There will undoubtedly be movement between the two squads
England coach Stuart Lancaster has included uncapped pair Calum Clark and Billy Twelvetrees in his 33-man squad for the Six Nations.
Northampton forward Clark returns to the England fold after serving a 32-week ban for breaking an opponent's elbow last year.
Joe Launchbury, Tom Youngs, Mako Vunipola and Freddie Burns have also been promoted to the senior squad after making an impact in England's end-of-year internationals.
Lancaster, who also announced a 32-man squad for the second-string Saxons team, said: "The fact that we have spent significant time deliberating over quite a few players shows how tough the competition is to get into this 65 and the strength in depth that is emerging.
"We have made some changes to both squads and we feel that reflects the players' form during the first half of the season.
"There will undoubtedly be movement between the two squads as we go through the Six Nations and that was evident in the year-end Internationals, with players in form pushing through such as Freddie Burns, Joe Launchbury, Tom Youngs and Mako Vunipola."
James Haskell of Wasps has replaced Phil Dowson in the back row, while Saracens wing David Strettle comes in for Charlie Sharple.
Launchbury takes the place of Wasps colleague Tom Palmer, with Youngs coming in for injured Bath hooker Rob Webber.
At centre, Lancaster has dropped Anthony Allen and Jordan Turner-Hall for Twelvetrees and his Gloucester teammate Burns.
Clark was selected for last season's Six Nations campaign but he was then sidelined for over eight months after admitting in March to breaking Leicester hooker Rob Hawkins' elbow in the Anglo-Welsh Cup final.
Twelvetrees, meanwhile, has impressed in his first season at Gloucester alongside Burns, who made an eye-catching debut in the 38-21 triumph against New Zealand at Twickenham in the end-of-year internationals.
Burns, Launchbury, Vunipola and Youngs were all classed as injury replacements when they played during that series, but they have now been formally selected.
England begin their Six Nations campaign at home to Scotland on February 2.
England squad: Calum Clark, Alex Corbisiero, Dan Cole, Tom Croft, Dylan Hartley, James Haskell, Tom Johnson, Joe Launchbury, Courtney Lawes, Joe Marler, Ben Morgan, Geoff Parling, Chris Robshaw, Mako Vunipola, Thomas Waldrom, David Wilson, Tom Wood, Tom Youngs, Chris Ashton, Brad Barritt, Mike Brown, Freddie Burns, Danny Care, Lee Dickson, Owen Farrell, Toby Flood, Ben Foden, Alex Goode, Jonathan Joseph, David Strettle, Manusamoa Tuilagi, Billy Twelvetrees, Ben Youngs.
England Saxons squad: Mouritz Botha, Nathan Catt, Louis Deacon, Paul Doran Jones, Phil Dowson, Will Fraser, Joe Gray, Graham Kitchener, Shaun Knight, Matt Kvesic, Matt Mullan, David Paice, Tom Palmer, George Robson, Ed Slater, Henry Thomas, Billy Vunipola,
Nick Abendanon, Anthony Allen, Tom Biggs, Elliot Daly, Kyle Eastmond, George Ford, George Lowe, Jonny May, Ugo Monye, Joe Simpson, Charlie Sharples, Joel Tomkins, Jordan Turner-Hall, Christian Wade, Richard Wigglesworth.