Question

A 3-year-old child exhibited some early indication of Turner syndrome, which results from a 45,X chromosome composition. Karyotypic analysis demonstrated two cell types: 46,XX (normal) and 45,X. Propose a mechanism for the origin of this mosaicism.

Answer 1

Answer:

The answer is mitotic nondisjunction of X Chromosomes.

Explanation:

Nondisjunction is a type of error that occurs resulting in daughter cells with chromosome numbers that are abnormal (aneuploidy). Due to the error in chromosome numbers, it gives rise to conditions such as Down Syndrome (Trisomy 21) and Turner Syndrome (Monosomy X). Nondisjunction can be caused by;

1. Failure of separation to occur in a pair of homologous chromosome during meiosis I.

2. Failure of separation between sister chromatids in Meiosis II.

3. Failure of separation between sisters chromatids in mitosis.

This gives the 45,X in Turner syndrome. The other X chromosome is partly or completely missing. Hence, the female is born with only one X chromosome.