2. Contents
Cytogenetic studies and polymorphic variants;
Spectral karyotyping; Flow cytometry;
Chromosomal phylogeny; Chromosomal banding techniques;
Methods for detection of structural chromosomal aberrations;
Cytogenetic analysis of primary cultures and cell lines; In Situ hybridization.
3. Introduction
• Cytology is a branch of biology that deals with the study of cells, chromosomes,
and other cell organelles including their structure, function, and formation. Robert
• Hooke (1635–1703) coined the term cell in 1665 after observing a piece of cork
under a microscope.
• Antoni van Leeuwenhoek wrote a letter on June 12, 1716, in which he described
his discoveries such as bacteria, free-living and parasitic microscopic protists,
sperm cells, blood cells, and microscopic nematodes and rotifers
• Robert Brown (December 21, 1773–June 10, 1858), a botanist and paleo botanist,
described a cell nucleus and cytoplasmic streaming. Also gave concept of
Brownian motion
5. Continued….
• Matthias Jakob Schleiden examined plant structure and Theodor Schwann
inspected animal tissues under the microscope and recognized the importance of
cell nucleus and developed the cell theory.
• Rudolf Ludwig Carl Virchow was known as “the father of modern pathology
because he linked the origin of cancer cells from normal cells.
• Eduard Adolf Strasburger was the first to describe accurately the embryo sac in
gymnosperms (conifers) and angiosperms (flowering plants), and double
fertilization in angiosperms. He gave modern law of cytology “New cell nuclei
can arise from the division from other nuclei”.
• August Friedrich Leopold Weismann developed germ plasm theory (i.e., that
inheritance only takes place by means of the germ cells or the gametes).
6. Continued….
• von Waldeyer-Hartz , a German anatomist, coined the term chromosome (meaning
coloured bodies) in 1888.
• Chromatin, mitosis, meiosis were defined later on.
• After Mendel,s lawas, significant progress was made, cytoplasmic basis of
Mendelian Phenomena were reported and chromosomal theory of inheritance was
proposed by Sutton and Boveri.
• Techniques like “Camera Lucia” were developed afterwards for sketching cells
and chromosomes.
• Smear (for human chromosomes) and squash (mitotic and meiotic plant
chromosomes) techniques are now used.
• Techniques further differ according to chromosome number and genome size.
7. Continued….
• For example, ice-cold water pretreatment, acetic alcohol fixation (1:3), and
acetocarmine/Feulgen staining produce good quality chromosome spreads for
cereal (barley, wheat and rye, and oat) chromosomes.
• For soybean chromosomes pretreatment with 8-hydroxyquinoline at 13°C for 2–3
h, fixation in acetic alcohol(1:3) and Feulgen staining works the best for the
soybean chromosomes
• Since 1970, chromosome banding techniques, fluorescence in situ hybridization
(FISH), genomic in situ hybridization, fiber FISH, flow karyotyping by flow
cytometry, and chromosome image analysis are being used in plants.
8. Continued….
Cytology includes
• handling of mitotic and meiotic chromosomes (pretreatment of tissues such as
roots, fixation of roots and flower buds, and staining of roots and anthers)
• function and movement of chromosomes (mitosis and meiosis),
• determination of the number and structure of chromosomes, and karyotype
analysis.
The study of cytology is the foundation of genetics, and the combination of both,
termed;
cytogenetics, give us a clear understanding of heredity, biosystematics,
chromosomal aberrations, and the association of a gene with a particular
chromosome using primary trisomics, genome analysis, and wide hybridization.
9. Continued….
• Chromosome cytology progressed rapidly in maize, Datura, faba bean, tomato,
wheat, barley, and other plants.
• Many advances in cytological techniques using many important crops have been
reported primarily in research papers.
10. Polymorphic variants
• Polymorphism, as related to genomics, refers to the presence of two or more variant forms of a
specific DNA sequence that can occur among different individuals or populations. The most
common type of polymorphism involves variation at a single nucleotide (also called a single-
nucleotide polymorphism, or SNP)
• Variant: a site where the genome you are looking at differs from a reference genome of that
species.
• SNP: a single nucleotide variant often, but not always, in a position of the genome where a
significant proportion of the species' individuals show variation.
Various types of polymorphisms include:
• single nucleotide polymorphisms (SNPs)
• small-scale insertions/deletions.
• polymorphic repetitive elements.
• microsatellite variation.
11. Karyotype Analysis
• Karyotype is the number, size, and morphology of the chromosome set of a cell in
an individual or species (Battaglia 1994).
• Karyogram is the physical measurement of the chromosomes from a
photomicrograph where chromosomes are arranged in descending order (longest
to shortest).
• An idiogram represents a diagrammatic sketch (interpretive drawing) of the
karyogram
