I. ChromosomesA. composed of chromatin –

a complex of DNA and proteins

B. Homologous chromosomes: pairs that contain the same genes, one from each parent

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Homologous pair

karyotype

C. Chromosomes must be replicated before cell division.

1. sister chromatids: 2 copies of the same chromosome

2. connected to each other at their kinetochores

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II. Why do cells divide?A. Replacement - cells wear

out & dieB. Repair - tissues can be

damaged by injury or infection

C. Growth of the organismD.Reproduction

III. MitosisA. New cells are identical

to the old cells B. Chromosome number is

the same in parent & daughter cells (diploid – 2N)

C. Growth, repair, & asexual reproduction

MITOSIS

IV.Phases of MitosisA. Interphase

1. Growth & normal cell activities

2. DNA is duplicated

B.Prophase1.Chromosomes

condense (sister chromatids)

2.Centrioles move to poles

3.Nuclear membrane dissolves

C.Metaphase1.Sister

chromatids line up along equator of cell

2.Chromosomes attach to spindle fibers

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D.Anaphase1.Spindle fibers pull

sister chromatids to opposite ends of cell

**an identical set of chromosomes moves to each pole

E.Telophase1.Chromosomes

uncoil2.Nucleus reforms3.Cytokinesis: cell

membrane pinches in to form 2 separate cells

B.Meiosis1.Parent cell divides twice to

produce 4 cells2.Produces gametes (sex

cells)3.Daughter cells have half

the original number of chromosomes (haploid -1N)

MEIOSIS

4.When two gametes join to form a zygote, it will have the normal # of chromosomes

5.Daughter cells are not genetically identical:

a)Homologous chromosomes separate, sending one version of each to the new cells

b)crossing over: sometimes chromosomal segments are exchanged between homologous chromosomes

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V. Phases of MeiosisA. During meiosis I, homologous

chromosomes are held together by proteins

1. Interphase I2. Prophase I3. Metaphase I:line up next

homologous partner4. Anaphase I: homologous

pairs separate, sister chromatids remain together

5. Telophase I

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Meiosis I: (Reduction division)

B. Meiosis II1. Prophase II2. Metaphase II3. Anaphase II: sister

chromatids separate4. Telophase II

Meiosis II: (Mitotic division)