It's about basic cytogenetics and methods to study cyotogenetics

1. CYTOGENETICS
Group no. : GM21-16
Presented by :
• Disha
• Humayun
• Rakesh
• Rahul
• Arshiya
Guided by : Assyl mam

2. Cytogenetics -
Cytogenetics deals mainly with the study of
chromosomes and sex chromatin.

3. 46
In eukaryotes
Chromosomes reside in
the nucleus
In Interphase
Chromosomes are
coiled
portion
extended
portion
heterochromatin euchromatin
Human
Chromosome
complement
44
Autosomes ( in 22 pairs)
2
Sex chromosomes
X Y

4. Structure of a chromosome
p arm (short)
Centromere
q arm
(long)
Gene locus
Two identicle chromatids
• chroma means color and soma
means body.
• consist of two chromatids-joined
together by centromere
• have small units of heredity called
genes
• genes have specific position on
chromosomes called gene locus
• usually studied in metaphase of
mitosis

5. Cell cycle
Interphase - Mitosis - Interphase cycle

6. stages of mitosis

7. • Cell division can be
arrested at metaphase
by substances like
colchicine or its
derivatives.
• This permits us to
study metaphase
chromosomes.

8. Meiosis

9. Gametogenesis
• Gametogenesis in human beings
show sexual dimorphism.
• In males, the process is called
spermatogenesis, in females, it is
called oogenesis.

10. Spermatogenesis

11. Oogenesis

12. Human chromosome Before 1956
chromos. no. was
thought to be 48
Tjio and Levan demonstrated
that there are 46 chromo.
using refined cytogenetics
techniques
Types of chromosomes on the basis of position of
centromere:

13. Karyotyping
• Process of obtaining karyotype
• Karyotype- Photographs of individual
chromosomes arranged according to
standard classification. It is also
known as Ideograms

14. Chromosomal classification
frist attempt was made in 1960- by Denver,
Colorado (Denver Classification)
A -
1,2,3
B-
4,5
C-
6,7,8,9,10,
11,12 &X
D-
13,14
,15
E-
16,17,18
F-
19,20
G-
21,22,&Y
Basis of Classification includes chromosomal
feature
• Length of chromosome
• Placement of centromere
• Relative lengths of arms

15. Normal male chromosome complement 46, XY arranged according to the
standard classification

16. • In 1971, at Paris Conference,
more accurate ways to
identifying chromosome was
disccused
• based on various banding
patterns
• Now the Paris Nomenclature is
accepted all over the world
Paris Nomenclature
both p and q arms consist of regions that
are numbered 1, 2 and 3 starting from
the centromere
Regions are further subdivided
into bands
(to give a precise location)
eg.- RBI ( Retinoblastoma) locus is situated on chromosome 13
i.e. it’s precise location is 13 q 14 , means fourth band on the 1st
region of long arm of chromosome 13.

17. Peripheral Blood Culture

18. Blood Collection
from peripheral veins with the help of
heperinised syringe
Planting
collecting blood in vials and culturing it
Medium
Serum
Phytohaemagglutinin mitogenetic agent
Antibiotics controls bacterial growth
provide nuorishment to
cells
Incubation
3 days at 37°C
COLCHICINE
centrifugation tube

19. Supernatant is removed and the cells arrested at metaphase stage
are kept in Hypotonic solution
Cells get swell and chromosome get separated
Adding Fixatives
Staining
Q-banding
C-banding
G- banding
R-banding
NOR-staining
most commonly used
Giemsa stain

20. Applications of Karyotyping
Clinical Diagnosis congenital malformations, multiple system defects,
ambiguous genitalia
Gene Mapping loacalisation of genes on chromosomes
Role in Cancer karyotyping helps in determination of prognosis in the
cases of chronic myeloid leukaemia
Repeated fetal loss assesment of Chromosomal Aberrations
Prenatal Diagnosis revels chromosmal abnormalities in foetus

21. Sex chromatin
In 1949, Barr and
Bertram
found some of the cells show
Chromatin mass in nuclei
while studying
on female
observed only in females
but not in males

22. • Sex Chromosome is also known as Barr Body
• inactivated X chromosome
• Present in cell with more that one X chromosome
• Num. of barr body = no. of X Chro. - 1
• Demonstrated best in Buccal mucosa

