Cytogenetic method

CYTOGENETICS
Cytogenetics = The study of chromosome
number, structure, function, and behavior in
relation to gene inheritance, organization and
expression

CHROMOSOME
Chromosome
Chromo = colored in
response to dye
Some = body
Chromosome of Eukaryotes have been the traditional subject for cytogenetic
analysis because they are large enough to be examined with light
microscope

Why Analyse Chromosomes and Genes?
Genetic errors arise from deletions or insertionsof genetic material, abnormal numbers of whole chromosomes or genes, and even from misplacement of a single base in the DNA sequence.
Genetic abnormalities can range from relatively harmless to severe: from vitamin deficiencie and food allergies to cancer, birth defects and infant mortality.

Cytogenetic methods to detect chromosomal
abnormalities underlying human birth defects usually
involve analysis of mitotic chromosome

What tissues are appropriate for chromosome study?
• A tissue that can be stimulated to undergo cell division in-
vitro
• It is only during mitosis of the cell cycle that distinct
chromosomes can be visualized with a light microscope
After culturing, in-vitro, a proportion of
cells are arrested in mitosis, and are then “harvested” for
chromosome analysis After harvesting, the cell
preparations are dropped onto glass slides and stained. For
most chromosome analyses, a G-banding technique is
utilized for staining.
Metaphase spread

The chromosomes are so named as they may
be stained by certain dyes
Chromosomes are composed of chromatin,
which is composed of protein and DNA
When cells are not dividing, the genetic material
is decondensed
Chromosomes become visible as distinct
structures when the cell divides
.

Chromosome
.

.
Chromosomes of different species differ
in number and information content
Humans and several other species of
organisms have 46 chromosomes

Karyotyping
Karyotype
A pictorial display of metaphase
chromosomes from a mitotic cell
Homologous chromosomes- pairs
Karyotyping
Karyotyping is the analysis of
chromosomes
Cytogenetics is the study of
chromosomes and inheritance
Cytogenetics is based on studies of
humans as well as Drosophila and other
organisms

Preparing a karyotype
Harvested cells are first cltured
The cells are then treated with colchicine which arrests the cells in metaphase, and then treated and stained to observe the chromosomes
Chromosomes can be photographed or visualizedd using a computer, and then analyzed
Chromosomes are identified by size, position of the centromere, and banding and staining regionss

The analysis involves comparing chromosomes for their length, the
placement of centromeres (areas where the two chromatids are
joined), and the location and sizes of G-bands.
.

METAPHASE CHROMOSOMES

KARYOTYPED CHROMOSOMES

G – BANDED CHROMOSOMES

Banding patterns on human mitotic chomosomes
due to regions of condensed chomatin (darker - G
bands) and less condensed chromatin (lighter - R bands)
.

Human chromosome number is determined by their
length in “mitotic figures"
.

International System for Cytogenetic
Nomenclature, (ISCN,1995)
Short arm of the chromosome = p
Long arm of the chromosome = q
Bands are numbered independently
on the short and long arms
Centromeres = p10,q10
Band numbers increase as move from
the centromere to the telomere
.

Hundreds of genes are encompassed
within a single G-band.
Therefore, most constitutional chromosome
abnormalities are associated with multiple
congenital anomalies.
Therefore, deletion of a single gene cannot be
detected by G-banding.
.

Conclusion
The evolution of cytogenetic techniques and
the mapping of the human genome have
provided scientists with a great deal of
insight into the causes of numerous genetic
disorders. Though rooted in early
chromosome staining and gene mapping
techniques, modern FISH, SKY, and CGH
methods have far outshone their
predecessors by providing an unprecedented
view of human chromosomes.

QUESTIONS
WHAT IS KARYOTYPING?
Why Analyse Chromosomes and Genes?