Chromosome abnormalities Ajith Sominanda Department of Anatomy Faculty of Medicine Peradeniya

1. Chromosome abnormalitiesAjithSominandaDepartment of AnatomyFaculty of MedicinePeradeniya

2. Development of cytogenetic techniques to analyze chromosomes led to discovery and characterization of chromosome disorders (1950s) • Within years (from 1956), the cause of Down syndrome (47,XX/XY+21) Turner syndrome (45,X) and Klinefelter sysndrome (47,XXY) was established • Now more than 20,000 chromosome abnormalities have been reported but these conditions are very rare in the population • Chromosome abnormalities are a major cause for early pregnancy loses

3. Types of chromosome abnormalities • Numerical abnormalities (Abnormal changes in the chromosome number in a cell) • Structural abnormalities (abnormalities of the chromosome structure • Others

4. Failure of chromosomes to seggregate (move) during cell division : Non-dysjunction Normal Gametes Mono somic gametes Nullisomic gametes

5. Non dysjunction • Occurs with advancing age; especially maternal age • Maternal oocytes have a long delay between different phase of the cell division • With advancing age, spindle formation become defective and leads to non dysjunction

6. Gametogenesis in female and risk of non dysjunction

7. Gametogenesis in male

10. Numerical abnormalities • Aneuploidy (loss or gain of one or more chromosomes) • Monosomies (loss of a single chromosome) • 45,X - Turner syndrome (loss of one sex chromosome) • Monosomy of autosomes are incompatible with life • Trisomies (Presence of an extra chromosome) • Trisomy 21 (Down’s syndrome) • Trisomi 18 (Edward’s syndrome) • Trisomi 13 (Patau Syndrome) • XXY (Klinefelter syndrome) • XXX (XXX females) • XYY (XYY males) • Tetrasomies (Presence of two extra chromosome)

11. Polyploidy • (Addition of one or more haploid set of chromosomes) • Triploidy (3n 46+23=69) • Tetraploidy (4n 46+46=92) • Retension of polar bodies or fertilization with 2 or 3 sperms can lead to polyploidy • Tetraploidy (23+23+23+23=92) • Triploidy (46+23=69) • Triploidy (23+23+23=69) 23 23 23 23 23 23 46 23 23 Ovum polar body

12. Monosomies (loss of a single chromosome) Turner syndrome • Karyotype is 45,X

13. Trisomies (Presence of an extra chromosome) Down Syndrome Trisomy 21 (47,XX/XY+21)

14. Trisomies (Presence of an extra chromosome) • Edward syndrome • Trisomi 18 (47, XX/XY, +18)

15. Trisomies (Presence of an extra chromosome) • Patau syndrome • Trisomi 13 (47, XX/XY, +13)

16. Trisomies (Presence of an extra sex chromosome) • Klinefelter syndrome (47, XXY) • Slightly femine figure • Has low IQ and Learning difficulty • Infertile

17. Trisomies (Presence of an extra sex chromosome) • XXX females (47,XXX) • Looks normal in phenotype • Slightly less IQ • Fertile

18. Trisomies (Presence of an extra sex chromosome) • XYY males • Tall • Aggressive • Low IQ and learning difficulties • Normal fertility

19. Structural abnormalities • Translocations • Deletions • Insertions • Inversions • Rings chromosmoes • Isochromosomes

20. Types of translocations

21. Insertion

22. Inversion

23. Mosaicism is caused by an error in cell division very early in the development of the unborn baby due to chromosome abnormality

24. Chimerism chimera or chimaera is a single organism composed of two or more genetically distinct cellspopulations from different zygotes