genetic fingerprinting

Question 1

genetic fingerprinting relies on the fact that the genome of most eukaryotic organisms contains

Answer 1

• many repetitive, non-coding bases of DNA
• indeed 95% of human DNA is currently not known to code for any characteristics, but may yet found to be functional
• DNA bases which are non-coding are known as variable number tandem repeats (VNTRs)
• for every individual the number and length of VNTRs has a unique pattern

Question 2

VNTRs are different in all individuals except

Answer 2

• MZ twins
• and the probability of two individuals having identical sequences of these VNTRs is extremely small
• however the more closely related two individuals are, the more similar VNTRs will be

Question 3

gel electrophoresis is used to separate DNA fragments according to their size- explain how

Answer 3

• the DNA fragments are placed onto an agar gel and a voltage is applied across it
• the resistance of the gel means that the larger the fragments, the more slowly they move
• therefore over a fixed period, the smaller fragments move further than the larger ones
• in this way, DNA fragments of different lengths are separated

Question 4

the making of a genetic fingerprint consists of 5 main stages:

Answer 4

• extraction
• digestion
• separation
• hybridisation
• development

Question 5

what occurs in extraction?

Answer 5

DNA extracted from sample such as tiny drop of blood or hair root and often amplified up using PCR

Question 6

what occurs in digestion?

Answer 6

restriction endonucleases cut the DNA into fragments

Question 7

what occurs in separation?

Answer 7

• fragments of DNA separated according to size by gel electrophoresis under the influence of electric voltage
• gel is then immersed in alkali to separate the double strands into single strands

Question 8

what occurs in hybridisation?

Answer 8

• radioactive or fluorescent DNA probes are now used to bind with VNTRs
• the probes have base sequences which are complementary to the base sequences of the VNTRs and bind to them under specific conditions such as PH and temperature

Question 9

what occurs in development?

Answer 9

• x-ray film is put over the nylon membrane

- development of the x-ray film reveals dark bands where the radioactive DNA probes have attached