23. Lyon’s hypothesis
• In female somatic cells, only one
X chromosome is active. The
second is inactive, Condensed
and appears in the form of sex
chromatin in interphase
• Inactivation occurs in early
embryonic life
• Inactivation is random but fixed

24. Mechanism of Inactivation of X
chromosome
• involves DNA methylation
• specially cytosine froms 5-methyl cytosine
• this alters gene activity
• methylation is responsible for inactivation of
genes
• Inactivation center is loacted at the proximal
part of the long arm of X chromosome

25. Genetic significance of X inactivation
1. Dosage compensation
2. Variability of expression
3. Mosaicism

26. Chromosomal Aberrations
• Deviation in number and structure of chromosome
1. Diplpoid - 2n=46
2. Haploid - n=23; in gametes
3. Polyploid - multiple of ‘n’ such as triploid = 69 or tetraploid = 92 chromosomes
4. Aneuploid - not exact multiple of ‘n’ such as 2n-1 or 2n+1
2n-1 in Turner Syndrome 45,XO
2n+1 in Down Syndrome 47, Trisomy of chromosome 21

27. “Genesis of Aneuploidy”

28. Structural Aberrations
Causes of structural aberrations:
• ionising radiations
• chemical agents
• and viruses
(i) Stable
• deletion
• inversion
• translocation
• isochromosome, etc.
(ii) Unstable
• dicentric
• ring
chromosome

29. 1.Deletion - loss of a part of chromosome
Terminal
deletion
eg. Cri-du-chat
Interstitial
deletion
eg. Microdeletion
Syndrome like -
Prader-Willi
Syndrome, Wilms
tumour with
anirida terminal deletion
of p arm of
chromosome
interstitial deletion of p
arm of chromosome, eg.
Wilims tumour with
aniridia (11p-)

30. 2. Translocation
piece of one chromosome breaks and
attaches to another chromosome
Has two types:
a) Robertsonian translocation - for example D/G
transloaction
• also known as centric prosses
b) Reciprocal translocation - exchange between
non-homologus chromosome
• balanced type of translocation as genetic
material is not lost

31. 3. Insertion
insertion
a fragment is transfered from a
chromosome to a non-homologus
chromosome
rare non-reciprocal translocation

32. 4. Inversion
pericentric
inversion
paracentric
inversion
when a section of a chromosome
breaks and get reattaches to itself in a
reverse order
Types
a) Pericentric - both arms are involved
b) Paracentric - only one arm is involved
Note: does not leads to abnormal phenotypes but
formation of abnormal gamets can leads to abnormal
progeny.

33. 5. Isochromosome 6. Ring Chromosome
arms of chromosome are mirror
image of each othrer
fusion of cut ends to form ring
structure

34. Factors Playing Role in Chromosomal Aberrations
1. Maternal age: females above 35 years
2. Non- disjunction gene: rare in humans but found in other organisms
3. Radiations: incresed frequency of Down Syndrome
4. Chromosomal abnormalities: balanced translocation in parents
5. Autoimmune disorders

35. Autosomal Abnormalities
• Trisomy
1. Trisomy 21 -
Down
Syndrome
(Mongolism)

36. Clinical features
• low IQ
• mentally retarded
• small cody stature
• hypotonia of muscles
• brachycephaly
• open mouth with
protruding tongue
• hands- short and broad

37. Edward Syndrome 47,XY +18
2. Trisomy 18
Edward syndrome

38. Clinical features
• mental retradation
• hypertonia
• small ears
• small mouth
• short sternum
• clenched fist
• rocker-bottom feet
do not live beyond few months but only few
may survive for about 15 years
may have Congenital heart defects such as
ventricular septal defect (VSD)

39. 3. Trisomy 13
Patau Syndrome or D-
trisomy • Infants have sloping
forehead
• hypertelorism
• microphthalmia
• postaxial polydactyly
• cleft lip and cleft palate
• congenital malformations
95% of the live born babies die
during infancy and those who
survive show mental retardation

