DNA replication isn’t perfect, and some letters will get replaced by other letters in the copies inherited from parents to their children, producing new unique strings of letters, that can be associated to a specific individual. Then, when this individual reproduces, she/he inherits this unique sequences to her/his children, which can be identified as descendants from this individual. Due to this process, we can identify the unique DNA sequences that are shared among a population, and make approximations about how long ago their common ancestors were alive.
The approximately 3,234 letters inherited by each parent to their children are made by randomly taking DNA sequences from the 6,468 total letters in each of the 2 parents, resulting in new unique copies inherited to each children, with each copy as a mosaic made from half the genetic material of each parent. So, we didn’t inherit neither of the copies passed from our grandmothers and grandfathers to our parents, but a mix of these copies into new ones. That’s why brothers and sisters can be very similar or different. Because those who are similar are likely to have inherited similar mixes from the genetic material of their parents, and those who are different, are likely to have inherited less similar mixes. Plus, the creation of new sequences in the replication errors mentioned before.
All this processes make each one of us a really complex mosaic of DNA sequences, mixed each generation, which result in difficult analysis to reconstruct our past. Fortunately, this can be simplified by focusing in some special DNA sequences, which are not as affected by this mixing process. This special DNA sequences are present in DNA packages that don’t follow this mixing process and then the package inherited from the parents would be almost identical to the copies inherited from the grandparents. This two DNA packages are the Y-chromosome which is inherited from every father to his sons, and the Mitochondrial-chromosome, which is inherited from each mother to her daughters and sons. The Y-chromosome contains approximately 58 million letters, while the Mitochondrial-chromosome contains approximately 16,569 letters, making the Y-chromosome much more informative, although with the disadvantage of being present only in men.
Still, those special DNA packets are a good way to infer ancestry, and therefore to take a little look into our pasts and origins, tracing back some of the expeditions our ancestors went through, or even better understand our biology, and how to avoid or cure diseases.
1. Dravidian (H-L901/M2939) 25-45 kyBP
2. Austronesian K*(M9), LT(L298/P326) 41-49 kyBP, M(P256) 32-47 kyBP, S (M230) 28-41 kyBP
3. Sino-Nordic (East Asia, China, North Eurasia ) (NO/N-O) 30-40 kyBP
4. Amerindian (Q-M242) 19-27 kyBP
5. Indo-European (R-M207) 17-32 kyBP
Haplomap F https://haplomaps.com/haplogroup-f/
P.S. Modern Europians are mostly descendents of Amerindian branch R1 , Mesopotamian