transmitted and untransmitted alleles

Question

[yh362]

Sorry the question seems very basic, yet I coulnd't find it on google. When browsing through the HapMap3 project release, I see

• Files are organised in a snps x haplotypes format, so every row represents a SNP and every column a haplotype.

          - The first row (header row) contains the IIDs of the individuals that have been phased.
            Suffixes _A and _B represent **transmitted and untransmitted alleles**, respectively,for a 
          particular genotype.
            For instance, NA19009_A would be the transmitted allele of genotype NA19009 at that site.
  

  What's the definition of "transmitted and untransmitted alleles"?

Answer 1

[Kevin Blighe]

The terms 'transmitted' and 'un-transmitted' allele are typically heard in the realm of family-based genetic studies, such as in the family transmission disequilibrium test (family TDT). Basically, the transmitted allele is the one that is passed to offspring, e.g., from an affected mother to an affected son, while the un-transmitted allele is not passed and is thus 'lost' in that particular lineage.

For example:

• Mom's genotype for SNP4: C|G
• Son's genotype for SNP4: C|A

C is the transmitted allele; G is the un-transmitted allele.

Kevin