In population genetics, Haplogroup K(xLT) is a human Y-DNA Haplogroup (formerly MNOPS). A haplogroup (from the Greek: ἁπλούς, haploûs, "onefold, single, simple") is a group of similar haplotypes that share a common ancestor having the same single nucleotide polymorphism (SNP) mutation in all haplotypes. Haplogroup K(xLT) shares a common ancestor with Paragroup K* and Haplogroup LT, and together they form a macrohaplogroup called Haplogroup K.
Haplogroup K(xLT) is the ancestral haplogroup to haplogroups K1, K2, K3, K4, M, NO, P (which contains haplogroups Q and R), and S.
The naming of K(xLT) was a "revolution" in haplogroup designation, because prior to that the formula "K(xLT)" never designated a single haplogroup, but instead "everything that belongs to K, but does not belong to LT". The traditional way would have been to rename haplogroups K1, K2, K3 and K4 into U, V, W and X, and to rename MNOPS into MNOPSUVWX, but the YCC decided otherwise. This poses a great problem, because there is no way to disambiguate between "K(xLT)" in the traditional and in the new meaning. It also creates a confusion whence haplogroups K1, K2, K3, K4 do not belong directly to haplogroup K, but instead to haplogroup K(xLT).