If you believe that learning about pedigrees means anything, but you have no idea how to begin, here are a few ideas. There may well be better ideas, but assuming that some start is better than no start, and assuming that the thoroughbred is the key breed underlying most others, then let`s start there.
In 1935, Nearco was foaled in Italy, by Pharos x Nogara, bred by Federico Tesio. He`s a good starting point, because he`s relatively “modern”, and because, through the influence of three of his sons, he is in the pedigrees of almost all modern thoroughbreds and Tb crosses. The three sons, all of whom created their own dynasties, were Nasrullah (1940), Nearctic (1954), and Royal Charger (1942)
Nasrullah sired Bold Ruler, sire of Secretariat. He sired Nashua, maternal grandsire of Mr. Prospector. He sired Never Bend, grandsire of the two top Australian gold medal team eventers at the 1996 Atlanta Olympics. Google Nasrullah, and learn about him, because he`s in the pedigrees of hundreds of eventers, hunters, jumpers, all over the world. He was a brilliant racehorse, but he was considered tough, stubborn and obstinate. I was at a Montana ranch 30 years ago, and the old guy who owned the ranch said that he loved Nasrullah horses for ranch work, because once you got that tough streak working for you, instead of against you, they would work til they dropped.
So start with Nearco and Nasrulla in your quest to learn about pedigrees.
How Good Riders Get Good 
What I learned is that Secretariat had triple sized heart compared to average horse. This is genetic mutation passed only through female chromosome. So if I were to get Secretariat’s baby I would be getting one of dam sides of his line 🙂