Worksheet on non-disjunction:
(a) Fill in the cells below showing the NORMAL process of meiosis of the male’s sex chromosomes
(The large black chromosome is the X and the smaller red one is the Y). DO NOT show crossing over.
½ of the gametes will have the X chromsome and ½ of the gametes will have a Y chromosome.
Remember we are only showing the sex chromosomes, and there would be 22 other chromosomes in
each of the gametes.
(b) Fill in the cells below showing the process of meiosis of the male’s sex chromosomes with non-
disjunction occurring during meiosis I. DO NOT show crossing over.
prior to meiosis
prior to meiosis
sister chromatids split
but two end up in both
cells does not split
The black chromosome is
representing the large X
chromosomes, and the red
represents the Y-
chromosome
homologous pairs split
sister chromatids split
homologous pair does not
split normally the X and Y
chromosomes stay together
with the first split – they are
still duplicated.
no sex
chromosomes go
to this cell – due to
nondisjunction
