DNA profiling

Question 1

define DNA profiling

Answer 1

producing an image of the patterns in DNA of an individual

Question 2

define variable number tandem repeats (VNTRs)

Answer 2

sequence of 20-50 base pairs repeated many times that varies greatly between individuals (minisatellite)

Question 3

define minisatellite

Answer 3

VNTRs

Question 4

define microsatellite

Answer 4

STRs

Question 5

define short tandem repeats (STRs)

Answer 5

short sequence of 2-4 bases repeated a smaller number of times, varies greatly between individuals

Question 6

describe how satellite regions vary and why they can be used to identify individuals.

Answer 6

• number of repeats of each mini/microsatellite varies between individuals - different lengths of repeats inherited from parents
• more closely related = more similar patterns in satellite regions will be

Question 7

state the 5 main stages od DNA profiling

Answer 7

• extracting DNA
• digesting the sample
• separating DNA fragments
• hybridisation
• evidence analysis

Question 8

describe the events in the first stage of DNA profiling (extracting DNA)

Answer 8

• PCR is used to extract DNA from a very small sample of DNA

Question 9

describe the events in the second stage of DNA profiling (digestion)

Answer 9

• restriction endonucleases cut DNA into small fragments
• cut at a specific recognition site
• mixture is used to leave satellite regions intact

Question 10

describe the events in the third stage of DNA profiling (separating DNA fragments)

Answer 10

• cut fragments are separated to form clear pattern using electrophoresis
• electrophoresis gel is immersed in alkali to separate double strands into single strands
• strands are transferred onto nylon membrane by Southern blotting

Question 11

describe the events in the fifth stage of DNA profiling (hybridisation)

Answer 11

• fluorescent DNA probes added in excess to DNA fragments on membrane
• probes bind to complementary strands under particular pH and temp - hybridisation
• used to identify microsatellite regions that vary more than minisatellites

Question 12

what are DNA probes?

Answer 12

short DNA/RNA sequences complementary to known DNA sequence - tagged with fluorescent dye

Question 13

describe the events in the final stage of DNA profiling (analysis)

Answer 13

• X-ray/UV images taken of sample to highlight the DNA probes
• fragments give a pattern of bars (DNA profile) that is unique to every individual except identical twins

Question 14

define restriction endonucleases

Answer 14

enzymes that cut strands of DNA into small fragments

Question 15

explain the role of restriction endonucleases in DNA profiling.

Answer 15

• cut at restriction sites in introns
• leave satellites intact so fragments at end of process include mix of intact mini/microsatellite regions

Question 16

suggest how DNA profiling can be used to answer questions about identity in different situations.

Answer 16

• forensics: samples of blood, semen, saliva, hair roots extracted and compared with suspect
• paternity tests
• identification of high-risk patients: some microsatellite patterns associated with increase risk of diseases