Chromosomal aberration

chromosomal aberration, useful for Bsc nursing students of 2 nd yr.

1. CHROMOSOMAL ABERRATION Prepared by: Vijayakumar . M . B Lecturer, charuast university

2. MEANING OF ABERAATION Any departure or deviation from normal, usually expected. DEFINITION : any aberration in the shape, size or structure of a chromosome is called chromosomal aberration. It reflects an atypical number or a structure in one or more chromosomes.

3. Basic terms to be remembered Karyotyping : refers to a full set of chromosome from an individual, or a photographic arrangement of a set of chromosomes of an individual. Chromatid : either of the two daughter strands of replicated chromosome that are joined by centromere and separate during cell division. Constituent of chromosome: DNA, RNA , HISTONES (5 kinds) No of chromosomes: 22 pairs of autosomes& a pair of sex chromosomes. Diploid : 46. haploid : 23

4. Karyotyping

5. Structure of chromosome

6. Types of chromosomes

7. Types of chromosomal aberrations Numerical Structural Trisomy 1. Deletion Monosomy 2. Duplication Polyploidy 3. Fragile site Mosaicism 4. Inversions 5. Ring chromosome 6. Translocation

8. Numerical aberrations : ANEUPLOIDY : having too many or too few chromosomes. 1. TRISOMY : 3 copies of particular chromosome. Common trisomy is down syndrome, trisomy 21. Reason : fails to go to opposite poles of the dividing cells. 2. MONOSOMY: missing of a copy of chromosome. Ex: 45x, and monosomy are always lethal, the only compatible condition is turner syndrome( only one x chromosome) 3. POLYPLOIDY : more than normal diploid number of chromosome. Ex: triploidy – 6pxxx Tertroploidy – 92XXXX Reason : P olyspermy , failed meiosis( diploid cell) , self fertilize ( tetraploid zygote)

9. 4. Mosaicism : half of the cell have normal and the remaining have abnormal in term of structure or number It commonly seen in down syndrome , turner syndrome etc

10. Structural abnormalities Deletion : part of a chromosome segment is lost, may be small or large portion Duplication : section of chromosome is in duplicate, usually less harmful. Extra genetic material causes birth defects. Fragile site : constriction at sites other than centromere. There is more tendency to break. ex: X linked mental retardation, fragile X syndrome. 4. inversions: two breaks in chromosome & then reinserted by turning around.

11. 5. Ring chromosome : two breaks in the chromosome and these broken ends stick back together. 5. Translocation : transfer of all or a part of a chromosome from one to another.

12. Structural aberration

13. Diagnosis of chromosomal aberrations Ultrasound ( BPD, Nuchal space) Fetal echo cardiography Radiography Screening : a. measuring MSAFP( by yolk sac) – decrease in down syndrome b. Maternal unconjugated estriol - (decrease in down syndrome c. Maternal serum human HCG – (produced by trophoblast ) increase in down syndrome d. Maternal inhibin A level ( by placenta corpus luteum ) – increase in trisomy 21 e. Separation of fetal cells from maternal blood : Ex: FISH:- fluorescent insitu hybridization, to diagnose uneuploidy . Other invasive Embryoscopy fetal tissue sampling : - amniocentesis - Chorianic villai sampling - Cordocentesis

14. THANKS