DNA profiling

why is sections of non-coding DNA used for DNA profiling?

-most genes are the same in humans

-using coding regions would not provide a unique profile

-non-coding DNA contain variable number tandem repeats (VNTRs) → VNTRs vary in number between individuals, producing a unique DNA profile

[Short tandem repeats (STRs / microsatellites) are repeated sequences of nucleotides that are smaller than VNTRs and can also be used in genetic fingerprinting]

process of DNA profiling

-DNA is extracted from a sample (e.g. blood, saliva) and is amplified using PCR

-sample of DNA is hydrolysed into fragments, using a restriction endonuclease→ fragments will all be different lengths

-VNTRs are used

-fragments are placed in wells of gel electrophoresis

-Gel electrophoresis separates the fragments based on their length

-shortest fragments move the furthest

-fluorescent tags are used→ DNA fragments are detected by UV light →helps visualise the bands formed

-DNA profile is compared with other samples to look for matches

uses of DNA profiling

-forensics

-disease risk analysis

explain why different individuals have different DNA profiles?

-different individuals have different numbers of tandem repeats

-different individuals have DNA fragments of different lengths

The specimen DNA was extracted from a hair found on victim. which suspect is guilty and explain why. Also explain they might not be guilty.

-suspect 1 is guilty

-suspect 1’s profile matches the the profile of specimen

-DNA from suspect 1 is identical to the specimen

might not be guilty

→hair may be planted

→more evidence is needed e.g. alibis and witnesses should be considered

limitations of DNA profile

-Close relatives may have similar DNA profiles

-Environmental contamination may occur

-A DNA match shows the person’s DNA is present, but doesn’t prove guilt or causation→ other evidence must be considered