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forensics > chapter 10 - DNA > Flashcards

chapter 10 - DNA Flashcards

1
Q

James Watson and Francis Crick discovered

A

Developed DNA model and double helix structure in 1953

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2
Q

Rosalind Franklin discovery

A

Took first pictures of DNA

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3
Q

what is DNA

A

Code of genetic information

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4
Q

where is DNA found

A

nucleus

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5
Q

DNA helps code for

A

proteins

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6
Q

proteins give us

A

uniqueness

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7
Q

gene definition

A

fundamental unit of heredity

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8
Q

how many chromosomes does a person have?

A

46 total
23 pairs, 1 from each parent

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9
Q

chromosomes are found in the form of

A

wound up DNA

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10
Q

double helix

A

2 coiled strands of DNA

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11
Q

what are DNA strands made of?

A

nucleotides

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12
Q

nucleotide made of

A

5-carbon sugar (deoxyribose), phosphate group, nitrogenous base

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13
Q

4 base pairs of DNA and their pairing

A

adenine and thymine
cytosine and guanine

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14
Q

coding DNA

A

Codes for unique proteins

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15
Q

what percentage of DNA is coding DNA?

A

5%

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16
Q

what percentage of DNA is non-coding DNA?

A

95%

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17
Q

what does non-coding DNA code for?

A

nothing

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18
Q

what type of DNA is best for forensic identification? why?

A

non-coding DNA, contains tandem repeats that would be specific to each person

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19
Q

what is DNA replication

A

Making new DNA from existing DNA
Making more copies

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20
Q

how does DNA replication work?

A
  1. DNA helicase separates DNA strands by breaking Hydrogen bonds
  2. replication fork forms gaps in DNA ligase
  3. DNA polymerase adds complementary nucleotides to each DNA strand
  4. covalent bonds form along sugar-phosphate backbone
  5. DNA polymerase falls off
  6. replication is complete
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21
Q

what does the replication fork look like

A

Y

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22
Q

purpose of DNA fingerprinting

A

Establishes a link between biological evidence and a suspect

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23
Q

uses for DNA fingerprinting

A

Evidence in court
Body identification
Blood relative identification
Cures for disease

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24
Q

3 main technologies of DNA typing

A

RFLP
PCR
STR

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25
Q

what does RFLP stand for

A

Restriction Fragment Length Polymorphisms

26
Q

what does PCR stand for

A

polymerase chain reaction

27
Q

what does STR stand for

A

short tandem repeats

28
Q

when was RFLP used

A

1985-mid 90s

29
Q

polymorphisms definition

A

variations of DNA sequences between individuals

30
Q

4 basic steps of RFLP

A

Isolate→ separating the DNA from the cell
Cut→use restriction enzymes to cut
Separate/Sort→ use gel electrophoresis
Analyze→ looking for specific allele patterns

31
Q

what happens in the 1st step of RFLP?

A

isolation and extraction
Break open cells→grind them and add a detergent solution
Add salt→ (sodium chloride) - remove proteins bound to the DNA
Precipitate DNA→ add cold alcohol

32
Q

what happens in the 2nd step of RFLP?

A

Cut
Restriction enzymes (bacterial cells) cut DNA
Looks for specific DNA sequence (tandem repeats)

33
Q

what happens in step 3 of RFLP

A

Gel Electrophoresis
Load DNA into gel wells
Add electrical current
Molecules sort by size
Banding pattern

34
Q

what happens in the 4th step of RFLP?

A

Radioactive markers are added
Bind to DNA

35
Q

3 outcomes of RFLP

A

match
excluded
inconclusive

36
Q

DNA match definition

A

DNA profile appears the same

37
Q

DNA exclusion definition

A

samples originated from different sources

38
Q

DNA inconclusive definition

A

doesn’t support a conclusion

39
Q

what is PCR designed to do

A

Designed to copy or multiply strands of DNA

40
Q

when is PCR used

A

when there is limited evidence

41
Q

how much DNA can you get from a single speck of blood?

42
Q

primer definition

A

short segments of DNA

43
Q

how does PCR work (4 steps)

A

Heat DNA→ causes separation of DNA strands

Cool and add a primer→ allows DNA segments to find their base pair

Add DNA polymerase and free nucleotides→ causes DNA to rebuild

Heat to 75 C for completion

44
Q

advantages of PCR

A

Yields more than 1 billion copies
quick
short strands
anything can have DNA on it

45
Q

how many cycles of PCR usually happens

46
Q

how long does 1 cycle of PCR take

47
Q

why are shorter strands of DNA more advantageous in PCR?

A

they are less susceptible to degradation

48
Q

what is STR

A

Short sequences that repeat themselves in a DNA molecule

49
Q

how long is an STR

A

3-7 bases in length; less than 450 bases long

50
Q

where are STR located

A

chromosomes (loci)

51
Q

what type of DNA testing is the most successful? why?

A

STR, large numbers in the human genome

52
Q

how does STR work?

A

Extract the gene from the sample→ STR TH01→ A-A-T-G; 7 variants found→ 5-11 repeats
Amplify the sample using PCR
Separate by electrophoresis
Examine the distance the STR migrates to determine the number of times TH01 repeats
Each person has two STR types for TH01—one inherited from each parent

53
Q

how are the results of STR shown?

A

peaks on a graph
each represents the size of a DNA fragment
the possible alleles are numbered for each loci

54
Q

multiplexing definition

A

the more STR’s characterized, the smaller the percentage of population they can come from

55
Q

2 forms of sex identification in STR

A

Amelogenin gene
Y-STR’s

56
Q

Amelogenin gene

A

found on x and y chromosome
Shorter by 6 bases on the X chromosome
Males= 2 bands; females= 1 band

57
Q

Y-STR’s

A

only found on Y chromosome

58
Q

advantages of STR

A

only requires a small amount of DNA
greater discrimination of results
less susceptible to degradation
less time to run

59
Q

how much DNA do you need for STR

forensics (6 decks)

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