Which disorder is being discussed in the following statements? i) Tri…

The correct answer is Option (3) → Down's syndrome

Chromosomal disorders are caused by the loss, gain or wrong arrangement of chromosomes. An extra copy of one chromosome is called trisomy.

Option (1) Turner's syndrome — Incorrect. Turner’s syndrome is caused by the absence of one X chromosome (45 with X0). The females are sterile and have rudimentary ovaries. It is not a trisomy of chromosome 21.

Option (2) Klinefelter's syndrome — Incorrect. Klinefelter’s syndrome is caused by an extra X chromosome, giving 47, XXY. Such individuals are male in form but show some female development, such as breast development, and are sterile.

Option (3) Down's syndrome — Correct. Down’s syndrome is caused by trisomy of chromosome 21. All three features in the question are the ones the book lists for it. Physical, psychomotor and mental development are also retarded.

NCERT Extract:
Chromosomal Disorders – “… Down’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 (Figure 4.16). Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.”

Figure 4.16 A representative figure showing an individual inflicted with Down’s syndrome and the corresponding chromosomes of the individual