MP Board · Class 12 · Biology · Principles of Inheritance and VariationWhat are chromosomal disorders? Explain Down's syndrome, Klinefelter's syndrome, and Turner's syndrome with their causes and characteristic symptoms.

Introduction to Chromosomal Disorders\nChromosomal disorders are genetic conditions caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division cycle results in the gain or loss of chromosomes, a phenomenon known as aneuploidy. For example, Down's syndrome results in the gain of an extra copy of chromosome 21, whereas Turner's syndrome is characterized by the loss of an X chromosome in females.

1. Down's Syndrome

• Cause: It is caused by the presence of an additional copy of chromosome 21. This phenomenon is known as trisomy of chromosome 21, resulting from non-disjunction during gametogenesis.
• Symptoms: Affected individuals show retarded mental development, shortened stature, furrowed tongue, permanently open mouth, broad palm with a single palmar crease (simian crease), and underdeveloped genitalia.

2. Klinefelter's Syndrome

• Cause: This disorder arises due to the presence of an additional X chromosome in males, resulting in a karyotype of 47, XXY. It occurs due to non-disjunction of sex chromosomes during meiosis.
• Symptoms: Affected males have overall masculine development, but some feminine characters also appear, such as the development of breasts (gynecomastia), tall stature, sparse body hair, and they are sterile.

3. Turner's Syndrome

• Cause: This disorder is caused due to the absence of one of the X chromosomes in females, resulting in a karyotype of 45, XO. It occurs when an egg is fertilized by a sperm lacking a sex chromosome.
• Symptoms: Affected females are sterile as ovaries are rudimentary. They possess shield-shaped chest, webbed neck, short stature, underdeveloped breasts, and lack of secondary sexual characteristics.