
Stephen C. answered 03/18/19
Emmy Winning Composer of Film and Concert Music
Hello, Angel - A basso ostinato is a melody in the bass which is repeated a number of times while music above may be thought of as a series of variations which all work with that same bass part (ostinato).
An ostinato may occur in any part and simply means a repeated melody.
A melodic sequence is different. It can as little as two notes or it can be longer. If take two notes, say C up to G and then follow it with D up to A you have a melodic sequence. If you a melodic figure of C,D,F, followed by D.E.G, followed by E,F.A you have a three note melodic sequence which is implemented three times - each time up a major second.. So, a melodic sequence is a (usually short) melodic phrase which is then repeated at different pitch levels. The rhythms or often the same in the segments of a sequence but sometimes may vary.
Melodic sequences can be used anywhere a composer chooses. They provide a sense of logic and continuity the the music and often occur as a natural part of the flow of creating a melody. If over used they can cause the music to be predictable and obvious.
I hope this is helpful. You ask a follow up question if you like.
Stephen