The Wall Street Journal ran an interesting article the day before this year's Kentucky Derby was run:
Racing's Royal Bloodline: Most racehorses today descend from a stallion named Native Dancer. Has the sport become too reliant on one set of genes?

Interesting stuff about breeding and genetics--things we've touched upon on this board in regards to dogs, etc.

The WSJ article begins as follows:

"No matter what happens in tomorrow's Kentucky Derby, one outcome is guaranteed. The winning horse will be related to Native Dancer.  All 20 horses in this year's race are descendants of this massive thoroughbred, who died in 1967."