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A SNP is a change of a single nucleotide at a specific position on the genome. It may be substitution, insertion or deletion.
They occur once in every 300 nucleotides on average, which means there are roughly ten million SNPs in the human genome. SNPs account for more than 90% of all the variation across the human population and they are used as genetic markers. They can occur in introns and intergenic regions which do not affect human health, and exons which can affect human health.
Example: HbS is a SNP of normal haemoglobin HbA. Sickle cell trait is the result of HbS in the heterozygous form. Sickle cell anemia is the result in the homozygous form.
Uses of SNP as genetic markers: genetic screening for presence of disease genes e.g. sickle cell anemia, tracking family inheritance of disease, forensics and DNA fingerprinting, determining differences in human populations, tracking migration routes, studying human evolution.
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STR
DNA profiling (aka DNA fingerprinting):
Involves determining the identity of an individual and familial relationships. 99.9% of our DNA is common, but sections called STRs (short tandem repeats) are unique to each individual. They are sections of non-coding DNA that are repeated many times (e.g. TATATATA). Number of repeats at a specific location in the non-coding regions of DNA varies between individuals, giving rise to different DNA profiles.
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