The child is (according to psychodynamic theory) identifying with the opposite parent, to the fact that they are attracted to them. A lot of parents (just for example) will have "Daddy's Little Girl" or "Mom's Little Boy".

The male child, in this theory, is supposed to be afraid that the father will want (in case of the boy) to cut off their penis because they are (in their mind) competition for the mother, whom they consider their first love interest.

According to Freud, anyhoo.

With the Electra complex, it is in reverse. The girl loves her father, and worries about her mother hating her. Freud talks in very simplistic (and stupid for Freud) terms about girls wanting to have a penis, and that since they dont, they feel the attraction to their father.

Here are the two links for Oedipus and Electra in Wikipedia for your perusal... Oedipus
Electra

Hope this helps...