This book is meant to benefit the students of Genetics. An ideal text for the undergraduate and post graduate students of Veterinary Science, Agronomy and general courses of Physiology, Zoology and Botany, this volume contains a separate chapter on twins as material for studying the relative effects of heredity and environment. The chapter on Molecular Genetics has covered Biochemistry and structural formula of DNA and RNA, their biological role, mechanism of transmission of heredity.