They look similar because they have both designed for stealth, requiring internal weapons carriage for example. This gives them the bulky fuselage look. Both designs have similar aerodynamic layout, their intakes on the sides, two vertical tails and almost the same wing layout. But they don't have entirely the same design, for example:
the F/A-22 (as it is now designated) has two engines and thus a wider fuselage, also the F/A-22 engine exhaust have thrust vectoring and special exhaust which reduce the heat signature. the special angular exhaust are positioned more inside the fuselage, compared to previous fighters with a similar rear fuselage shape. the F-35 however has a more conventional exhaust, with one big difference, the whole exhaust can be directed downwards (on the B) , so the B variant can vector its main exhaust...this layout was based on the Russian YAK-141 and is for airframe commonality similar to that in the A and C variants.
also the doors required for the SVTOL in the top fuselage, near the canopy, give it that higher spine behind the canopy. The F/A-22 canopy has more of a pop-up position.
then the F/A-22 has a larger airframe, housing more fuel probably, the two engines each about the same as the F-35 single engine.
because the F/A-22 has been designed according to higher specifications in terms of performance (speed, range, systems, agility, max G), it is heavier and also more structural strengthening is needed, in addition to the extra power and fuel.
please take a look at my pages:
http://www.milavia.net/aircraft/f-22/f-22.htmhttp://www.milavia.net/aircraft/f-35/f-35.htmthese probably don't answer your question, but check out the gallery to study the differences yourself, and the links for more info on the designs.