Table Of ContentTariq Ahmad Bhat · Aijaz Ahmad Wani
Editors
Chromosome
Structure
and
Aberrations
Chromosome Structure and Aberrations
Tariq Ahmad Bhat • Aijaz Ahmad Wani
Editors
Chromosome Structure
and Aberrations
Editors
Tariq Ahmad Bhat Aijaz Ahmad Wani
Department of Education Department of Botany
Government of Jammu and Kashmir University of Kashmir
Srinagar, India Srinagar, Jammu and Kashmir, India
ISBN 978-81-322-3671-9 ISBN 978-81-322-3673-3 (eBook)
DOI 10.1007/978-81-322-3673-3
Library of Congress Control Number: 2017930685
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Foreword
Chromosomes have always fascinated me as remarkably condensed DNA thread-
like structures regulating all the phenotypic features and physiological processes of
an organism. Equally fascinating is the history of its discovery. Starting right from
1869, when the genetic material was first reported as “nuclein” in pus cells by
Friedrich Miescher, followed by unequivocal experimental evidence provided by
Oswald Avery, Colin MacLeod and Maclyn McCarty in 1944 for DNA as the
genetic material in the cell and then the revolutionary DNA double helical structure
of James Watson and Francis Crick in 1953 based upon X-ray diffraction analysis
done by Rosalind Franklin and Maurice Wilkins – all have proven to be turning
points in our understanding of life processes. The knowledge gained as a result of
global interest in the DNA molecule led us into the era of recombinant DNA tech-
nology, transgenesis, animal cloning and ultimately embarking on Human Genome
Project. The DNA molecule with its fundamental nucleotide base composition has
been the driving force behind all the biological phenomena. The simple organisms
had few base pairs (bp), which continued to grow in number depending upon the
complexity of the organisms along the evolutionary scale. The smallest number of
base pairs (bp) has been reported from a virus – porcine circovirus type with
1.8 × 103 bp. The number of bp continued to increase with the increase in complex-
ity during the course of evolution spanning billions to millions of years. The bacte-
rium Escherichia coli has 4.6 × 106 bp (4288 genes), Caenorhabditis elegans
10 × 107 bp (19,000 genes), Arabidopsis thaliana 15.7 × 107 bp (25,498 genes),
Drosophila melanogaster17.6 × 107 bp (13,600 genes), Mus musculus 6.4 × 109 bp
(20,000 genes) and Homo sapiens 6.9 × 109 bp (30,000 genes). In prokaryotes, the
organisms could manage to accommodate this DNA (chromosome) in their proto-
plasms, but with the evolution of eukaryotes, the increasing size of DNA/chromo-
some ultimately delimited itself from the cytoplasm by nuclear envelope. In order to
accommodate large size of DNA within a limited space, the DNA molecule under-
went process of packaging, for which histone protein and variety of looping, coiling
and coiled coiling helped in condensation of chromosomes. During the course of
evolution, the long DNA broke into smaller pieces, which later became the charac-
teristic karyotype of the organisms. These chromosomes are in their relaxed state
during interphase when the cell is not dividing but are condensed into specific num-
ber and shape of typical metaphase structure during dividing phase. This cycle of
condensation and decondensation is such an organized and orchestrated sequence of
vii
viii Foreword
events that organisms remain healthy and normal, both phenotypically and geno-
typically. Any mishap during interphase and more so during mitotic or meiotic
dividing phases results in genetic abnormalities. There are a variety of genetic syn-
dromes which are the result of accidental changes in the number of chromosomes or
loss or rearrangement of segments of chromosomes particularly during mitotic
metaphase and anaphase and meiotic prophase, which are passed on to the next
generation and become the basis of mild to severe abnormalities and in several cases
become fatal. These biological phenomena prompted the preparation of this book.
