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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What is an anthropometric somatotype? Describe Heath and Carter's method of somatotyping
Next question in the 2015 paper (Q7). View answer →
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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.
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