2. LECTURE – 3 Learning objectives
Cytogenetics
Chromosome
Chromosomal disorders (autosomal)

3. Study of chromosomes by morphological analysis
CYTOGENETICS
Karyotyping
Study of chromosomes by morphological analysis
by detecting errors in chromosome # / structure
by study under microscope, photography & image analysis

4. CYTOGENETICS METHODOLOGY
Bone marrow, cancers, testis ; lymphocytes with addition PHA
Staining method : G/Q/R bands
Special methods : C, G, G-II, NOR, DAPI, T staining , SKY
Special culture - BRDU, sister chromatid exchange (SCE)

5. Karyotyping
Harvesting procedure

7. CHROMOSOME STRUCTURE TTAGGG Chromatids Centromere p / q arms Telomere
Satellites
TTAGGG

8. Xp2.13

9. CHROMOSOMAL DISORDERS
Etiology
Late maternal age
Irradiation
Drugs / chemicals
Viruses
After35

10. MECHANISMS ALTERING CHROMOSOME #
Non – disjunction
Anaphase lag
Multiple gametic fertilization

11. Cytogenetic nomenclature
Aneuploidy : variation # (2n + 1 / –1)
Hyperploidy - > 46 chromosomes
Hypoploidy - < 46 chromosomes
Trisomy / monosomy : 3/one in a pair
Haploid - 1 single set (23) : chromo -
Euploid: x haploid: diploid, tetraploid
Mosaicism: presence of more than 1 cytogenetically distinct cell lines

12. Mosaicism

14. STRUCTURAL CHROMOSOMAL ABERRATIONS

15. CYTOGENETIC NOMENCLATURE
Normal: 46, XX / 46, XY
Monosomy: 45, X
Trisomy: 47, XX, +21 / 47, XXY
Deletion : 46, XY, del(5) (p13)
Inversion: 46, XY, inv(5) (p13-15)
Ring chromosome: 46, XY, r(14)
Isochromosome: 46, XY, i(Xq)
Translocation: 46, XX, t(2:5)(q31; p14)
Mosaicism: 46, XX / 47, XX, +21

17. CYTOGENETIC DISORDERS
Non - disjunction / anaphase lag :
gametogenesis – trisomy / monosomy
in early development in mosaicism
Monosomy : autosome incompatible with life, some trisomies may be
Monosomy / trisomy of sex chromosomes more compatible
Autosomal mosaicism less common
Structural aberration : chromosomes

18. CYTOGENETIC DISORDERS
Cytogenetic disorders involving autosomes: Down syndrome, Edward syndrome, Patau synd.
Cytogenetic disorders involving sex chromosomes : Klinefelter syndrome, XYY syndrome, Turner syndrome, XXX/XXXX syndromes

19. DOWN SYNDROME

20. DOWN SYNDROME TRISOMY 21
Most common genetic cause of mental retardation in children
Incidence : 1 / 800 live births
Maternal age : 1 in 1550 below 20 year, 1 in 25 over 45 years
Parents : of normal karyotype
Most meiotic non – disjunction
95% extra CH of maternal origin

21. DOWN SYNDROME Karyotype – trisomy 95% : 47, XX, +21
Translocation 4%: 46, XX, +t (14q 21q)
Mosaic type 1% : 46, XX / 47, XX,+21

22. CLINICAL FEATURES
Facial profile: flat, oblique palpebral fissures, epicanthic folds
Severe mental retardation
Congenital heart dis., septal defects
High risk of acute leukemia
Serious infections are common
Premature Alzheimer's dis. after 39
Average life expectancy of 30 yrs

24. CRI du CHAT SYNDROME Karyotype : – 5p Clinical features :
Mewing cat like cry
Severe mental retardation
Congenital heart disease
Survival: some into adult life

26. Mother nature stumbling !
SnapShot
Mother nature
stumbling !

27. Beautiful young people are accidents of nature.
Graceful old people are the work of art. .

28. Thank You