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