for proteins

• between 10-100 base pairs long
• feature same core sequence (GGGCAGGAXG) = X is any of 4 nucleotide bases
• some types are highly variable (variable number tandem repeats - VNTRS)

Question 3

what did alec jeffrey’s do

Answer 3

• obtained DNA from lab technician/her parents & analysed it
• number of tandem repeats showed family resemblance
• DNA profile for each family member was unique
• concluded someone’s DNA profile could confirm/refute maternity & paternity

Question 4

procedure for DNA profiling

Answer 4

1. DNA obtained from individual (eg. mouth swab, blood, hair)
2. DNA digested with restriction enzymes = cuts DNA at specific recognition sites into fragments (vary in size between individuals)
3. fragments separated by gel electrophoresis & stained (largest fragments travel shortest distance in gel)
4. banding patttern shown
5. DNA to which individual’s is being compared is treated with same restriction enzymes & subjected to electrophoresis
6. banding patterns of DNA samples compared

Question 5

which method of DNA analysis is no longer used

Answer 5

= involved restriction fragment length polymorphism analysis (1st method)

• laborious & no longer used

Question 6

which method of DNA profiling/analysis is used today

Answer 6

short tandem repeat (STR) sequences of DNA

Question 7

method for STR sequences of DNA

Answer 7

1. sequences separated by electrophoresis
2. each STR is polymorphic (2+ different forms)
3. 13 STRs analysed simultaneously

Question 8

describe method using STR sequences to analyse DNA

Answer 8

• exact number of STRs varies between individuals
• technique is very sensitive (contaminating samples must be avoided)
• DNA can be stored for many years if crime case unsolved = later used to assess new evidence

Question 9

applications of DNA profiling

Answer 9

1. forensic science = brought about convictions & established innocence of many suspects/those wrongly convicted
   - eg. identify nazi war criminals hiding in south america, identify victims body parts after plane crashes/natural disasters (etc.)
2. analysis of disease
   - protein electrophoresis can detect haemoglobin type & aid diagnosis of sickle cell anaemia
   - varying numbers of repeat sequences for conditions (eg. huntingtons disease) can be detected using electrophoresis