At what point in cell division is a chromosome lost so that, after fertilization with a normal gamete, the result is a human zyg
ote with 45 chromosomes, including a single X chromosome? I. an error in anaphase I
II. an error in anaphase II
III. an error of the first postfertilization mitosis
IV. an error in pairing
Chromosomal abnormalities are caused when the chromosome pair fails to disintegrate through a process called non-disjunction. The non-disjunction of chromosomes usually takes place at the anaphase I or II of meiosis I which involves the X and Y chromosomes.
The abnormality observed with 45 chromosomes or reduction in one sex chromosome or 45, XO is caused when one X copy of a chromosome is completely absent in the cell.
The cause for the loss of one chromosome is the non-disjunction during meiosis I.
