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Single Nucleotide Polymorphisms

by Georgina Cornwall, PhD
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    00:01 regulate gene expression. Now let us take a look at another piece of this puzzle of what things do. We need to look at single nucleotide polymorphisms. Single nucleotide polymorphisms or SNPs are variations in one nucleotide at a very specific locus.

    00:20 And we can look at these SNPs and Genome Wide Association Studies to determine the functions of genes. It is all good to know what the sequence is and know where the genes are, but what do these genes do? Single nucleotide polymorphisms are being very helpful in helping us find that out. These are SNPs and they are used to tag specific genotypes. For example, if we, later on, will look at the breast cancer (2 genes) and look at how we can use an SNP to identify whether someone has the mutated copy of that or not.

    01:07 We are using them to tag genotypes. Non-coding regions that are close to the genome are often the parts that contain the single nucleotide polymorphisms, but it could actually be within a gene also, within a coding region of a gene. Generally, it is right adjacent to a gene that we are interested in. It is not in the gene itself. Usually, there are only two varieties of the alleles. If we are looking at a single nucleotide, we could have a C or a G for example.

    01:43 Single nucleotide, two different forms polymorphisms. There are many many known SNPs. It is almost an exponential number coming into the databases that are available right now. Shortly I will take you on a quick tour of one of the databases to see how these SNPs work. Lots and lots of research in this area too as we find single nucleotide polymorphisms that give us a late way to label different genetic mutations and screen for them.

    02:20 Let us look at how a single nucleotide polymorphism works. Here we have several different sections of DNA and let us look at some single nucleotide polymorphisms that we might see. For example, you could have either C or T at the first locus or you could have G or A at the second locus or you could have A or G at the third locus. These are anywhere throughout a particular chromosome and then we can perform a map of all of the places in a chromosome where there are single nucleotide polymorphism. Here is a haplotype map of single nucleotide polymorphisms found throughout this chromosome. The three that we have shown here are exhibited right in the middle of the figure and those polymorphisms may indicate the presence or absence of a particular genotype or phenotype that is not directly the polymorphism itself. So a haplotype to define that word is a pattern of linked differences on particular chromosomal segments.

    03:30 And we will look at haplotypes in action here in just a moment. Here is our BRCA2 gene.


    About the Lecture

    The lecture Single Nucleotide Polymorphisms by Georgina Cornwall, PhD is from the course Genomics.


    Included Quiz Questions

    1. A single-nucleotide polymorphism refers to the variation in a single nucleotide that occurs at a specific position in the genome.
    2. A single-nucleotide polymorphism refers to the variation in a single nucleotide that occurs at a non-specific position in the mRNA.
    3. A single-nucleotide polymorphism refers to the variation in a single nucleotide that occurs at a non-specific position in the tRNA.
    4. A single-amino-acid polymorphism refers to the variation in a single amino acid that occurs at a non-specific position in the rRNA.
    5. A single-nucleotide polymorphism refers to the variation in a single nucleotide that occurs at a non-specific position in the rRNA.
    1. …the patterns of linked differences in the specific chromosome segments.
    2. …the patterns of linked similarities in the specific chromosome segments.
    3. …the patterns of linked similarities on the different chromosome segments.
    4. …the patterns of linked differences in the specific rRNA segments.
    5. …the patterns of linked similarities on the different mRNA molecules.

    Author of lecture Single Nucleotide Polymorphisms

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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