In genetic nomenclature, the ">" is used to signify which allele is the ancestral (original) or "wild type" allele and which allele is the SNP (change present in 1%+ of the population) or "variant" allele. The ancestral allele is to the left of the ">" and the SNP allele is on the right.
In the example of MTHFR 677 C>T, C is the ancestral/wild type allele and the T allele is the SNP/variant allele.
