[21.5] genetic fingerprinting

Question 1

what are variable number tandem repeats (VNTRs)?

Answer 1

intron sections of chromosomes made up of small numbers of bases which repeat

Question 2

how are VNTRs unique to an individual?

Answer 2

• which VNTRs are present and the number of repeated bases in each VNTR varies between people
• closer related individuals have more similar VNTRs
• the number of repeats may differ between two individuals, but not necessarily the repeating sequence

Question 3

what is gel electrophoresis used for?

Answer 3

to separate DNA fragments according to their size

Question 4

describe the process of gel electrophoresis (5)

Answer 4

1. small DNA fragments placed on an agar gel
2. voltage is applied across it
3. DNA is negatively charged so will move to the positive electrode
4. resistance of the gel means that the larger the fragment, the more slowly they move
5. smaller fragments move further than larger ones

Question 5

what are the 5 main stages of making a genetic fingerprint?

Answer 5

1. extraction
2. digestion
3. separation
4. hybridisation
5. development

Question 6

genetic fingerprinting: extraction

Answer 6

• DNA is extracted from the sample
• increase quantitity of sample using PCR

Question 7

genetic fingerprinting: digestion

Answer 7

• cut the DNA into fragments using restriction endonucleases
• RE must leave VNTR regions intact
• must use the same REs on all samples for comparison

Question 8

genetic fingerprinting: separation

Answer 8

• fragments of DNA are separated by gel electrophoresis
• gel is immersed in alkali to separate the double strands into single strands

Question 9

genetic fingerprinting: hybridisation

Answer 9

• add radioactively / fluorescently labelled probes complementary to the VNTR base sequences to identify them
• repeat with different probes, which bind to different target DNA sequences

Question 10

genetic fingerprinting: development

Answer 10

• visual signal from probes correpsond to the position of the DNA fragments separated during electrophoresis
• pattern of bands revealed is unique to every individual except identical twins

Question 11

what can genetic fingerprinting be used for? (5)

Answer 11

• relationship testing (mostly paternity)
• genetic variation testing
• forensic crime scene investigation to identify offender
• medical diagnosis for genetic diseases
• plant / animal breeding for particular alleles of a desirable gene