2. karyology
The study of whole sets of
chromosomes is sometimes known
as karyology.
3. What is Idiogram ???
Diagrammatic representation of the gametic
chromosome set (n) of a species
Used to compare the karyotype of one species
with the other
Karyotype is represented diagrammatically
showing all the morphological features of
chromosomes.
4.
5. What is Karyotyping
a standard chart of
chromosomes isolated from a
cell at metaphase arranged in
order by size and structure of
physical landmark
6. The basic number of chromosomes in
the somatic cells of an individual or a
species is called the somatic number
and is designated 2n. Thus, in humans
2n = 46. In the germ-line (the sex cells)
the chromosome number is n (humans:
n = 23)
7.
8. Why do scientists look at chromosomes??
Scientists can diagnose or predict genetic
disorders by looking at chromosomes.
This kind of analysis is used in prenatal testing
and in diagnosing certain disorders, such as
Down syndrome,
or in diagnosing a specific types of
leukemia.
9. SPECIMENS USED
Peripheral Blood Cultured Skin Fibroblast
Bone Marrow Amniotic Fluid
10. How are chromosomes classified?
According to the site of the centromere
According to size
How are Chromosomes of similar size
and shape distinguished from one
another?
Chromosome Banding (Q banding,G
banding C banding, R banding)
12. CLASSIFICATION OF CHROMOSOMES FOR
KARYOTYPING
Group A: chromosomes 1,2,3
largest
metacentric and submetacentric
Group B: chromosomes 4,5
large
submetacentric
Group C: chromosomes 6,7,8,9,10,11,12
medium
submetacentric
13. CLASSIFICATION OF CHROMOSOMES FOR
KARYOTYPING
Group D: chromosomes 13, 14, 15
medium acrocentric
Group E: chromosomes 16, 17, 18
short metacentric or submetacentric
Group F: chromosomes 19, 20
short metacentric
Group G: chromosomes 21, 22
very short acrocentric
14. Preparing a Karyotype
Incubate Add chemical to
3-4 days stop mitosis in
metaphase
Lymphocytes are
harvested and
treated with
hypotonic solution
Swollen cells are
fixed, dropped in a
glass slide, dried
and stained
15. Types of banding
G-banding is obtained with Giemsa stain
following digestion of chromosomes with trypsin.
It yields a series of lightly and darkly stained
bands - the dark regions tend to be
heterochromatic, late-replicating and AT rich.
The light regions tend to be euchromatic, early-
replicating and GC rich. This method will
normally produce 300-400 bands in a normal,
human genome.
16. R-banding is the reverse of G-banding (the R
stands for "reverse"). The dark regions are
euchromatic (guanine-cytosine rich regions) and
the bright regions are heterochromatic (thymine-
adenine rich regions).
C-banding: Giemsa binds to
constitutive heterochromatin, so it stains
centromeres.
17. Q-banding is a fluorescent pattern obtained
using quinacrine for staining. The pattern of
bands is very similar to that seen in G-banding.
T-banding: visualize telomeres.
Silver staining: Silver nitrate stains the
nucleolar organization region-associated
protein. This yields a dark region where the
silver is deposited, denoting the activity of rRNA
genes within the NOR
18. The human karyotype
The normal human karyotypes contain 22
pairs of autosomal chromosomes and one pair
of sex chromosomes. Normal karyotypes
for females contain two X chromosomes and
are denoted 46,XX; males have both an X and
a Y chromosome denoted 46,XY. Any
variation from the standard karyotype may
lead to developmental abnormalities.
20. Digital karyotyping
Digital karyotyping is a technique used to
quantify the DNA copy number on a
genomic scale. Short sequences of DNA
from specific loci all over the genome are
isolated and enumerated.This method is
also known as virtual karyotyping.
23. Ploidy
Polyploidy, where there are more than two sets of
homologous chromosomes in the cells
Polyploid series in related species which consist entirely of
multiples of a single basic number are known as euploid
Polyploidy in lower plants (ferns, horsetails andpsilotales) is
also common
It is not occuring in humans..
It indicate genetical abnormality
24. Aneuploidy
Aneuploidy is a term used to describe a
chromosome problem, such as Down
syndrome, that is caused by an extra or
missing chromosome.
This would give rise to achromosome abnormality
such as an extra chromosome or one or more
chromosomes lost. Abnormalities in chromosome
number usually cause a defect in development.
Down syndrome and Turner syndrome are
examples of this.
