module 6 - 21.1 DNA profiling

Question 1

what is the human genome?

Answer 1

all the genetic material it contains (DNA in nucleus and mitochondria combines

Question 2

what are genomics?

Answer 2

the study of the whole set of genet instructions in the form of DNA base sequences that occur in cells of an organism

Question 3

what are chromosomes made up of?

Answer 3

hundreds of millions of DNA base pairs

Question 4

what are exons?

Answer 4

regions of DNA that code for proteins

Question 5

what are introns?

Answer 5

large non-coding regions of DNA that are removed from mRNA before its translated into a polypeptide chain

Question 6

what is satellite DNA?

Answer 6

short sequences of DNA repeated many times in introns, telomeres and centromeres

Question 7

what is a microsatellite?

Answer 7

2-4 base pairs that repeat many times (between 5-15 times)

Question 8

what are minisatellites?

Answer 8

20-50 base pairs repeated from 50 to several hundred times

Question 9

what are microsatellites also known as?

Answer 9

short tandem repeats (STRs)

Question 10

where do satellites always appear?

Answer 10

always appear in the same positions on the chromosomes but the number of repeats on each mini or micro satellite varied between individuals

Question 11

why do the number of repeats on each micro- or minisatellite vary?

Answer 11

due to different lengths of repeats are inherited from both parents

Question 12

what is satellite DNA?

Answer 12

highly repetitive DNA consisting of short sequences repeated a large number of times

Question 13

what is DNA profiling?

Answer 13

producing an image of the patterns in DNA of an individual

Question 14

what are the 5 main stages of producing a DNA profile?

Answer 14

1. extract the DNA
2. digesting the sample
3. separating the DNA fragments
4. hybridisation
5. seeing the evidence

Question 15

what is involved in “extracting the DNA”?

Answer 15

• DNA must be extracted from tissue sample
• use technique called PCR (polymerase chain reaction) which gives tiny fragment of tissue

Question 16

what is involved in “digesting the sample”?

Answer 16

• strands of DNA are cut into small fragments using restriction endonucleases (REs)
• different restriction endonucleases cut DNA at a specific restriction/recognition site
• all REs make 2 cuts, once through each strand of the DNA double helix

Question 17

what are restriction endonudleases?

Answer 17

• allow scientists to cut DNA strands at defined points in the introns
• use a mixture of restriction enzymes that leave the repeating units/satellites intact so make many mini- and microsatellite regions

Question 18

what is involved in “separating the DNA fragments”?

Answer 18

• DNA needs to be separated to form a clear pattern through electrophoresis
• the gel is them immersed in alkali to separate DNA double strands into single strands
• single strands are then transferred onto a membrane

Question 19

what is electrophoresis?

Answer 19

technique that utilises the way particles move through gel medium under the influence of an electric current

Question 20

what is involved in “hybridisation”?

Answer 20

• radioactive or fluorescent probes now added in excess to DNA fragments on the membrane
• DNA probes are short DNA or RNA sequences complementary to a known DNA sequence
• they bind to complementary strands of DNA under particular conditions of pH and temperature (hybridisation)
• DNA probes identify microsatellite regions that are more varied than larger minisatellite regions

Question 21

what is involved in “seeing the evidence”?

Answer 21

• if radioactive labels were added to DNA probes, X-rays are taken of paper/membrane
• if fluorescent labels were added to DNA probes, paper/membrane is places under UV light so fluorescent tags glow

Question 22

what is the polymerase chain reaction (PCR)?

Answer 22

• is a version of the natural process where DNA is replicated
• an excess of 4 bases (A, T, C, G), small primer DNA sequences, and the enzyme DNA polymerase are mixed in a vial that’s placed in a PCR machine
• temperature within PCR machine is carefully controlled and changes rapidly at programmed intervals
• reaction can be repeated many times within PCR machine

Question 23

why is PCR repeatability good?

Answer 23

• 30 repeats gives 1 billion copies of original DNA sample
• this is more than enough to carry out DNA profiling

Question 24

How is DNA profiling used in forensic science?

Answer 24

• PCR and DNA profiling is performed on traces of DNA left at the crime scene
• DNA traces can be obtained from blood, semen, saliva, hair roots, and skin cells

Question 25

In a UK court of law, until recently DNA was taken as evidence it 11 loci and sex marker matched. Recently this put up was to 17. Why has the number risen to 17?

Answer 25

• Loci was more than earlier DNA tests and was affordable
• producing DNA profile is much quicker now and cheaper so higher number of loci that are theoretically more sensitive and with less chance of misidentification is now affordable

Question 26

The probability that full siblings will have the same DNA profile for these 10 loci is 1 in 10,000 and of first cousins is 1 in 100 million, why?

Answer 26

• Siblings are different as a result of random gene assortment in gamete formation and random fusing of gametes
• they share up to 100% of DNA but normally have different mixture of alleles, introns etc.
• by chance some will have more genetic similarity
• cousins are less closely related, so them having same DNA profile is reduced.

Question 27

What con DNA profiling also be used to determine?

Answer 27

• Determining paternity of a child (prove or disprove family relations)
• also used in identifying the species that on organism belongs to
• determines evolutionary relationships between species

Question 28

What is the information that scientists con obtain DNA profiling from often used together with?

Answer 28

DNA sequencing to make more confident risk assessments for different diseases.