Apprentice

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The Apprentice is a birthsign that confers a 100-point bonus to a player's Magicka attribute, but also gives a 100% Weakness to Magic. Spellcaster essential; aggressive.

(Summary and picture from Official Elder Scrolls Site)

[edit] Usefulness

The apprentice works nicely with Bretons since the Bretons' magical resistance helps to offset the magical weakness of this Birthsign. Sneaky characters that want a high magicka pool do well with this birthsign because Silence poisons and spells usually stop you from receiving magical damage from spellcasters. Altmer with this sign have very high magicka, but are extremely vulnerable to magic attacks.

[edit] Stone

Located South of Skingrad, there's an Apprentice Stone that you can touch to receive the Void Seed Greater Power. Almost due south of Grateful Pass Stables, before the river/chasm.