MP Board · Class 12 · Biology · Principles of Inheritance and VariationExplain chromosomal disorders in humans with specific examples. Discuss Down's syndrome, Turner's syndrome, and Klinefelter's syndrome in detail.

Chromosomal Disorders in Humans

\nChromosomal disorders are caused due to the absence or excess or abnormal arrangement of one or more chromosomes. This is generally caused by non-disjunction, a failure of chromatids to segregate during cell division.

1. Down's Syndrome

• Cause: Down's syndrome is caused by the presence of an additional copy of chromosome number 21 (Trisomy of 21). The total number of chromosomes becomes 47 ($45 + XY$ or $45 + XX$).
• Symptoms & Features:
  • Affected individuals have short stature with small round head.
  • Furrowed tongue and partially open mouth.
  • Broad palm with characteristic palm crease (simian crease).
  • Physical, psychomotor, and mental development is retarded.
  • Congenital heart defects are common.

2. Turner's Syndrome

• Cause: This disorder is caused due to the absence of one of the X chromosomes, i.e., $45$ with $X0$. It affects females.
• Symptoms & Features:
  • Sterile females because ovaries are rudimentary.
  • Lack of secondary sexual characters.
  • Short stature, webbed neck, and shield-shaped chest.
  • Underdeveloped breasts and normal intelligence in most cases.

3. Klinefelter's Syndrome

• Cause: This disorder is caused due to the presence of an additional X chromosome resulting in a karyotype of $47$, $XXY$. It affects males.
• Symptoms & Features:
  • Overall masculine development, but feminine characters (development of breasts, known as gynaecomastia) are also expressed.
  • Individuals are sterile and cannot produce sperms.
  • Tall stature, sparse body hair, and often mild mental retardation.