Question: Do zombie villagers in the Xbox 360 edition spawn randomly or does there have to be villagers in the world originally

Answer: 
As of [TU14](http://minecraft.gamepedia.com/Xbox_360_Edition_version_history#xbox-TU14), Zombie Villagers are part of console edition.

[From the wiki](http://minecraft.gamepedia.com/Zombie_villager#Variants):

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> Zombie villagers comprise 5% of all spawned zombies. They behave as ordinary zombies, but their character model's head and face is reminiscent of that of a villager, shaded with a darker green hue.
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> Zombie villagers can also result from zombie attacks on villagers. If any type of zombie kills a villager, there is a chance that the villager will transform into a zombie villager (100% on hard difficulty, 50% on normal, 0% on easy).
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Zombie villagers will spawn in worlds where there are no villagers.
A few months ago, Zombie Testificates were added in an update to the XBox 360 (I don't have it for PC, so I was super psyched when I first saw this).