Question

Due to non-disjunction of chromosomes during spermatogenesis, sperms carry both sex chromosomes (22A + XY) and some sperms do not carry any sex chromosome (22A +O). If these sperms fertilise normal eggs (22A + X), what types of genetic disorders appear among the offsprings?

• A. Down's syndrome and Turner's syndrome
• B. Down's syndrome and Cri-du-chat syndrome
• C. Turner's syndrome and Klinefelter's syndrome
• D. Down's syndrome and Klinefelter's syndrome

Answer 1

Answer: (C)

Turner's syndrome and Klinefelter's syndrome

Turner syndrome is caused by a partial or complete absence of one of the X chromosomes in a female. A single X chromosome is the most common cause of miscarriage. Approximately 60% of females with Turner syndrome have a single X chromosome in all cells analyzed. Twenty percent are mosaic in which some of their cells have 2 X chromosomes while some have a single X. A small percentage of females with Turner syndrome have a part of one X chromosome in a ring formation.

Klinefelter syndrome is caused by the addition of an X chromosome. Normally, males have 46 chromosomes with one X and 1 Y chromosome. In the case of Klinefelter syndrome, the male has 2 X chromosomes and 1 Y chromosome. The presence of a Y chromosome is necessary for an individual to be male. The X chromosome carries more genetic information than is present on the Y chromosome. To prevent females from having additional genetic information the majority of one of the X chromosomes is inactivated. While the majority of this additional X chromosome is inactivated, there are pseudoautosomal genes which remain active on the inactivated X chromosome. In Klinefelter syndrome, it is this additional genetic information that is believed to result in the medical problems and clinical features.