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
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.
PYQ trend
When UPSC asked this
Related PYQs from other years, newest first. Open a question to read it.
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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? -
2023 · Q8(b) · Anthropology GS 1 · 15 marks
Describe the causes of structural abnormalities of chromosomes with suitable examples. -
2021 · Q4(c) · Anthropology GS 1 · 15 marks
"Chromosomal aberrations can play havoc with the human body and mind." Explain with suitable examples -
2016 · Q7(b) · Anthropology GS 1 · 15 marks
Explain the significance of screening and counseling for genetic disorders.
More from this topic
Q3(a) · UPSC Mains 2024 · Anthropology GS 1 · 20 marks
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
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.
Q4(c) · UPSC Mains 2021 · Anthropology GS 1 · 15 marks
"Chromosomal aberrations can play havoc with the human body and mind." Explain with suitable examples
Numerical and structural aberrations (disorders).
Aberrations are numerical or structural changes of chromosomes. Down syndrome is trisomy 21 with body and cognitive effects. Turner is 45,X; Klinefelter is 47,XXY; both alter gonads and sometimes learning. Deletions and unbalanced translocations can be as severe as extra chromosomes. Outcomes vary; counselling and care matter as much as the karyotype name.
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