Review of Mitosis

Prophase

Metaphase

Anaphase

Telophase

1

2

3

4

Overview of Mitosis: Prophase, Metaphase, Anaphase, Telophase

Overview of Meiosis: Prophase I, Metaphase I, Anaphase I, Telophase I,

Prophase II, Metaphase II, Anaphase II, Telophase II

Prophase I

• In prophase I:– The nuclear

membrane breaks down

Metaphase I

• In Metaphase I:• This is different

than Metaphase in Mitosis

• Chromosomes line up in pairs

• Kinetochore fibers attach to centromeres

One thing that happens during metaphase I is that parts of the sister chromosomes can actually cross-over and switch. This allows for new combinations of genetic material. (This is why we don’t look just like

our moms or dads) This is called genetic recombination.

Anaphase I

• In Anaphase I– Homologous

chromosomes seperate

• The chromatids do not seperate

Telophase I

• In Telophase I– Cells Split– New Nuclear

Membrane forms

• At this point, each cell has 46 chromosomes

• 2n

Prophase II

• In Prophase II:

• These cells go straight from telophase I to prophase II. They skip interphase.

• NO CELL CYCLE

Metaphase II

• In Metaphase II:– Chromosomes line

up along midline of cell

Anaphase II

• In Anaphase II:– CHROMATIDS

separate• Just like Mitosis

Telophase II

• In Telophase II:– Nuclear Membrane

begins to form– Each cell has 23

chromosomes– 1n

Review of the difference between Mitosis and Meiosis

OogenesisOogenesisOccurs in the Occurs in the ovariesovariesTwo divisions produce Two divisions produce 3 polar 3 polar

bodiesbodies that die and that die and 1 egg1 eggPolar bodies die because of Polar bodies die because of

unequal division of cytoplasmunequal division of cytoplasmImmature egg called Immature egg called oocyteoocyteStarting at puberty, one Starting at puberty, one

oocyte matures into an oocyte matures into an ovum ovum (egg)(egg) every 28 days every 28 days

SpermatogenesisSpermatogenesis

Occurs in the Occurs in the testestestes

Two divisions Two divisions produce 4 produce 4 spermatidsspermatids

Spermatids Spermatids mature into mature into spermsperm

Men produce Men produce about about 250,000,000 250,000,000 sperm per sperm per dayday

Questions

• What kind of cells are we creating during meiosis?

• How many chromosomes do they end up with?

• How many chromosomes do cells end with in mitosis?