The history of development of concept of chromosomal basis of inheritance and
the molecular structure of chromosomes is given in Chap. 3. Chapter 12 encom-
passes the phenomena of number of chromosomes, which is normally fixed for a
particular species, and the consequences of accidental increase or decrease in the
chromosomal number. Chapter 13 describes the abnormalities arising due to struc-
tural rearrangements of chromosomes or chromosomal segments such as inversions,
deletions, translocations, etc., which have far-reaching genetic implications with
physical, physiological and mental debilities. Chapter 6 deals with two more cate-
gories of chromosomal abnormalities, i.e. asynapsis and desynapsis. Conjugation of
the chromosomes during the first meiotic prophase is referred to as synapsis, and the
lack of this pairing is referred to as asynapsis. Desynapsis is the condition when
chromosomes initially pair at pachytene but fail to remain paired at subsequent
meiotic stages. Such conditions usually result in chromosomal imbalance. Usually,
eukaryotic cells are diploid, but there are some eukaryotes that contain more than
two sets of chromosomes. Such cells are called as polyploid and are common in
plants. Rice, for example, are diploid plants, banana is triploid, cotton is tetraploid,
wheat is hexaploid, and sugarcane is octaploid. On the basis of number of chromo-
somes, polyploidy can be divided into euploidy and aneuploidy. Chapter 10 deals
with polyploidy and its role in crop improvement. In addition to normal karyotype,
wild populations of animals, plants and fungi contain B chromosomes, also known
as supernumerary or accessory chromosomes. These chromosomes are not essential
for life. Most of them are entirely or mainly heterochromatic, though some contain
euchromatic segments. These chromosomes have been dealt with in Chap. 2.
Chromosomes can be studied under the light microscope using different types of
chromogenic dyes. Chapter 14 gives a broad outline of all the cytogenetic tech-
niques prevalent for understanding structure of chromosome. Over the past few
decades, versatile methods based on fluorescence in situ hybridization (FISH) have
transformed cytogenetics into a molecular science and provided cytogeneticists
with powerful new tools. FISH procedures are now routinely employed in clinical
cytogenetics. Although chromosomes may appear to be static structures when
viewed under a microscope, cytogeneticists know that chromosomes are actually
dynamic assemblies made up of a DNA-protein complex called chromatin. This
chapter takes stock of all the prevalent techniques, highlighting the principals
involved in each method. Karyotyping, genetic mapping, fluorescence in situ
hybridization (FISH), multiplex FISH, spectral karyotyping, flow cytometry and
microarray have been described. New trends in cytogenetics to understand the
molecular mechanism have been discussed under new generation sequencing.
Foreword ix
Chapter 16 describes the FISH techniques and its applications, while Chap. 4 pro-
vides guidelines to cytological techniques written specifically for the plant chromo-
somes. Chapter 8 describes banding techniques to study different parts of the
chromosomes. The chapter describes G, Q, R banding which requires heating in a
saline buffer prior to staining with Giemsa or quinacrine and is often called T band-
ing, since it also highlights telomeres. C stains heterochromatin in the centromeres,
and NOR silver nitrate stains selectively the satellite stalk of the acrocentric chro-
mosome. Flow cytometry is another cytogenetic technique, which measures optical
and fluorescence characteristics of single chromosome preparation. The informa-
tion obtained is both qualitative and quantitative. The principle involved and its
applications have been discussed in Chap. 5. The 2000s witnessed an explosion of
genome sequencing and mapping in evolutionarily diverse species. While full
genome sequencing of mammals is rapidly progressing, the alignment of whole
chromosomal regions from more than a few species is not possible. Building of
comparative maps for domestic, laboratory and agricultural animals has tradition-
ally been used to understand the underlying basis of disease-related and healthy
phenotypes. These maps also provide an opportunity to use multispecies analysis as
a tool to infer karyotype evolution. A record of the history of karyotype changes that
have occurred during evolution has been attained comparative chromosome maps.
Chapter 9 deals with karyotype evolution and its applications.
Cytomixis is an interesting phenomenon which involves migration of chromo-
somes from one plant cell to another through intercellular cytomictic channels. It is
most frequently detectable in microsporogenesis in plants and spermatogenesis in
animals. Chapter 10 deals with this phenomenon and its biological and genetic
implications.
