KARYOTYPING

 The orderly arrangement of the chromosomes according to length, position of centromere,
banding pattern is called karyotyping.
 A karyotype refers to a full set of chromosomes from an individual which can be compared to a
normal karyotype for the species via genetic testing.
 A chromosome anomaly may be detected or confirmed in this manner.
Procedure:
 Peripheral blood is collected in a heparinized syringe.
 Blood is cultured in a suitable medium with addition of phytohaemagglutinin.
 The culture vials are incubated for three days
 Colchicine is added after 3days which arrests the WBC’S in metaphase.
 The contents are centrifuged and cells are separated and treated with hypotonic solution.This
makes the cells swell up and disperse the chromosomes. These are dropped onto a chilled slide
stained with Trypsin Giemsa stain.
 Metaphase spreads are analysed under microscope where each chromosome is identified for the
abnormality, then photographed, cut and pasted in order.
 Chromosomes are classified into 7 groups and pasted accordingly- Group A- 1, 2, 3; group B- 4, 5;
group C- 6-12, X; group D- 13, 14, 15; group E- 16, 17, 18; group F- 19, 20; group G- 21, 22, Y
 Recently there is automatic karyotyping system available where the software does the necessary
karyotyping, but there should be manual checking before reporting.
Abnormalities of chromosome
 Chromosome anomalies usually occur when there is an error in cell division following meiosis or
mitosis. There are many types of chromosome anomalies. They can be organized into three basic
groups,
 Numerical anomalies
 structural anomalies
 mosaicism.
Numerical anomalies
When it involves the loss or gain of one or more chromosomes, it is called aneuploidy. When it
involves one or more sets of chromosomes it is called polyploidy. Example- Turner syndrome (XO),
Klinefelter syndrome(XXY), Down syndrome (trisomy 21)
Structural anomalies

a part of the chromosome is lost or gained. When chromosome complement is complete with no
loss or gain of genetic material, it is called balanced structural abnormality which is usually
harmless. When chromosome complement contains less or more amount of genetic material, it is
called unbalanced structural abnormality. Different types of structural abnormalities are-
translocation, deletion, duplication, insertion, inversion, ring, isochromosome
Mosaicism:
is defined as presence of two or more cell lines in an individual or in a tissue that differ in
genetic constitution but derived from a single zygote. It usually results from non-disjunction in an
early embryonic mitotic division with the persistence of more than one cell line. For example, the
two chromatids of chromosome 21 fails to separate at the second meiotic division in a human
zygote, it would result in four cell zygote having two cells with 46 chromosomes, one cell with 47
chromosomes and one cell with 45 chromosomes.
Non-disjunction
 Failure of separation of homologous chromosomes in meiosis 1 or sister chromatids in meiosis 2 /
mitosis during anaphase is called non-disjunction.
 If non disjunction occurs during meiosis, one daughter cell will have one extra chromosome (24)
and the other will have one chromosome less (22). The daughter cell with one extra chromosome
fertilizes with normal gamete it leads to trisomy and the daughter cell with one chromosome less
fertilizes with normal gamete it leads to monosomy in the offspring.
 If non disjunction occurs during mitosis it leads to mosaicism.