The 2015 Kentucky Derby: Fathers and Sons

Of the 20 horses now expected to line up in the starting gate in Saturday's Kentucky Derby (G1), 10 -- exactly half -- were sired by veterans of Derbies past.

Three are by Kentucky Derby-winning stallions. Dortmund is by Big Brown, the 2008 winner, and like his sire, he enters the Run for the Roses unbeaten. Ocho Ocho Ocho is by 2007 victor Street Sense, and International Star is by 2000 hero Fusaichi Pegasus.

Over the course of Derby history, 12 Derby winners have gone on to sire Derby winners. The most recent was Unbridled (1990), responsible for Grindstone (1996).

Likely favorite American Pharoah, a great-grandson of Unbridled, represents the fourth straight generation in his male line to make a Derby appearance. His sire and paternal grandsire, Pioneerof the Nile and Empire Maker, were each runner-up in their respective years (2009 and 2003). Empire Maker is a son of Unbridled.

Materiality and Keen Ice are both by Derby third-place finishers who went on to reign as the best of their crops. Materiality is by Afleet Alex, the champion three-year-old colt of 2005, while Keen Ice is by eventual two-time Horse of the Year Curlin (2007-08).

Frosted, Firing Line and El Kabeir are the third consecutive generation of Derby runners in their male lines.

Frosted is by Tapit (ninth in 2004), who is in turn by Pulpit (fourth in 1997). If Pulpit's sire, A.P. Indy, hadn't been scratched due to a bruised foot on the morning of the 1992 Derby, Frosted would be a fifth-generation Derby contestant. A.P. Indy is by 1977 Triple Crown legend Seattle Slew.

Firing Line is by Line of David (18th in 2010), a son of Lion Heart, the runner-up in 2004. El Kabeir is by Scat Daddy (18th in 2007), who is by Johannesburg (eighth in 2002).

Rounding out the progeny of Derby runners, Itsaknockout is by Lemon Drop Kid (ninth in 1999), who later captured the Belmont S. (G1) and ranked as the champion older male of 2000.

Photo: Big Brown (credit Charles Pravata/Horsephotos.com)