Question

Describe the individuals with the following chromosomal abnormalities:
1. Trisomy of chromosome 21.
2. XXY.
3. XO.

Hint:

These conditions are examples of Aneuploidy, which arises due to the failure of segregation of chromatids during cell division (non-disjunction).

Answer 1

Step 1: Trisomy of 21 (Down's Syndrome): Caused by the presence of an additional copy of chromosome number 21. Affected individuals have a short stature, small round head, furrowed tongue, partially open mouth, and broad palm with a characteristic palm crease. Physical and mental development is retarded.
Step 2: XXY (Klinefelter's Syndrome): Caused by an extra X chromosome in males (47, XXY). Such individuals have overall masculine development but also express feminine characters like development of breasts (Gynaecomastia). They are sterile.
Step 3: XO (Turner's Syndrome): Caused by the absence of one of the X chromosomes in females (45, XO). Such females are sterile as ovaries are rudimentary, and they lack other secondary sexual characters.