This document discusses chromosomal aberrations, beginning with their definition as any atypical number or structure of one or more chromosomes. It describes the basic terms like karyotyping, chromatid, and chromosome constituents. There are two main types of chromosomal aberrations - numerical involving an abnormal number of chromosomes, and structural involving changes in chromosome structure. Numerical aberrations include aneuploidy, trisomy, monosomy, and polyploidy. Structural aberrations comprise deletion, duplication, fragile sites, inversions, ring chromosomes, and translocations. The document outlines several methods for diagnosing chromosomal aberrations prenatally such as ultrasound, fetal echocardiography, and

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

7. TYPES OF CHROMOSOMES

8. TYPES OF CHROMOSOMAL ABERRATIONS
Numerical Structural
1. Trisomy 1. Deletion
2. Monosomy 2. Duplication
3. Polyploidy 3. Fragile site
4. Mosaicism 4. Inversions
5. Ring chromosome
6. Translocation

9. 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 : Polyspermy, failed meiosis( diploid cell) , self fertilize (
tetraploid zygote)

10. 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

11. Structural abnormalities
1. Deletion : part of a chromosome segment is lost, may
be small or large portion
2. Duplication : section of chromosome is in duplicate,
usually less harmful. Extra genetic material causes birth
defects.
3. 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.

12. 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.

13. STRUCTURAL ABERRATION

14. 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

15. THANKS