41. • Deletion
Deletions Clinical Manifestations
Wolf-Hirschhorn syndrome 4p- Mental retardation, epilepsy, cleft lip/palate,
coloboma, hypospadias
Cri-du-chat syndrome 5p- Mental retardation, microcephaly,
hypertelorism, cry like mewing of cat
De Grouchy syndrome 18q- "Carp-mouth", mental retardation, abnormal
ears and tapering fingers
Ring chromosome Anti-
mongolism
21r Anti-mongoloid slant of eyes, hypertonia,
micrognathia, growth retardation and skeletal
abnormalities

42. Sex Chromosomal Abnormalities
• Turner Syndrome
Clinical feature
• short stature
• webing of neck
• cubitus valgus i.e. reduction in
the angle at elbow
• broader chest - widely spaced
nipples
• ovaries and uterus
underdeveloved
• secondary sexual character not
developed

44. • Polysomy X
• female phenotype almost
normal
• usually detected on
examination and
investigations for infertility
• have multiple physical
deffects
in the form of XXX,XXXX, or XXXXX

45. • Klinefelter Syndrome
• male phenotype is X
chromatin positive.
• first described by Harry
Klinefilterin 1942.
Clinical features
• tall ,thin and eunuchoid
• poorly developed secondary
sexual characters
• gynaecomestia in some
caese
• normal intelligence
• low verbal IQ.

46. • XYY Males
• Extra Y chromosome in
male phenotype.
• emotional immaturity and
impulsive character
• anti social behaviour
• greater frequency among
prisoners
probably result of non disjunction at second
meiotic division.

47. What is CHIMAERA ?

49. Chimaera is an individual having two or more
genetically different cell population derived
from more than one zygote

50. Naturally occuring two types-
(i) Dispermic Chimaeras (ii) Blood Group Chimaeras
Two genetically different
sperms (from different fathers)
fertilise two ova. Both zygotes
contributes to form dispermic
chimaera.
Exchange of cells across
placenta between dizygotic
twins leads to blood group
chimaera.

51. 1. Euchromatin represents:
a. Extended pale staining portion of chromosomes
b. Coiled dark staining portion of chromosomes
c. Both coiled and extended portions of
chromosomes
d. None of the above

52. 2. Which one of the following is true about the
primary oocytes?
a. All primary oocytes are formed in prenatal life.
b. All primary oocytes are formed at puberty.
c. All primary oocytes are formed after menarche.
d. Primary oocytes are formed continuously from puberty until
menopause.

53. 3. In which phase of meiosis I,
the primary oocytes remain
suspended?
a. Prophase
c. Anaphase
b. Metaphase
d. Telophase
4. Which one of following
chromosome complement is
normally present in the daughter
cells resulting from meiosis I?
a. Polypoid
b. Aneuploid
c. Diploid
d. Haploid

54. 5. Second meiotic division in
oogenesis usually completes
when the female germ cell is in
a. Ovary
c. Uterine cavity
b. Ampulla of uterine tube
d. Cervical canal
6. "Human chromosome
complement has 46 chromosomes"
was established in the year
a. 1936
b. 1952
C. 1956
d. 1969

55. 7. Name the four types of chromosomes
depending upon the placement of centro
mere.
8. How many Barr bodies are seen in a cell?
9. How is inactivation of X chromosome
achieved?
10. Where is the inactivation centre?

56. 11. Which one of the
following banding
techniques is routinely used
in chromosome analysis?
a. C-banding
b. G-banding
c. Q-banding
d. R-banding
12. Edward syndrome is:
a. Trisomy 21
c. Trisomy 13
b. Trisomy 18
d. Trisomy 8

57. 13. Cri-du-chat syndrome
is:
a. Deletion involving short arm
of chromosome 5
b. Deletion involving long arm
of chromosome 5
c. Interstitial deletion of short
arm of chromosome 11
d. Deletion of terminal part of
long arm of chromosome 11
14. Which one of the
following syndrome
patients exhibit webbing of
neck?
a. Klinefelter syndrome
c. Turner syndrome
b. Down syndrome
d. Edward syndrome

58. 15. Which one of following
karyotype is found in
Klinefelter syndrome patients?
a. 45,XO c. 47,XXX
b. 47,XXY d. 47,XYY
16. Which one of the following
holds true about XYY males?
a. They are highly intelligent
b. They are impulsive and have
criminal tendency
c. They have short stature
d. Their extra Y makes them more
fertile

59. THANK YOU