f53a35ac112b3b7c1410c626c974476ea9cd0541 jnavarr5 Thu Apr 8 10:42:38 2021 -0700 Removing a dupicated word from Code Reveiw, refs #27325 diff --git src/hg/htdocs/FAQ/FAQdownloads.html src/hg/htdocs/FAQ/FAQdownloads.html index c2e92cd..5b5b086 100755 --- src/hg/htdocs/FAQ/FAQdownloads.html +++ src/hg/htdocs/FAQ/FAQdownloads.html @@ -1036,31 +1036,31 @@ as well as functional effect such as intron, coding-synonymous, missense, frameshift, etc.

See our searchable mailing list archives for more information and example queries. We also have information on our blog about Accessing the Genome Browser Programmatically to acquire data.

Why doesn't this SNP have two alleles?

When using the SNP tracks, some records may contain information about one or more alleles instead of -the usual two alleles for the SNP. The following information information should explain how this is +the usual two alleles for the SNP. The following information should explain how this is possible.

One allele (i.e. reference only):
The human genome reference has gone through many different assembly versions. The reference genome has always been a mosaic of sequences from multiple individuals, so it contains some rare or singleton mutations and is not entirely free of errors. Some SNPs were discovered on previous assembly versions, and the latest assembly version has the corrected or common allele, which turns out to be the only observed allele (so the SNP was an artifact of the reference assembly having a rare mutation or error in the past, not a real SNP).
Three alleles:
It's rare, but possible, for the same base to be mutated to different values in different people.
Four alleles: