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"?