Revision summary
Numerical aberrations are aneuploidies from non-disjunction. Down, Edwards, Patau, Turner, and Klinefelter are type cases. Structural changes include deletion, inversion, and translocation. Familial Down’s may follow a Robertsonian 14;21. Microarray and FISH extend the old karyotype.
Model answer
Copper italics in this answer — like this — are the key facts. Each one is unpacked in the Facts & figures rail.
Introduction
Chromosomal aberrations are changes in chromosome number or structure. They are a major class of human genetic disease and of counselling cases.
Body
Numerical
- Aneuploidy from non-disjunction: trisomy 21 (Down), trisomy 18 (Edwards), trisomy 13 (Patau).
- Sex chromosomes: XO Turner, XXY Klinefelter, XYY, and XXX.
- Polyploidy is rare in liveborn humans and usually lethal.
Structural
- Deletion: cri-du-chat (5p).
- Duplication and inversion may be balanced in a parent and unbalanced in a child.
- Translocation: Robertsonian 14;21 can cause familial Down’s. Reciprocal translocations appear in recurrent miscarriage.
- Isochromosome and ring chromosomes are rarer teaching types.
Detection and meaning
- Karyotype, FISH, and now chromosomal microarray catch what light microscopy misses.
- Mosaics, as in some Turner and Down cases, blunt the textbook phenotype.
- Anthropology uses these examples to teach that ‘type’ is cytogenetic, not a racial grade.
Flow diagram
flowchart TD CA[Chromosomal aberration] --> N[Numerical aneuploidy] CA --> S[Structural deletion translocation] N --> EX1[Down Turner Klinefelter] S --> EX2[Cri-du-chat Robertsonian]
Conclusion
Human chromosomal aberrations are numerical or structural. Down, Turner, Klinefelter, cri-du-chat, and Robertsonian translocation are the standard illustrations.
Quick related
Students also ask
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Are all aberrations visible on a routine karyotype?
No. Microdeletions need FISH or array.
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Can a balanced carrier be healthy?
Yes. Risk appears at meiosis, as unbalanced gametes.
Same topic · past papers
UPSC has asked this before
These previous-year questions sit on the same topic. Open one to practise the earlier ask.
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2026 · Q3(c) · Anthropology GS 1 · 15 marks
Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples -
2024 · Q3(a) · Anthropology GS 1 · 20 marks
What is meant by karyotype? How does its analysis help in diagnosis of the chromosomal aberrations in man? -
2021 · Q4(c) · Anthropology GS 1 · 15 marks
"Chromosomal aberrations can play havoc with the human body and mind." Explain with suitable examples
More from this topic
Q3(c) · UPSC Mains 2026 · Anthropology GS 1 · 15 marks · Solution
Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples
Numerical and structural aberrations (disorders).
Numerical chromosomal aberrations arise from non-disjunction during cell division, leading to abnormal chromosome numbers. Autosomal abnormalities such as Down syndrome, Patau syndrome, and Edwards syndrome cause severe physical and cognitive developmental delays. Sex chromosome abnormalities like Turner syndrome and Klinefelter syndrome result in distinct endocrine, reproductive, and morphological manifestations. Understanding these genetic variations provides essential insights into human variation, heredity, and clinical diagnostics.
Q3(a) · UPSC Mains 2024 · Anthropology GS 1 · 20 marks · Solution
What is meant by karyotype? How does its analysis help in diagnosis of the chromosomal aberrations in man?
Numerical and structural aberrations (disorders).
Karyotype means chromosome complement; karyogram is its ordered image. Metaphase arrest, hypotonic spreading and G-banding permit homologous pairing and notation. It diagnoses trisomy 21, Turner, Klinefelter and other numerical aberrations. It also finds large deletions, inversions and balanced or unbalanced translocations. Multiple cells must be examined for mosaicism. A normal karyotype does not exclude microdeletions or single-gene disease; use FISH, microarray or sequencing appropriately.
Q8(b) · UPSC Mains 2023 · Anthropology GS 1 · 15 marks · Solution
Describe the causes of structural abnormalities of chromosomes with suitable examples.
Numerical and structural aberrations (disorders).
Structural abnormalities rearrange chromosome parts after breakage or unequal crossing-over. Types are deletion, duplication, inversion, translocation, ring, and isochromosome. Cri-du-chat is 5p deletion; 22q11 is a common microdeletion. Philadelphia t(9;22) is a somatic translocation in CML. Robertsonian 14;21 can cause translocation Down syndrome. Balanced parental carriers explain some recurrent unbalanced offspring.