21.3 DNA profiling

What is a genome

Refers to all the genes/ the whole base sequence of an organism

What are the 2 types of genes that make up the genome

Exons - coding regions of DNA

Introns - non coding regions of DNA

How much percentage do each exons and introns make up the genome 

Exons 2% 

Introns 98%

Which (out of the 2 types) gene is used for DNA profiling

introns

What do introns contain that is analysed during DNA profiling

Minisatellites - VNTRs (variable number tandem repeats)

Microsatellites - STRs (short tandem repeats) 

What is the difference between VNTRs and STRs 

VNTRs = 20-50 bases long repeated 50-100 times

STRs = 2-4 bases long only repeated 5-15times 

>> STRs have much shorter repeated units 

What are VNTRs and STRs

They are short sequences of non coding DNA 

Why are introns used for DNA profiling 

Everyone has the same STRs found at same loci on chromosomes HOWEVER number of repeated units an individual has per STR is unique and different in everyone 

>> extensive variation between people 

What is DNA profiling

Technique used to identify the unique non coding regions of DNA of an individual - without reading the entire sequence

What is another name for DNA profiling 

DNA profiling = Genetic/ DNA fingerprinting 

What is a DNA profile

Image of the satellite pattern of an individual 

Why is DNA profiling used

-to help identify the suspects from a crime 

-identify the risk of genetic disorders as well as predicting its onset and severity 

-establishing paternity by comparing childs DNA profile to parents 

What is a limitation of DNA profiling

Identical twins have 100% same genome so DNA profiles would be very similar and difficult to distinguish 

Outline the process on how to create a DNA profile

1. Extract DNA sample - from a tissue e.g. blood, semen 

2. Add restriction enzymes (restriction endonucleases) - cut DNA into small fragments at recognition sites/ palindromic sites on either end of the STR

3. Amplify DNA sample with PCR - creates lots of copies 

4. Gel electrophoresis - separates DNA fragments by size using electric current applied to agarose gel matrix 

5. Alkaline solution - breaks hydrogen bonds between complementary base pairs causing dna double helix to unwind releasing the single strands 

6. Southern blotting - transfer single stranded DNA from fragile gel onto sturdy nylon membrane to make it easier for analysis 

7. Hybridisation - add radioactive or fluorescent DNA probes which will bind to complimentary satellite regions 

8. Visualise - use X rays (for radioactive probe) or uv light (for fluorescent probe) to reveal the barcode-like DNA pattern

How does DNA profiling differ from sequencing?

cheaper and faster - profiling focuses on variable non coding regions of DNA whereas sequencing looks at entire genome (coding and non coding regions)