Fundamentals of Anatomy and Physiology

Cellular Metabolism and Reproduction: Mitosis and Meiosis 77

Grows into

adult male or

adult female

Female Male

(diploid) (diploid)

2N 2N

Meiosis Meiosis

Sperm

(haploid)

N

(haploid)Egg^
Fertilization^
N

Figure 4- 12 The sexual cycle.

The Stages of Meiosis

The stages of meiosis are discussed next. Refer to Figure-
4 - 13 to follow the discussion.

Media Link

Watch an animation on meiosis

on the Student Companion

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(^) ®
Learning
Zygote (diploid) 2N Cengage
(^) ©
Prophase I
The DNA has already duplicated before the onset of
meiosis. Therefore, just like at the beginning of mito-sis in
interphase, each thread of DNA consists of two sister
chromatids joined at their centromere. In pro-phase I, the
duplicated chromosomes shorten, coil, thicken, and become
visible. It is here in meiosis that now something very
different occurs. Each chromo-some pairs up with its
homologue. Remember that our 46 chromosomes exist as
23 pairs. One mem-ber of each pair was inherited from our
mother and the other member of each pair from our father.
In