Down's Syndrome & Trisomy 21 — NEET Biology
✅ Asked in NEET 2024Down's Syndrome: The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21). This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.
Down's syndrome results from trisomy of chromosome 21, meaning three copies instead of two. NTA tests whether students can identify the correct chromosome number and understand that this extra chromosome causes the characteristic features: short stature, round head, furrowed tongue, broad palm with crease, and retarded physical/mental development. Students often confuse it with other chromosomal disorders like Turner syndrome (45,X) or Klinefelter syndrome (47,XXY). Remember: Down's syndrome = 47 chromosomes total with three copies of chromosome 21 (written as 2n+1 for chromosome 21). This appears frequently because it's the most common autosomal trisomy compatible with life and demonstrates core inheritance principles.
This paragraph was tested 2 times in NEET.
In Down’s syndrome, the individual has 47 chromosomes. What causes this? (NEET 2024)
A disease caused by an autosomal primary non-disjunction is (NEET 2017)
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