1. Quick Review Diploid Haploid diploid haploid 23
What terms are used to describe cells containing the normal number of chromosomes?
What terms are used to describe cells containing half the number of chromosomes?
Mitosis produces ________ cells.
Meiosis produces ________ cells.
How many pairs of chromosomes do human body cells have? ___ pairs
Diploid
Haploid
diploid
haploid 23

2. Chromosome Numbers of Some Common Organisms
Body Cell (2n)
Gamete (n)
Human 46
Garden Pea 7
Fruit Fly 8
Tomato 12
Dog 78
Chimpanzee 24
Leopard Frog 26
Corn 10
Apple 17
Indian Fern
1260 23 14 4 24 39 48 13 20 34
630

3. Meiosis I
During prophase I, the ____________ coil up and the ______ fibers form. Then each pair of homologous chromosomes come together to form a four-part structure called a _____ (tetra = what number? __). A tetrad consists of two homologous chromosomes, each made up of two sister chromatids. These 4 chromatids in a ______ are held very close and tightly together. In fact, they are so close that the arms of non-sister chromatids can wind and twist around each other, and exchange genetic information. This is called ________ ____. Crossing over results in new combinations of alleles.
chromosomes
spindle
tetrad 4
tetrad
crossing
over

4. The Phases of MEIOSIS Before meiosis begins: Interphase
Before meiosis begins, what must happen to the cell’s DNA/ chromosomes?____________________________
Meiosis occurs in sexual reproduction when 1 diploid germ cell produces 4 haploid cells that can mature to become _______ (sperm or ova).
They must be copied/ duplicated
gametes

5. Prophase I Like prophase of mitosis: The ______ ________ disappears.
________ move to the opposite poles and the _____ _____ form between the centrioles.
_________ condenses into sister _________
nuclear membrane
Centrioles
spindle fibers
Chromatin
chromatids
Unlike prophase of mitosis:
Pairs of homologous chromosomes form ______
______ _____ may occur.
tetrads
Crossing over

6. Metaphase I
Spindle fibers attach to the ____________________.
Tetrads line up at the _________ plate.
kinetochore or centromere
metaphase
Anaphase I
Tetrads, which consist of two _________ __________, separate.
homologous chromosomes

7. Telophase I / Cytokinesis I
______ _______ reappears.
______ ____ disappears.
__________, the division of the cytoplasm and the organelles begins and ends forming two cells.
Nuclear envelope
Spindle fiber
Cytokinesis

8. Meiosis II
The purpose of meiosis II is to separate _______ ________ of each chromosome into separate cells.
sister chromatids
Prophase II
The _____ _________ disappears.
______ ______ form.
________ condenses into sister _________
nuclear membrane
Spindle fibers
Chromatin
chromatids

9. Metaphase II Sister chromatids attach to the ______ ____
Sister chromatids line up at the _________ plate.
spindle fibers
metaphase

10. Anaphase II Sister chromatids separate into ___________.
Chromosomes move to the opposite _____.
chromosomes
poles

11. Telophase II ______ _______ reforms. 4 _______ are formed.
Nuclear envelope
gametes