Chromosomal aberrations refer to disruptions in the normal chromosomal content of a cell and are major causes of genetic conditions in humans. There are two main types of chromosomal aberrations: numerical abnormalities which involve an atypical number of chromosomes, and structural abnormalities which alter the structure of chromosomes. Examples of numerical abnormalities include aneuploidy, such as trisomy which is the presence of three copies of a chromosome instead of the normal two copies. Structural abnormalities include deletions, duplications, inversions, and translocations which involve portions of chromosomes being removed, duplicated, inverted, or transferred between chromosomes. Common genetic disorders associated with chromosomal aberrations include Down syndrome, Klinefelter syndrome

1. Chromosomal Aberrations
P R E S E N T E D B Y
D R . A N J A L I N A I K

2. Functions of chromosomes
• 1. They contain hereditary information in the form of genes and act as
hereditary vehicle.
• 2. They control division, growth, metabolism and differentiation of cell.
• 3. The ploidy of chromosomes determines the expression of gametophyte or
sporophyte generation.
• 4. Sex chromosomes determine sex of the individuals.
• 5. Crossing over and aberrations of chromosomes introduce variations in
population.

3. What are chromosomal aberrations?
• Chromosomal aberrations are disruptions in the normal chromosomal
content of a cell
• Major cause of genetic conditions in humans
• May be gain OR loss of chromosomal DNA
• May involve single OR multiple chromosomes

4. Major types of aberrations
• Numerical abnormalities
Pertaining to an atypical number of chromosomes seen in the cell
Eg: Aneuploidy, Polyploidy, Trisomy, etc
• Structural abnormalities
Involving altered structure of the chromosome
Four types: Deletions, Duplication
Inversion and Translocation

5. Numeric aberrations
• Based on number of chromosomes that are added / missing, it can be
classified as
• Aneuploidy: Refers to an abnormal number of chromosomes
Monosomy: Lack of one chromosome of the normal complement
Disomy: Presence of two copies of a chromosome
Trisomy: Presence of three copies of a chromosome, instead of two
Tetra/Pentasomy: Presence of four or five copies (respectively) of the
chromosome

6. Non-disjunction in chromosomes
• Nondisjunction ("not coming apart") is the failure of chromosome
pairs to separate properly during meiosis stage I or stage II
• This could arise from a failure of homologous chromosomes to
separate in meiosis I, or the failure of sister chromatids to separate
during meiosis II or mitosis
• This error causes an imbalance of chromosomes, and the cell is said
to be aneuploid

8. NON-DISJUNCTION

9. NUMERICAL ABERRATIONS

10. ANUEPLODY-TRISOMY

11. Downs Syndrome

12. Polyploidy
• Polyploidy is a term used to describe the chromosomal conditions
of cells and organisms that contain more than two paired
(homologous) sets of chromosomes.
• Two types:
Autopolyploidy
(involving same species)
Allopolyploidy
(involving different species)

13. POLYPLOIDY

14. POLYPLOIDY
IN WHEAT

16. STRUCTURAL ABERRATIONS

17. Structural aberrations
• The altered structure of a chromosome may exist in several forms:
Deletion: a part of the chromosome is missing or deleted.
Duplication: a portion of the chromosome is duplicated, leading to extra genetic material
Translocation: a portion of one chromosome is transferred to another chromosome
Inversion: a portion of the chromosome breaks off, inverts itself and reattaches, rendering that part
of the DNA inverted
Rings: a part of the chromosome breaks off and forms a ring
Isochromosome: loss of one arm of the chromosome followed by its replacement with an exact
copy of the other arm

18. Inversion

20. Translocations

21. Translocation in humans causing acute
myelogeneous leukaemia

22. Types of Inversion

23. Inversions contd.
• Inversions occur when a chromosome breaks in two places and the resulting
piece of DNA is reversed and re-inserted into the chromosome.
• Inversions that involve the centromere are called pericentric inversions; those
that do not involve the centromere are called paracentric inversions

24. Formation of a ring Isochromosome

25. Genetic disorders associated with chromosomal
aberrations
• Cri du chat syndrome: deletion in short arm of chromosome 5
• Down syndrome: trisomy of chromosome 21
• Edward’s syndrome: trisomy of chromosome 18
• Jacobsen syndrome: deletion of terminal region of chromosome
11
• Klinefelter’s syndrome: extra X chromosome in human males
• Turner syndrome: monosomy X in females (1 X chromosome
instead of 2)