Cell Division

Cell division – parent cell divides into 2

daughter cells

2 types of cell division:

1) mitosis – division of somatic (body) cell

to produce identical somatic cells

-occurs in a series of phases

Interphase

• part of cell cycle when cell is not dividing

• DNA replication occurs during this time as

well as all other cell activities

*includes G1, S, and G2

Prophase

• first phase of mitosis• chromatid pairs shorten, thicken, become

visible• centrioles move to opposite poles• spindle fibers form (between centrioles)• nuclear membrane, nucleolus disappear

*Plant cells have no centrioles, but spindle

still forms

Metaphase

• chromatid pairs line up along middle of spindle (equator)

• spindle fibers attach to centromere of each chromatid pair

Anaphase

• chromatid pairs move to opposite poles of the spindle

• separation of chromatid pairs signals the start of anaphase

Telophase

• final phase of mitosis

• begins when chromosomes arrive at poles

• chromosomes get longer, thinner

• spindle breaks down

• nuclear membrane forms around each set

of chromosomes, nucleolus reappears

• cell begins to divide in two

Telophase

• cytokinesis – division of cytoplasm

Plant cell vs. Animal cell cytokinesis:

Plant – Animal -

cell plate forms, membrane pinches

elongates, forming inward & forms a

new cell wall depression or cell

furrow

Meiosis

• Interphase – DNA replication

• Prophase I – homologous chromosomes pair up & form 4-stranded groups called tetrads

-chromosomes enlarge, exchange corresponding segments of DNA (crossing over)

Meiosis

• chromosomes shorten, thicken, become visible

• spindle forms, nuclear membrane & nucleolus break down

Metaphase I – tetrads move toward middle of spindle & line up along equator

-spindle fibers attach to centromeres

MeiosisAnaphase I – chromatid pairs forming each

tetrad move to opposite poles

Telophase I – nuclear membrane reappears

-cytoplasm begins to divide & form either cell plate or cell furrow

(This first division is the reduction division)

Meiotic Interphase – NO DNA replication

Meiosis

Prophase II - chromatid pairs shorten/thicken

-no tetrads (since they already separated in

the first division)

-spindle begins to form; nuclear membrane breaks down

MeiosisMetaphase II – paired chromatids line up at the

equator; spindle fibers attach to centromeres of each chromatid

Anaphase II – members of each chromatid pair move apart to opposite poles

Telophase II – nuclear membrane reappears; cytokinesis occurs; chromosomes become long, thin

Meiosis

• 4 haploid cells result

(gametogenesis)

Spermatogenesis – formation of sperm

-4 evenly sized cells

Oogenesis – formation of egg cells

-1 egg & 3 small polar bodies