Two special topics have been discussed in Chaps. 7 and 11. Chapter 7 deals with
cytogenetic studies on an Indian hyacinth Drimia Jacq. This herb has medicinal
importance. Chapter 11 is about mutagenesis in one of the major pulses of India,
Vicia faba. Mutagenesis is the most important method of inducing alteration by
mutagens in a genotype to enlarge the variability of quantitative characters such as
days to flowering, number of flowers per plant days to maturity, plant height, num-
ber of fertile branches per plant, number of pods per plant, number of seeds per pod,
mean pod length, mean pod girth, seed weight, etc. in the shortest possible time. The
authors found that induction of meiotic aberrations was higher in combined muta-
gen treatments, which is more effective in inducing additional variability than indi-
vidual doses in Vicia faba L. var. minor and major.
I only hope that readers will enjoy going through different aspects of chromo-
somal structure and their aberrations, with consequential phenotypic and genotypic
deviations.
Lahore, Pakistan Abdul Rauf Shakoori
March 7, 2016
Preface
The authors take great pleasure in presenting the readers this enlarged and extensive
book on chromosome with special emphasis on its structure, techniques and aberra-
tions. The book is a valuable asset to all the stakeholders at undergraduation and
postgraduation level, particularly students, teachers and researchers.
During the last few decades, there has been remarkable progress in research on
various aspects of chromosome including plant and animal systems. Geneticists,
evolutionary biologists, ecologists, etc. have been exploiting the various aspects of
chromosomal research to understand the genetic architecture of organisms, prepare
chromosome linkage maps, understand evolutionary relationship among organisms
and groups of organisms and understand speciation, adaptation and modes of inva-
sion of plant and animal species. The structural organization of chromosome has
been greatly understood enabling the identification of gene sequences and mapping
of gene loci and their regulatory aspects. The manipulation and engineering of chro-
mosomes have facilitated their transfer across kingdoms for genetic improvement of
crop and animal species. The present book is intended to fulfil the needs of students,
teachers, researchers and all stakeholders who are engaged in the study of evolution,
biodiversity, mutation breeding, plant breeding, chromosome manipulation and
genetic and physical mapping. The book comprises of 16 chapters. Beginning with
the introduction of chromosome and organization of genetic material, these first two
chapters provide a deep insight into the different aspects of chromosome with
detailed information and some more emphasis on organization of eukaryotic chro-
mosomes. This is followed by chapters on B chromosome and high-throughput ana-
lytical techniques like chromosome banding, FISH, GISH, flow cytometry, etc. to
give the reader an easy understanding of these techniques and their applications in
chromosomal studies. This is followed by a series of chapters on induced chromo-
somal aberrations, asynapsis and desynapsis, cytomixis and structural and numeri-
cal aberrations with special reference to plant and animal chromosomes. The
chapters on cytogenetic studies of Indian Drimia Jacq. (Urgineoideae:
Hyacinthaceae), karyotype evolution and its utility and polyploidy provide valuable
information. The possible mechanisms and their consequences and possible role in
genetic analysis are emphasized in these chapters. The chapters of the book are
from eminent authors and researchers of the world scientific community who are
working on different aspects of chromosome research.
xi
xii Preface
In presenting this book, we wish to express our gratitude to Prof. A.H. Khan and
Prof. M. Anis of the Department of Botany, Aligarh Muslim University, Aligarh.
Without whose help and encouragement, we would have never become the students
of cytogenetics. We are thankful to the authors who contributed chapters for this
book which is the outcome of their decades of research work. Our thanks especially
go to Prof. Abdul Rauf Shakoori, distinguished national professor and director and
professor emeritus, for his significant contribution in the form of well-oriented and
innovative chapters for this book. Many of the ideas in the book are the outcome of
teacher training programmes, conferences, workshops and seminars. We wish to
express our gratefulness to all teachers and researchers associated with these pro-
grammes for their suggestions and advice without holding them responsible for any
shortcoming in the book.
We are also grateful to our students whom we taught all these years, because it is
through teaching them in the classroom that we learnt much of cytogenetics we
know.
We are also thankful to Manjusha Nalamolu, PI of the book, for her whole-
hearted cooperation and sympathetic assistance whenever we required. We are also
thankful to Springer for publishing our book.
In the end, we wish to acknowledge our debt to our family whom we left waiting
on several evenings, while we were busy in finalizing the manuscript or the illustra-
tions for this book.
Srinagar, India Tariq Ahmad Bhat
Srinagar, Jammu and Kashmir, India Aijaz Ahmad Wani
