CBSE Class 12 NCERT Book for the Chapter-5, Principles of Inheritance and Variation. NCERT Books are more than enough for you to cover the entire CBSE syllabus. You need to clarify your concepts that are given in the NCERT books.
Many times CBSE will ask twisted questions in the board papers. The students who simply mugged up NCERT books will think that the paper was out of these books. However, one needs to understand that by studying NCERT books, CBSE means that you should clarify your concepts and learn how to apply them.