Topic 2:5c DNA profiling

Question 1

What is a DNA profile?

Answer 1

A DNA profile is a DNA-based pattern composed of a series of DNA fragments of different sizes.

The combination of fragments is unique to an individual.
Half the fragments in a DNA profile are inherited from the mother (maternal fragments) and the other half from the father (paternal fragments).

Question 2

how do DNA profiles differ for unrelated individuals?

Answer 2

The DNA profile of an unrelated individual is different due to the variation in genotypes.

Question 3

What does VNTR stand for? and what are VNTRs?

Answer 3

Variable number tandem repeats (VNTRs), also called minisatellites, are long blocks of highly repetitive simple sequences that are non coding (generally 6-100 base pairs).
DNA profiling detects differences in the number of repeats of VNTRs between individuals

Question 4

how are VNTRs involved in DNA profiling?

Answer 4

DNA profiling detects differences in the number of repeats of VNTRs between individuals.

Question 5

In general, what has VNTR analysis been replaced by in DNA profiling?

Answer 5

VNTR analysis has been replaced by the analysis of short tandem repeats (STRs), also called microsatellites.

Question 6

VNTR = (type of satellite)

Answer 6

minisatellites

Question 7

STR = (type of satellite)

Answer 7

microsatellites

Question 8

Where are STRs located?

Answer 8

These regions are scattered throughout the genome and are made of repeated sequences of between 2-8 nucleotide bases.

Question 9

Why is STR analysis preferred over VNTR analysis

Answer 9

STR analysis takes less time than needed for VNTRs (automated systems are used) and the results provide greater certainty of identification.

Question 10

How can STRs be represented?

Answer 10

Through electrophoresis, these STRs can be represented as peaks on a different type of electropherogram.

Question 11

What is a limitation of using STR DNA profiles for evidence?

Answer 11

One limitation of DNA profiles being used as evidence is if the number of STR sites is too small, there is an increased chance that two people have the same DNA profile.

Question 12

What are SNPs? How do they occur?

Answer 12

SNPs, (single nucleotide polymorphisms) are another type of variation increasingly used in DNA profiling

These types of changes occur due to mutation from one generation to the next.

Question 13

How are SNPs identified, and what classifies something as an SNP?

Answer 13

SNPs are found throughout the genome and are identified by looking at each allele and determining if there is a sequence change between the two genes, maternal might have a G where the paternal has a T.
If more than 1% of a population does not carry the same nucleotide at a specific position in the DNA sequence, then this variation can be classified as a SNP.

Question 14

Is SNP analysis an effective method for constructing a DNA profile?

Answer 14

As there are thousands, multiple SNPs provide a reliable method for determining a DNA profile of any individual.

Question 15

Can individuals share a SNP?

Answer 15

Although an individual may share one SNP, it is extremely unlikely that two individuals will have 100 the same (except for identical twins).