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NEL Cell Division 577

Section17. 3

prophase metaphase anaphase telophase

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

(b)Meiosis II

The chromosomes condense,
becoming shorter and thicker.
The centrioles assemble and
spindle fibres attach to the
centromeres of the
chromosomes. The nuclear
membrane starts to dissolve.

Chromosomes line up at the

equatorial plate. The nuclear

membrane completely dissolves.

The centromeres divide and

the resulting chromosomes,

formerly chromatids, move to

opposite poles of the cell. An

identical set of chromosomes

moves to each pole.

Chromosomes lengthen

again, the spindle fibres

dissolve, and a nuclear

membrane forms around

the chromosomes.

(a)Mitosis

Figure 8
Comparison of the stages in (a)mitosis and (b)meiosis II. In mitosis, homologous
chromosomes are separated, giving rise to genetically identical sister cells. In meiosis II, the
sister chromatids in the products of meiosis I separate as the cells divide again. This gives rise
to four genetically different sex cells.