Chromosomal anomalies LECTURE FOR BIOLOGISTS .ppt
- 2. Introduction • Teratology • Causes of congenital malformations: (a) Genetic factors: chromosomal abnormalities (b) Environmental factors: drugs, viruses • Types of chromosomal abnormalities: (a) Numerical (b) Structural
- 3. Causes of congenital malformations
- 4. Numerical Chromosomal Abnormalities • Changes in the number of chromosomes: • Polyploidy • Somatic cells contain multiples of haploid number of chromosomes • 3n, 4n, 5n etc. • Aneuploidy (Heteroploidy) • Deviation from the diploid number of chromosomes • 2n + 1, 2n -1 etc.
- 5. Mechanism of Polyploidy (a) Failure of pulling apart of 2 chromatids to opposite ends after metaphase stage of mitosis. (b) Reduplication of chromosomes without dissolving of nuclear membrane. (c) Failure of cytoplasmic division.
- 6. Types of Polyploidy 1. Autopolyploidy: even-numbered multiples of haploid number of chromosomes. e.g.- (a) Tetraploidy (23x4 or 92 chromosomes) (b) Hexaploidy (23x6 or 138 chromosomes) (c) Octaploidy (23x8 or 184 chromosomes) etc.
- 7. Types of Polyploidy 2. Allopolyploidy: odd-numbered multiples of haploid number of chromosomes. e.g.- (a) Triploidy (23x3 or 69 chromosomes)-commonest (b) Pentaploidy (23x5 or 115 chromosomes) (c) Heptaploidy (23x7 or 161 chromosomes) etc.
- 8. Mechanism of Aneuploidy Non-dysjunction: failure of separation of chromosomes during cell division. • Formation of 2 types of gametes (both abnormal) • Fusion of either of these abnormal gametes with a normal gamete can result in trisomy or monosomy • May involve autosomes or sex chromosomes
- 9. Normal 1st & 2nd meiotic division Two types of non-disjunction
- 10. Trisomies of Chromosomes • Presence of 3 copies of a chromosome • Trisomy of Autosomes (13,18,21) • Trisomy of Sex Chromosomes (XXX, XXY)
- 11. Trisomy of Autosomes • Trisomy 13 or D-trisomy (Patau syndrome) • Trisomy 18 or E-trisomy (Edward syndrome) • Trisomy 21 or G-trisomy (Down syndrome)
- 12. Trisomy 13 (Patau Syndrome) • 1st described by Bartholin (1657) & redefined by Patau (1960). • Chromosomal complement: 47,XX,+13 (female) or 47,XY,+13 (male) • Phenotype: Male or female • Incidence: 1:12,000 (increases with the age of mother)
- 13. Features of Patau Syndrome • Mental deficiency • Low birth weight • Abnormal development of frontal lobe • Absence of corpus callosum • Hypoplasia of cerebellum • Sloping forehead • Scalp defects • Malformed ears • Congenital heart defects • Renal tract anomalies • Microphthalmia • Bilateral cleft lip/palate • Polydactyly with rudimentary digits • Rocker-bottom heel
- 14. Patau syndrome
- 15. Patau syndrome
- 16. Trisomy 18 (Edward Syndrome) • Chromosomal complement: 47,XX,+18 (female) or 47,XY,+18 (male) • Phenotype: Male or female • Incidence: 1:8000
- 17. Features of Edward Syndrome • Mental deficiency • Growth retardation • Prominent occiput with elongated head • Webbing of the neck • Short sternum • Micrognathia • Low-set malformed ears • Ventricular septal defects • Renal anomalies • Clenched fists with overlapping of fingers • Hypoplastic nails
- 18. Edward syndrome
- 19. Trisomy 21 (Down Syndrome) • Chromosomal complement: 47,XX,+21 (female) or 47,XY,+21 (male) • Phenotype: Male or female • Incidence: 1:800 (increases with the age of mother)
- 20. Features of Down Syndrome • Short height • Severe mental deficiency with decline in the IQ with age • Brachycephaly with flat face and occiput • Flat and low nasal bridge • Upward slant to palpebral fissures • Malformed large ears • Epicanthal folds of the eyes • Brushfield spots in iris • Renal anomalies • Prominent and protruding tongue (scrotal tongue) • Simian crease • Clinodactyly of 5th digit
- 21. Down Syndrome
- 22. Down syndrome
- 23. Down syndrome
- 24. Down syndrome
- 25. REFERENCES 1. Essentials of Anatomy for Dentistry Students,1st Edition. 2. Langman’s Medical Embryology,11th Edition. 3. Human Embryology, 5th Edition.
- 26. MCQs 1. Patau syndrome is associated with trisomy of chromosome: a) 13 b) 15 c) 18 d) 21
- 27. MCQs 2. Rocker-bottom heel is associated with: a) Patau syndrome b) Edward syndrome c) Down syndrome d) None of the above
- 28. MCQs 3. Brushfield spots is a characteristic feature of: a) Patau syndrome b) Edward syndrome c) Down syndrome d) None of the above
- 29. MCQs 4. All of the following are trisomy of autosomes except: a) Edward syndrome b) Klinefelter syndrome c) Down syndrome d) Patau syndrome
- 30. MCQs 5. All of the following are examples of autopolyploidy except: a) Triploidy b) Tetraploidy c) Hexaploidy d) Octaploidy