Mitochondrial DNA suggests that nearly all modern-day dogs slide into one of four monophyletic haplogroups which can be named haplogroups A, B, C, and D. Nearly all of dogs slide in haplogroup A. The mDNA "molecular clock" signifies that 22,800 YBP the very first genetic divergence (split) happened in haplogroup A, causing the lineages A1b and A2.