Description
This track contains information about single nucleotide polymorphisms
and small insertions and deletions (indels) — collectively Simple
Nucleotide Polymorphisms — from
dbSNP
build 151, available from
ftp.ncbi.nlm.nih.gov/snp.
Three tracks contain subsets of the items in this track:
- Common SNPs(151): SNPs that have a minor allele frequency
of at least 1% and are mapped to a single location in the reference
genome assembly. Frequency data are not available for all SNPs,
so this subset is incomplete.
- Flagged SNPs(151): SNPs flagged as clinically associated by dbSNP,
mapped to a single location in the reference genome assembly, and
not known to have a minor allele frequency of at least 1%.
Frequency data are not available for all SNPs, so this subset may
include some SNPs whose true minor allele frequency is 1% or greater.
- Mult. SNPs(151): SNPs that have been mapped to multiple locations
in the reference genome assembly. There are very few SNPs in this category
because dbSNP has been filtering out almost all multiple-mapping SNPs since
build 149.
The default maximum weight for this track is 1, so unless
the setting is changed in the track controls, SNPs that map to multiple genomic
locations will be omitted from display. When a SNP's flanking sequences
map to multiple locations in the reference genome, it calls into question
whether there is true variation at those sites, or whether the sequences
at those sites are merely highly similar but not identical.