Quick Review

1. What terms are used to describe cells containing the normal number of chromosomes?

2. What terms are used to describe cells containing half the number of chromosomes?

3. Mitosis produces ________ cells.

4. Meiosis produces ________ cells.

5. How many pairs of chromosomes do human body cells have? ___ pairs

Diploid

Haploid

haploiddiploid

23

Chromosome Numbers of Some Common Organisms

Organism 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

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

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

Prophase I

1. The ______ ________ disappears.

2. ________ move to the opposite poles and the _____ _____ form between the centrioles.

3. _________ condenses into sister _________

Like prophase of mitosis:

Unlike prophase of mitosis:

1. Pairs of homologous chromosomes form ______

2. ______ _____ may occur.

nuclear membrane

Centriolesspindle fibers

Chromatinchromatids

tetradsCrossing over

Metaphase I

1. Spindle fibers attach to the ____________________.

2. Tetrads line up at the _________ plate.

Anaphase I1. Tetrads, which consist of two

_________ __________, separate.

kinetochore or centromeremetaphase

homologous chromosomes

Telophase I / Cytokinesis I

1. ______ _______ reappears.

2. ______ ____ disappears.

3. __________, the division of the cytoplasm and the organelles begins and ends forming two cells.

Nuclear envelopeSpindle fiberCytokinesis

Meiosis II

The purpose of meiosis II is to separate _______ ________ of each chromosome into separate cells.

Prophase II

sister chromatids

1. The _____ _________ disappears.

2. ______ ______ form.

3. ________ condenses into sister _________

nuclear membraneSpindle fibers

Chromatinchromatids

Metaphase II

1. Sister chromatids attach to the ______ ____

2. Sister chromatids line up at the _________ plate.

spindle fibers

metaphase

Anaphase II

1. Sister chromatids separate into ___________.

2. Chromosomes move to the opposite _____.

chromosomes

poles

Telophase II

1. ______ _______ reforms.

2. 4 _______ are formed.

Nuclear envelopegametes