Question

Describe the disorders from the following chromosomal abnormal arrangements: (i) Trisomy of Chromosome 21 (ii) XXY

Hint:

Down's = Trisomy 21 (47 chromosomes). Klinefelter's = XXY (47 chromosomes, male sterility).

Answer 1

(i) Trisomy of Chromosome 21 (Down's Syndrome): \[\begin{array}{rl} \bullet & \text{Caused by the presence of an extra copy of chromosome 21 (2n = 47).} \\ \bullet & \text{The condition arises due to non-disjunction of chromosome 21 during meiosis.} \\ \bullet & \text{Symptoms:} \\ \bullet & \text{Mental retardation and delayed cognitive development.} \\ \bullet & \text{Short stature, round face, slanting eyes, and flat nasal bridge.} \\ \bullet & \text{Heart defects and poor muscle tone.} \\ \end{array}\] \item More frequent in children of older mothers (>35 years). \end{itemize} (ii) XXY (Klinefelter's Syndrome): \[\begin{array}{rl} \bullet & \text{Caused by the presence of an extra X chromosome in males (47, XXY).} \\ \bullet & \text{Results from non-disjunction of sex chromosomes during gamete formation.} \\ \bullet & \text{Symptoms:} \\ \bullet & \text{Male individuals with tall stature and long limbs.} \\ \bullet & \text{Underdeveloped testes leading to sterility.} \\ \bullet & \text{Enlarged breasts (gynecomastia) and sparse facial/body hair.} \\ \bullet & \text{Reduced testosterone levels.} \\ \end{array}\] \end{itemize} Conclusion:
Both conditions are chromosomal disorders caused by abnormal segregation of chromosomes during meiosis. They affect physical, mental, and reproductive health.