Learn something new every day More Info... by email In the field
of genetics, "nondisjunction" is a technical term for a specific
defect in the way the chromosomes of a cell separate. This
defect creates a genetic mutation or defect in the cells
produced from the process. The resulting cells are called
aneuploid. There are two crucial stages of cellular division
when this defect can occur. The first stage is meiosis I, when
the homologous chromosomes fail to separate, while the second is
meiosis II, commonly known as mitosis, when the sister
chromatids do not separate properly. When nondisjunction occurs
during meiosis I, all of the resulting gametes, called daughter
cells, are affected. Two of the daughter cells will have an
extra chromosome, and the other two daughter cells will be
missing one chromosome. Only half of the resulting daughter
cells will be affected when this defect occurs during meiosis
II. Of the four resulting gametes, two will be normal, one will
have an extra chromosome, and one will be m