Meiosis and Non-disjunction

The following clip looks at the stages of meiosis and does a good job explaining it.

The next clip identifies the differences between male and female gamete formation.

The following clip looks at the process of non-disjunction in meiosis II which can lead to the development of monosomies or trisomies.

The second clip looks at the process of a non-disjunction in meiosis I which can lead to the development of monosomies or trisomies.

Notice the number of chromosomes in each gamete. Notice the difference in what is occuring with the spindle. How does non-disjunction in meiosis I differ from non-disjunction in meiosis II?