There are different types of cell division.

• 6.1 Immortal cells can spell trouble: cell division in sickness and in health.
• 6.2 Some chromosomes are circular, others are linear.
• 6.3 There is a time for everything in the eukaryotic cell cycle.
• 6.4 Cell division is preceded by chromosome replication.

Mitosis replaces worn-out old cells with fresh new duplicates.

• 6.5 Most cells are not immortal: mitosis generates replacements.
• 6.6 Overview: mitosis leads to duplicate cells.
• 6.7 The details: mitosis is a four-step process.
• 6.8 Cell division out of control may result in cancer.

Meiosis generates sperm and eggs and a great deal of variation.

• 6.9 Overview: sexual reproduction requires special cells made by meiosis.
• 6.10 Sperm and egg are produced by meiosis: the details, step by step.
• 6.11 Male and female gametes are produced in slightly different ways.
• 6.12 Crossing over and meiosis are important sources of variation.
• 6.13 What are the costs and benefits of sexual reproduction?

There are sex differences in the chromosomes.

• 6.14 How is sex determined in humans?
• 6.15 The sex of offspring is determined in a variety of ways in non-human species.
• 6.16 This is how we do it: Can the environment determine the sex of a turtle’s offspring?

Deviations from the normal chromosome number lead to problems.

• 6.17 Down syndrome can be detected before birth: karyotypes reveal an individual’s entire chromosome set.
• 6.18 Life is possible with too many or too few sex chromosomes.