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CBSE Class 12-science Answered

give an account of the chromosomal disorder in human with reference to downs syndrome klinefelters syndrome and turners syndrome
Asked by ap996969 | 19 Feb, 2019, 12:23: AM
answered-by-expert Expert Answer

Chromosomal disorders in humans:

Down’s syndrome

  • It is an aneuploid, trisomic disease caused by the presence of extra chromosome No. 21.
  • The egg has 24 chromosomes instead of 23 and the offspring has 47 chromosomes (45 + XY/45 + XX) instead of 46 chromosomes.
  • The presence of three chromosomes of the same kind is called trisomy.

Klinefelter’s syndrome

  • It is caused by the XXY genotype which results from the union of a non-disjunct XX egg and a normal Y sperm or a normal X egg and an abnormal XY sperm. 
  • The individual has 47 chromosomes (2n+1).

Turner’s syndrome

  • It is caused by the XO genotype which results from the union of an abnormal O egg with a normal X sperm or a normal X egg and an abnormal O sperm.
  • The individual has 45 chromosomes (2n−1).
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