49ers roster turnover: Have the cornerbacks improved?

The 49ers rookies report to training camp next week, with the veterans following them five days later. We're continuing our countdown to training camp with a series of articles titled "49ers roster turnover." I'm going through the various position groups and considering how the roster has changed over the last 12 months. We'll take a look at the team's depth chart heading into the first preseason game last year, prior to Week 1 of the regular season, the Super Bowl and then how it currently stands. Four depth charts give us an idea of how the roster developed over the course of the year.

Today we take a look at cornerback. This is a position with three returning starters (we'll count the nickel cornerback role as a starter), but with questions as to how the entire depth chart will shake out by the time Week 1 of the regular season roles around. Here is a look at the how the depth chart has shaken out over the last 12 months.

Preseason 2012 depth chart

CB: Carlos Rogers, Tramaine Brock, Perrish Cox, Curtis Holcomb
CB: Tarell Brown, Chris Culliver, Anthony Mosley, Deante' Purvis
Nickel CB: Carlos Rogers, Perrish Cox

Week 1 depth chart

CB: Carlos Rogers, Perrish Cox, Tramaine Brock
CB: Tarell Brown, Chris Culliver
Nickel CB: Carlos Rogers, Perrish Cox

Super Bowl depth chart

CB: Carlos Rogers, Perrish Cox, Tramaine Brock
CB: Tarell Brown, Chris Culliver
Nickel CB: Carlos Rogers, Perrish Cox

Current depth chart

CB: Carlos Rogers, Chris Culliver, Tramaine Brock, Perrish Cox, Marcus Cooper
CB: Tarell Brown, Nnamdi Asomugha, Lowell Rose, Darryl Morris
Nickel CB: Carlos Rogers, Perrish Cox, Michael Thomas, Darryl Morris

The biggest addition is of course Nnamdi Asomugha. The 49ers also drafted Marcus Cooper in the seventh round, and added a pair of undrafted free agents in Lowell Rose and Darryl Morris. Cooper will get his opportunities in practice and late in preseason games, but at this point Nnamdi Asomugha is the big question. Practices have not had the physicality we will see in training camp, which leaves us to wait and wonder what he has left in the tank. The combination of bump and run coverage and more emphasis on pass rush (and the corresponding blocking) will give us a much better glimpse at what Nnamdi brings to the table.

Perrish Cox returns for his second year, and as I've said before, I think could be one of the more intriguing players to watch in training camp. He was signed last year with no apparent playing time guarantees, and proceeded to move past Tramaine Brock on the depth chart. The question now is how much further he can move up the depth chart. He has a full season under his belt in the system, after sitting out his final year with the Broncos. Could he emerge as a more regular part of the rotation?

And what of Marcus Cooper? Some folks are big fans of his upside, but he faces a tough uphill battle. The 49ers have question marks at cornerback, but the numbers game does not necessarily favor Cooper. Is he a likely practice squad candidate, or could he also climb past Tramaine Brock and earn a roster spot? His best chance at a roster spot will be proving himself on special teams, in order to beat out Tramaine Brock.