SNPs ( Single Nucleotide Polymorphism)

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Introduction:

 DNA is a double helical structure (  looks like a ladder )that composed of a pair of nucleotide  base that lie perpendicular to the  parallel double  strand. The nucleotide  bases may be either  a Purine (Adenine 'A' /Guanine 'G') or Pyrimidine  (Thymine 'T' /Cytosine 'C') .  These  nucleotides form the base for gene code and DNA sequence. They varies from organisms  to organisms that makes the individual unique.   

SNPs:

Sometimes during the process of copying of sequence  from parents  to the progeny a typo error  may occur in a single  nucleotide  sequence  at a particular  position  know as SNP or snips .

 It is the single nucleotide  mutation  that occurs  at the specific  position  in the genome  of the individual that causes major variation among the individuals at a frequency  of >1% in the population .  All the mutation  are not SNPs since mutation  occurs  in <1% of the population .

 Its suggested that SNPs are the  key factor  for phenotypic differences and helps to determine  the response of individual to drug treatment and environmental  stress. It's also an identical marker for identifying  Gene's associated with important biology  characters and diseases. Therefore it is important in selective breeding   ,agricultural production and productivity . 


 Types of SNPs 

1.Transition  - where Purine  is replaced by Purine and pyrimidine  by pyrimidine. 

2.Transversion - where  purine  is replaced with pyrimidine  and vice versa.

3.Non coding region - its harmless .

4.Coding region - its harmful and affect the individual  . This is further of two types

 a) Synonymous - do not alter the amino acid.  

 b) Non synonymous - alter the amino acid. 

 Its may be nonsense result in stop codon or missense  result in any other amino acid change .

5.Homozygous - both the allele are same.

6.Heterozygous - both the allele are different. 


SNP development  and detection is easy by next generation sequencing platform as they are located throughout  the genome of an individual. They are sequence specific  and are reproducible. SNP marker  helps in marking the difference between  the alleles . In plant breeding  it's useful in selecting  the desirable  lines from large population  which are useful in crop improvement . It can also be used in identifying new alleles  and phylogenetic relationship between  species. By which the process of hybridization becomes easy. 

dbsnp :

Several databases are available for SNPs of which one is dbsnp. Its a SNP database from NCBI . It contain  complete SNP sequence  for Homo sapiens. Its purpose is to provide a free platform for biological researchers to use the variant in physical mapping and population  genetics  investigations and also helps in associating the genetic variation with phenotypic traits.

To use the existing human SNPs click the below link👇

https://www.ncbi.nlm.nih.gov/snp/ 

  Now the most promising marker assisted  selection in plant breeding program is carried out by SNP marker than all other dominant and co dominant markers.

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