No group of racehorses goes under a stronger microscope than the field for the Kentucky Derby. But even under the heaviest scrutiny, many things remain unknown about the entries until they cross the finish line.

One of the biggest variables that can only be forecasted at this point is the ability to handle the Derby’s 1 1/4-mile distance. It’s a distance no horse in the field has faced, and one that many in the field will never see again in competition.

One of the pleasant surprises of this year’s Kentucky Derby and Oaks trails has been the rapid ascension of Take Charge Indy, who is positioned to have starters in both races from his first crop.

Despite finishing outside the top 10 by first-crop average yearling sale price with his debut foals and being sold to stand in Korea before that group hit the track, Take Charge Indy sits atop the North American second-crop sire standings by winners, stakes winners, and earnings as the calendar rolls into Triple Crown season.

The American equine conquest of Europe that began with Sir Ivor’s victories in the 1968 2000 Guineas and Epsom Derby revolutionized the international breeding industry. The American Thoroughbred, after decades of crossing the tough, sound racemares required by American dirt tracks with more refined, European stallions had reached a pinnacle heretofore unseen that resulted in the 1970's onslaught of Secretariat, Ruffian, Seattle Slew, Affirmed, Alydar, and Spectacular Bid.

Spendthrift Farm in Lexington, Ky., will stand Grade 1 winner and Kentucky Derby hopeful Free Drop Billy upon his retirement from racing.

Free Drop Billy, a 3-year-old son of Union Rags, has won two of eight starts and has earnings of $625,220. He won on debut as a 2-year-old by three lengths, then finished second in the Grade 3 Sanford Stakes and the Grade 1 Hopeful Stakes at Saratoga before winning the Grade 1 Breeders’ Futurity at Keeneland.

The apple often doesn’t fall far from the tree, but it did with Flameaway. Trainer Mark Casse said that despite having some famously high-strung relatives, Flameaway is a laid-back horse whom he feels confident about leading through the Kentucky Derby hoopla.

Flameaway’s broodmare sire is 2000 Derby winner Fusaichi Pegasus, whose antics were notorious, and his sire is Scat Daddy, whose offspring “can get a little excited sometimes, too,” Casse said.

Unbeaten Arkansas Derby winner Magnum Moon will be chasing the ghost of Apollo on Saturday evening – and also chasing a double for sire Malibu Moon.

Of the 14 stallions likely to be represented by Kentucky Derby starters, only Malibu Moon has sired a Derby winner. That was Orb in 2013.

Justify and Vino Rosso will stand in the Kentucky Derby starting gate together Saturday afternoon, but it won’t be the first time the two chestnuts have been in close proximity. The colts were born just one day apart at John Gunther and daughter Tanya Gunther’s Glennwood Farm, which raised them and sold them days apart as yearlings.

But the Gunthers could be forgiven if their attention is divided between Kentucky and England on Saturday, because Glennwood homebred Without Parole could also chase classic glory this weekend in the English 2000 Guineas at Newmarket.

Kentucky Derby contender Bolt d’Oro is named for world-record-setting sprinter Usain Bolt, who was adding to his gold-medal tally at the 2016 Rio Olympics the month the colt was purchased by owner and trainer Mick Ruis at Saratoga.

The fingerprints of Gainesway’s past and present can be found all over this year’s Kentucky Oaks.

Nowhere are they imprinted deeper than with Ashland Stakes runner-up Eskimo Kisses, who is co-campaigned as a homebred by Gainesway, the Lexington, Ky., operation of Antony Beck. Eskimo Kisses will attempt to emulate the success of another prominent Gainesway resident who won a big race at Churchill Downs in early May, her granddam Winning Colors, who triumphed in the 1988 Kentucky Derby.

The Kentucky Derby is not only a test of speed and stamina – it is a test of mental fortitude for a young horse, with the pressure cooker culminating in the “wall of sound” as the field turns for home in front of more than 160,000 at Churchill Downs. Mendelssohn has shown the speed and stamina, and his breeders think he has the mental fortitude to handle the stress of the May 5 Derby.