The major difference between prophase I and prophase II is the genetic recombination process that occurs during prophase I, but does not repeat in prophase II. During prophase I, the duplicated homologous pairs line up and cross over, which is the process by which the chromatids exchange genetic information. Because this process occurs during prophase I, it does not need to repeat during prophase II.
Prophase I and II are the first stages of the two-phase meiosis process, which is cell division responsible for producing the sex cells or gametes that create genetic variation. The resulting gametes each have half of the genetic material from the original parent cell. According to Prentice Hall, during prophase I, two non-sister chromatids line up to form a tetrad and exchange genetic information. Because each non-sister chromatid is from a paternal cell and maternal cell, genetic variation is created as each cell crosses over or exchanges information with the other. Due to the duration of this process, prophase I consumes 90 percent of the time of a two-part meiosis process; hence, prophase I is considerably longer than prophase II.
During prophase II, which occurs during the second phase of meiosis known as meiosis II, the nuclear envelope breaks down, and the spindle apparatus forms. Then, the chromosomes begin to migrate down the center of the cell. These processes also occur during prophase I.