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574 Chapter 17 NEL

Meiosis II

Meiosis II occurs at approximately the same time in each of the haploid daughter cells.

However, for simplicity, consider the events in only one of the cells. (In Figure 4, both

cells from meiosis I are shown). During meiosis II, pairs of chromatids will separate and

move to opposite poles. Note that, unlike with mitosis and meiosis I, there is no repli-

cation of chromosomes prior to meiosis II.

Figure 4

During meiosis II, sister chromatids separate.

The cytoplasm separates,

leaving four haploid

daughter cells. The

chromosome number has

been reduced by half. These

cells may become gametes.

Sister chromatids of each

chromosome separate and

move to opposite poles.

Chromosomes line up at the

equatorial plate.

The centrioles in the two new
cells move to opposite poles
and new spindle fibres form.
The chromosomes become
attached to the spindle.

prophase II metaphase II anaphase II telophase II

Prophase II signals the beginning of the second meiotic division. During this stage, the

nuclear membrane dissolves and the spindle fibres begin to form.

Metaphase II follows prophase II. It is signalled by the arrangement of the chromo-

somes, each with two chromatids, along the equatorial plate. The chromatids remain

pinned together by the centromere.

Anaphase II can be identified by the breaking of the attachment between the two chro-

matids and by their movement to the opposite poles. This stage ends when the nuclear

membrane begins to form around the chromatids, now referred to as chromosomes.

The cell then enters its final stage of meiosis: telophase II. During this stage, the second

nuclear division is completed and then the second division of cytoplasm occurs. Four hap-

loid daughter cells are produced from each meiotic division.