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Q5(b) · UPSC Civil Services Mains 2015 · Anthropology GS 1 · 10 marks · 1 min read

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Down's Syndrome.

Topic: Autosomal aberrations. Syllabus: (c) Autosomal aberrations—Down syndrome, Patau, Edward and Cri-du-chat syndromes. Same official PYQ from year-wise 2015 and Autosomal aberrations.

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Revision summary

Down’s syndrome is usually trisomy 21 from meiotic non-disjunction. Lejeune linked the phenotype to the extra chromosome. Translocation and mosaic forms exist. Maternal age raises risk of the common form. Counselling uses karyotype; racial labels are obsolete.

Model answer

Introduction

Down’s syndrome is a chromosomal condition, usually trisomy 21. Anthropology meets it in human genetics, growth, and counselling.

Body

Cause

  • John Langdon Down described the phenotype. Lejeune showed an extra chromosome 21.
  • Most cases are non-disjunction in meiosis, risk rising with maternal age.
  • Translocation Down’s can be inherited from a balanced carrier. Mosaics are milder in some tissues.

Features and care

  • Hypotonia, a flat facial profile, single palmar crease, and a risk of heart defects are common.
  • It is not a ‘race type’. Older racial labels were a scientific error.
  • Genetic counselling uses karyotype, and now NIPT, without treating the child as a social rank.

Flow diagram

flowchart TD
  DS[Down syndrome] --> T21[Trisomy 21]
  DS --> TR[Translocation]
  DS --> MO[Mosaic]
  T21 --> ND[Meiotic nondisjunction]

Conclusion

Down’s syndrome is trisomy 21 in most cases. The anthropological task is accurate cytogenetics and humane counselling, not a racial cartoon.

Quick related

Students also ask

  • Longitudinal method of studying growth.

    Next question in the 2015 paper (Q5). View answer →

  • Is every case inherited from a parent?

    No. Most are new non-disjunction. Translocation cases need parental karyotypes.

  • Does paternal age matter as much?

    The strong, replicated risk is maternal age for free trisomy 21.

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