This textbook has been designed to meet the needs of B.Sc. First Semester students of Zoology. It comprehensively covers two papers, namely Theory paper on Cytology. While this textbook gives a thorough overview of genetics and infectious diseases, it aptly covers important topics such as structure and functions of cell organelles, nucleus, cell cycle, cell division, human chromosomes & its pattern of inheritance. Practical part covering Cell Biology & Cytogenetics Lab has been presented systematically to help students achieve sound conceptual understanding and learn experimental procedures.