Cell Division and Mitosis
- Dividing Cells: The Bridge Between Generations
- Overview of Division Mechanisms
- Mitosis and meiosis are eukaryotic nuclear division mechanisms that lead to the
distribution of DNA to new nuclei in forthcoming daughter cells.
- Mitosis is used by multicelled organisms for
development, growth, and repair.
- Meiosis occurs only in germ cells.
- Some Key Points About Chromosomes
- Each chromosomes is a molecule of DNA with proteins.
- The Cell Cycle
- The cell cycle is a cells life.
- Most of a cells existence (about 90 percent) is spent in
occupies only a small part.
- During interphase the cells mass increases
- Some cells are arrested in interphase and never divide again (example: brain cells).
- Stages of MitosisAn Overview
- The four sequential stages of mitosis are:
- Comparison of Asexual and Sexual Reproduction
- In asexual reproduction, one parent passes a duplicate of
its genetic information to its offspring, which can only be genetically identical clones
of the parent.
- In sexual reproduction, each parent contributes [one gene]
for each trait.
- Two Divisions, Not One
- In some ways meiosis resembles mitosis:
- From Gametes to Offspring
- Gamete Formation in Animals
- The life cycle of multicelled animals proceeds from meiosis to gamete formation Þ fertilization Þ growth by mitosis.
- In males, meiosis and gamete formation is called spermatogenesis.
- In females, meiosis and gamete formation is called oogenesis.
- More Gene Shufflings at Fertilization
- The diploid chromosome number is restored at fertilization when two very different
gamete nuclei fuse to form the zygote.
- The variation present at fertilization is from three sources:
- Crossing over occurs during prophase I.
- Random alignments at metaphase I lead to millions of combinations of maternal and
paternal chromosomes in each gamete.
- Sexual selection: of all the genetically diverse gametes produced, chance will
determine which two will meet.
- Meiosis and Mitosis Compared
- Both are eukaryotic processes.
- Mitotic cell division produces clones; this type of
division is common in asexually reproducing organisms and in the growth process.
- Meiosis occurs only in the germ cells used in sexual reproduction; it gives rise to