Lecture 15: DNA

Question 1

What is the length of repeat units on chromosome 1?

Answer 1

16 bp

Question 2

How many different alleles can exist for the repeat units on chromosome 1?

Answer 2

27

Question 3

Why is PCR technology not suitable for RFLP DNA typing?

Answer 3

RFLP strands are too long, often numbering in the thousands of bases

Question 4

What technology is best for DNA strands under a couple of hundred bases?

Answer 4

PCR

Question 5

What is the latest method of DNA typing that emerged as the most successful?

Answer 5

Short Tandem Repeat (STR) analysis

Question 6

What is the length of short tandem repeats (STR) on the chromosome?

Answer 6

Less than 450 bases

Question 7

Why are STRs ideal candidates for amplification by PCR?

Answer 7

Due to their shortness and overcoming limited-sample size problem

Question 8

How much DNA is required for STR analysis, often equivalent to 18 DNA containing cells?

Answer 8

As little as 125 picograms of DNA

Question 9

What is the advantage of STRs over RFLP in terms of susceptibility to
degradation?

Answer 9

STRs are much less susceptible to degradation

Question 10

How can one determine the number of repeats of a specific sequence in an
STR?

Answer 10

By examining the distance the STR has migrated on an electrophoretic plate

Question 11

Why are STRs highly attractive to forensic scientists?

Answer 11

Due to the hundreds of different STRs found in the human genome

Question 12

What is the concept of multiplexing in relation to STR analysis?

Answer 12

Simultaneously extracting and amplifying a combination of different STRs

Question 13

What does capillary electrophoresis use instead of flat gels for separation?

Answer 13

Thin tubes

Question 14

What rule allows for a high degree of discrimination by analyzing a
combination of STRs?

Answer 14

Product Rule

Question 15

How is the probability of having a particular combination of STR alleles
calculated?

Answer 15

By the product of their frequency of occurrence in a population

Question 16

How many standard STRs have U.S. crime laboratories standardized on for
entry?

Answer 16

13

Question 17

What are primers in DNA replication?

Answer 17

Short strands of DNA used to target specific regions for replication

Question 18

How are DNA fragments sorted in RFLP analysis?

Answer 18

By cutting DNA with restriction enzymes and separating fragments by electrophoresis.

Question 19

Describe the role of restriction enzymes in RFLP.

Answer 19

They act as specialized scissors, cutting DNA at specific base sequences.

Question 20

What is the purpose of Southern blotting in RFLP?

Answer 20

To transfer DNA fragments to a nylon membrane for visualization.

Question 21

Explain how DNA can be characterized using electrophoresis.

Answer 21

DNA fragments are separated by size and mobility in a gel matrix

Question 22

What is the key principle behind DNA typing using RFLP?

Answer 22

Variations in repeated sequences and lengths of DNA fragments

Question 23

What are tandem repeats in DNA?

Answer 23

Portions of DNA with repeated sequences of bases, like microsatellites and minisatellites.

Question 24

How are RFLPs visualized in DNA fingerprinting?

Answer 24

By treating a nylon sheet with radioactive probes and exposing it to X-ray film.

Question 25

What is the function of DNA polymerase in DNA replication?

Answer 25

To rebuild each of the strands by adding free nucleotides.

Question 26

How can the differences in DNA length be detected in RFLP?

Answer 26

By cutting DNA with restriction enzymes and analyzing fragment sizes.

Question 27

What is CODIS and who developed it?

Answer 27

CODIS is a DNA database system developed by the FBI

Question 28

What types of DNA profiles are stored in CODIS?

Answer 28

DNA profiles from convicted offenders, unsolved crime evidence, and missing persons.

Question 29

How many profiles does CODIS currently contain?

Answer 29

How many profiles does CODIS currently contain?

Question 30

List at least 3 uses of DNA forensics mentioned in the notes

Answer 30

Link suspects with crime scenes, identify unknown victims, and establish paternity.

Question 31

What are common sources of DNA evidence at crime scenes?

Answer 31

Blood, semen, saliva, urine, skin cells, hair, bone, teeth.

Question 32

How should dried blood on a surface be collected?

Answer 32

Dried blood should be removed using a sterile cotton swab lightly moistened with distilled water.

Question 33

What precautions should be taken when handling biological evidence?

Answer 33

Wear disposable gloves, face mask, lab coat, eye protection, and shoe covers

Question 34

Why should biological evidence not be packaged in plastic containers?

Answer 34

Residual moisture in plastic containers can contribute to the growth of DNA-destroying bacteria

Question 35

What is CODIS used for

Answer 35

CODIS is used as a national DNA database.

Question 36

Describe the characteristics of Unlinked loci.

Answer 36

Unlinked loci are independently inherited and have no physical characteristics

Question 37

What is the significance of the amelogenin gene in Sex Determination by STRs?

Answer 37

The amelogenin gene helps determine the sex of an individual by showing different band patterns.

Question 38

How is sex determined using the amelogenin gene?

Answer 38

Males show two bands, while females show one band.

Question 39

Explain Y-STR analysis and its purpose.

Answer 39

Y-STR analysis focuses on markers located on the Y chromosome, useful for male identification and family relationships.

Question 40

What key advantage does Y-STR analysis offer over conventional STR analysis?

Answer 40

Y-STR analysis has simpler results, with a single band instead of two bands.

Question 41

How does DNA Fingerprinting help in criminal investigations?

Answer 41

DNA Fingerprinting can link suspects to evidence or victims through DNA profiles.

Question 42

What type of DNA is used for individual characterization apart from nuclear DNA?

Answer 42

Mitochondrial DNA is used, inherited maternally and located outside the nucleus

Question 43

Explain the difference between Mitochondrial DNA and Nuclear DNA.

Answer 43

Mitochondrial DNA is maternal and outside the nucleus, while nuclear DNA is from both parents and inside the nucleus.

Question 44

What is the role of mtDNA in forensic analysis

Answer 44

Mitochondrial DNA is used for samples where STR analysis may not be possible.

Question 45

What type of forceps should be used for picking up items of evidence?

Answer 45

Disposable forceps

Question 46

How should evidence such as cigarette butts be handled during collection?

Answer 46

With clean forceps

Question 47

Why is it recommended to use disposable forceps for evidence collection?

Answer 47

So they can be discarded after single use

Question 48

How should each item of evidence be stored?

Answer 48

In its own well-ventilated container

Question 49

What percentage of the human genome encodes proteins?

Answer 49

5%

Question 50

Define DNA polymerase.

Answer 50

An enzyme that assembles new DNA strands during replication.

Question 51

Explain the structure of a nucleotide.

Answer 51

Comprised of a sugar, a phosphate group, and a base

Question 52

What is the function of DNA in directing protein production?

Answer 52

Determines the sequence of amino acids in a protein

Question 53

Describe the complementary base pairing in DNA.

Answer 53

Adenine pairs with thymine; guanine pairs with cytosine.

Question 54

What is the role of polymerase chain reaction (PCR) in DNA testing?

Answer 54

Replicate small amounts of DNA for analysis.

Question 55

What is the significance of primers in PCR?

Answer 55

Short DNA strands used to target specific regions for replication.

Question 56

Explain the process of DNA replication

Answer 56

Involves unwinding DNA, adding free nucleotides, and polymerase synthesizing new strands.