HUMAN BIOLOGY

368 Chapter 18

Anaphase

• Sister chromatids sepa-
  rate and move toward
  opposite spindle poles.

Metaphase

• Chromosomes align
  midway between
  spindle poles.

Prophase

• Chromosomes condense.


• Spindle forms and attaches
  chromosomes to spindle poles.


• Nuclear envelope breaks up.

Telophase

• Chromosome clusters arrive
  at spindle poles.


• New nuclear envelopes form.


• Chromosomes decondense.

Anaphase I

• Homologous chromosomes
  separate and move toward
  opposite spindle poles.

Metaphase I

• Chromosomes align
  midway between
  spindle poles.

Prophase I

• Chromosomes condense.


• Homologous chromosomes pair.


• Crossovers occur (not shown).


• Spindle forms and attaches
  chromosomes to spindle poles.


• Nuclear envelope breaks up.

Telophase I

• Chromosome clusters arrive
  at spindle poles.


• New nuclear envelopes form.


• Chromosomes decondense.

Anaphase II

• Sister chromatids sepa-
  rate and move toward
  opposite spindle poles.

Metaphase II

• Chromosomes align
  midway between
  spindle poles.

Prophase II

• Chromosomes condense.


• Spindle forms and attaches
  chromosomes to spindle poles.


• Nuclear envelope breaks up.

Telophase II

• Chromosome clusters arrive
  at spindle poles.


• New nuclear envelopes form.


• Chromosomes decondense.

Mitosis and Meiosis Compared

n    Mitosis occurs in somatic cells, while meiosis takes place

in germ cells. The diagram presented here summarizes the

similarities and key differences of these mechanisms.

The end results of mitosis and meiosis differ in a crucial

way (Figure 18.14). Mitosis produces genetically identical

copies of a parent cell. Meiosis is an important source of

genetic variation in the traits offspring will have.

Figure 18.14 Animated! This diagram compares the similarities and differences between mitosis and meiosis.

As in other diagrams in this chapter, maternal chromosomes are pink, and paternal chromosomes are blue. (© Cengage Learning)

18.9

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