**Meet the editor**

Professor Padma Tirunilai has been actively engaged in teaching and research in the field of Human and Medical genetics over four decades. Her master's and doctoral degrees in Genetics are conferred by Osmania University, India. She served the university in various academic and administrative capacities and also The Indian Society of Human Genetics as life member and

secretary. She conducted several research projects, workshops and was mentor of students working for Ph.D. degree in Human Genetics. Her academic contributions are related to gene mapping and genetic analysis of Mendelian and complex disorders like Cataracts, Essential hypertension, Lipidemias, Hearing Impairment, Glaucoma and Epilepsy. She has authored reviews and chapters for books and articles that were published in several reputed journals.

## Contents

## **Preface XI**


## Preface

Cytogenetics - the study of chromosomes as hereditary units has been an active field of research for over a century, contributing to the understanding of organization of chromosomes, of genetic and non-genetic components they are comprised of and knowing ultimately the entire organization of genome of a given species. At the turn of the last century, the merger of the two fields - cytology describing the cell structure, function and division and genetics that governs the inheritance of traits through generations, resulted as a new field "Cytogenetics" that has progressed tremendously with an outcome of multiple applications like identification of a species and its evolution based on the chromosome number, their structural and numerical variations; role of chromosomal aberrations in the etiology of birth defects, syndromes and malignant tissues. To-day clinical evaluation of several conditions and their therapeutic interventions are based on detailed cytogenetic analysis carried out at micro level using advanced technologies that came into vogue with the passing time. The first foundation to this very important field of clinical cytogenetics was laid in the year 1956 when Tjio and Levan established the chromosome number in humans as 46 ruling out the much believed number of 48 that was also found in great apes. The number was interpreted to have reduced to 46 because of the formation of chromosome 2 due to merger with ancestral chromosome. The preparation of human karyotype for the first time in 1959 led to the identification of numerical aberrations in the following years associated with Down's, Turner and Klinefelter syndromes which implied the need for routine screening for chromosomal anomalies in certain clinical conditions. At the same time structural defects like deletion of chromosome 21 referred as Philadelphia chromosome that was found consistently in patients of chronic myelogenous leukemia opened up new approach of screening for chromosomal variations such as deletions, duplications and translocations in patients with different types of tumors. Further development of banding techniques and study of prometaphase chromosomes facilitated better identification of these variations with high resolution. Culturing of free amniocytes was another breakthrough that allowed the identification of chromosomal abnormalities associated with birth defects. These classical cytogenetic techniques became mandatory for several clinical conditions and were adopted by many laboratories as a routine. Later with the adoption of molecular biology techniques especially the hybridisation technique, the field of cytogenetics transformed itself into the field of "molecular cytogenetics". Discovery of DNA probes and their tagging with fluorescent dyes evolved a new technique called "Fluoroscent labeled in situ Hybridisation" (FISH) that enables chromosomal analysis at various levels including direct allocation of DNA regions to specific chromosomal sites, detection of gain or loss of interstitial chromosomal regions such as microdeletions, duplications and several structural variations that cannot be traced by the application of age old classical techniques. Other significant contributions of FISH include study of interphase nuclei, cultured specimens and cells from specimens embeded in paraffin. In spite of these advancements, heterogeneous chromosomal changes occurring in cancer cells make the interpretation of the observations more complicated and challenging. Thus the determination of overall genomic changes occurring in a given tissue affected with cancer growth became the need of the hour. As a consequence two types of "Comparative genomic hybridisation" (CGH) techniques referred as metaphase CGH and array based CGH emerged enabling the identification of "Copy number variations" (CNV) in the genome with cells showing abnormal number of copies of DNA sections i.e either deletions or duplications. These CNVs may show association with certain clinical conditions and help in predicting risk and also diagnosis. All these approaches have their merits and demerits and in general are tedious, time consuming and need manpower with stringent handling. This naturally prompted the development of several automated methods for culturing cells in mass scale, use of membrane bioreactors, and image analysis for interpreting the cytogenetic observations made. It has now become imminent to screen and detect abnormalities with optimal precision to aid the therapeutic interventions and treatment of clinical conditions especially the malignant tumors. The technologies that are expensive now are expected to become more cost effective and affordable in due course.

This book covers various aspects related to recent trends in cytogenetics with minute details of methodologies that can be adopted in clinical laboratories. The focus is on the basic methods of primary cultures, cell lines and their applications; microtechnologies and automations; array CGH for the diagnosis of fetal conditions; various cytogenetic approaches to deal with acute lymphoblastic and myeloblastic leukemias in patients and survivors of atomic bomb exposure. Use of digital image technology in analyzing cytogenetic changes is emphasized taking sting less bees from Brazil as a model organism. Use of chromosomes as tools to discover biodiversity is also discussed quoting the example of Erythrinidae fish family. While concentrating on the advanced methodologies in cytogenetic studies along with their applications, the authors have pointed out the need to develop the cytogenetic labs with modern tools and approaches to make precise and effective decisions to benefit the patient population.

> **Dr. Padma Tirunilai**  Retd. Professor, Department of Genetics, Osmania Univertsity, Hyderabad India
