Name: ________________________________________
Period: ___________ Date: __________________
Meiosis Notes
Meiosis & Sexual Reproduction
 In sexual reproduction two cells, one from each parent, combine to form an offspring.
 Human body cells contain 46 chromosomes. (the full number for humans)
Gametes
 Cells that contain half the usual number of chromosomes.
 One chromosome from each pair.
 Humans gametes contain 23 chromosomes
 Female gamete = egg cells
 Male gamete = sperm cells
Fertilization
 Takes place when a sperm and egg combine to form one cell
 23 + 23 = 46 for humans
Meiosis
 A special kind of cell division that produces haploid cells
 During meiosis, a single cell goes through two cell divisions
 Meiosis I and Meiosis II
 Location: reproductive tissue/organs/system only
Beginning Meiosis
 Before meiosis begins, the chromosomes of the parent cell are copied (like in mitosis) during
interphase.
 It will have twice as many as usual
 92 chromosomes (46 pairs)
 At the beginning of Meiosis I, the cell has two copies of each chromosome that are attached to each
other
 During Meiosis II, each of the two cells divide again producing four haploid cells, each with one
unpaired set of chromosomes
Meiosis I
1. Prophase I
 Chromosomes condense and the nuclear membrane disappears
2. Metaphase I
 Chromatids arrange as pairs in the middle of the cell
3. Anaphase I
 One of each chromatid pair separate and are pulled to opposite ends of the cell
4. Telophase I
 The cell divides into two cells
Meiosis II
 Before Meiosis II, there is no doubling of the chromosomes*
Prophase II
 Chromosomes condense and the nuclear membrane disappears
Metaphase II
 Each chromosome lines up in the middle of the cell
 Not in pairs
Anaphase II
 The chromatids split forming individual chromosomes
 The separate chromosomes are pulled to the opposite ends of the cell
Telophase II & Cytokinesis
 Both cells divide
 Produces 4 cells (either egg or sperm)
 NOT identical
Mitosis vs Meiosis
Type of Cell
Number of divisions
Parent vs. Daughter
Mitosis
Meiosis
Body Cells and Diploid
Sex Cells – egg and sperm,
also known as Gametes,
Haploid
1
(4 steps)
2 (8 steps)
Identical to each other
Not identical to each other
46 (23 pairs)
23 (not in pairs)
(original cell vs. resulting
cells)
Number of chromosomes
(human)