DNA Profiling

Question 1

What is DNA Profiling?

Answer 1

Technique used by scientists to assist in identification of individuals or their relatedness based on their information provide dby their DNA

Question 2

Give some examples of situations where DNA Profiling is handy

Answer 2

• Crime scene, suspect identification
• Paternity testing
• Identification of individuals in mass disasters

Question 3

How much DNA is needed for DNA profiling and why?

Answer 3

Small amounts of DNA needed. DNA can be amplified through PCR.

Question 4

DNA from which cells can be used to extract DNA for DNA profiling?

Answer 4

Any cell in body. DNA profile is constant.

Question 5

What are the two types o DNAs that can be tested?

Answer 5

• Chromosomes (nuclear DNA)
• Mitochondrial DNA (mtDNA)

Question 6

Describe a few differences between Mitochondrial and Chromosomal DNA

Answer 6

• mtDNA is exclusively inherited from maternal line whilst chromsomal DNA is a mix of both maternal and paternal DNA
• mtDNA does not undergo recombination whilst mitochondrial DNA does
• There are numerous copies of mtDNA in each cell, only 1 opy of chromosomal DNA in nucleus

Recombination is changes risen by mutations

Question 7

What does an STR stand for?

Answer 7

Short Tandem Repeat

Question 8

What are STRs?

Answer 8

• Sequences of 2-6 base pairs that can repeat consecutively

Question 9

Where are STRs found?

Answer 9

In hypervariable regions of DNA. These are non-coding regions.

Question 10

Why are STRs used in DNA profiling?

Answer 10

They are used to differentiate DNA profiles between individuals.

Question 11

How do STRs vary in from person to person?

Answer 11

The number of repeats differentiates between unrelated individuals

Question 12

How many STR markers are tested in DNA profiling?

There are about hundreds fo locations of STRs in human DNA

Answer 12

Usually 13 sites/locations.
They are labled as STR1, STR2, STR3…

The number following STR is location number not number of repeats

Question 13

How many alleles of an STR does a person possess?

Allele is a version of the same gene/location on chromosome

Answer 13

2 alleles. One from mum, one from dad.

You always get two numbers for each STR location.

Question 14

At each STR locus a person is either heterozygous or homozygous. Explain the term Heterozygous and Homozygous in relation to STRs

Answer 14

• Heterozygous - number of repeats in the two alleles varies.
• Homozygous - number of repeats in the two alleles is same.

Question 15

What does the term locus or loci mean?

Answer 15

• Locus = location
• Loci = locations

Question 16

How are the differences in STRs in individuals identified and compared?

Answer 16

Using Gel electrophoresis.
* The number of repeats can be identified by separating the DNA by size.
* Using a DNA ladder with knwon STR repeats, STRs are identified.

Question 17

Describe the 1st step in DNA Profiling

Collecting DNA

Answer 17

• DNA is collected and cut into relevant fragmnets by restriction enzymes.
• PCR is used to amplify STRs
• Only STRs are amplified in PCR through selection of primers.

Question 18

Describe 2nd step in DNA profiling

Process of identifying STR differences

Answer 18

• Gel electrophoresis is carried out for STRs
• Each STR locus gets a lane.
• A DNA ladder is also run through for each STR locus.

Question 19

Describe 3rd step in DNA Profiling

Identifying results.

Answer 19

• Each lane will produce bands determining the number of STR repeats.
• Number of repeats are identified by checking with DNA ladder’s bands with known number of repeats.

Question 20

How many bands should each STR locus produce in a Gel electrophoresis?

Answer 20

• If heterozygous STR - 2 bands
• If homozygous STR - 1 band. (Band will be thick)

Question 21

What type of STRs would you expect to run farthest in the electrophoresis chamber?

Answer 21

The STRs with least number of repeats, as smaller strands move quicker through gel.