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Cellular ReproductionCell divisionFunctions of cell division: *reproduction *growth and development *repair

Cellular ReproductionIn asexual reproduction:•Single-celled organisms reproduce by simple cell division •There is no fertilization of an egg by a sperm

Asexual ReproductionFUNCTIONS OF CELL DIVISION

Sea stars

LM

Amoeba African Violet

Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

Cellular Reproduction

Eukaryotic Chromosomes

Chromosomes

LM

Duplicated chromosomes(sister chromatids) TE

M

Tight helical fiber

Looped domainsTE

M

Centromere

Nucleosome

“Beads ona string”

HistonesDNA double helix

Eukaryotic Chromosomes–The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding.

–Histones are proteins used to package DNA in eukaryotes.

–Nucleosomes consist of DNA wound around histone molecules.

Chromosome Structure

Chromosome

Centromere

Sister Chromatids

The Cell Cycle• The cell cycle consists

of two distinct phases

Interphase Mitotic phase

S phase(DNA synthesis;

chromosome duplication)

Interphase(90% of time)G1

Mitoticphase (M)

(10% of time)

Cytokinesis Mitosis

G2

• G1: Metabolism and growth• End of G1: Cell signaled to

divide• S (synthesis): DNA is

duplicated • G2: Cell forms chromosomes,

completes preparations for cell and nuclear division

Interphase

Interphase

Nuclearenvelope

LM

Plasmamembrane

Centrosomes (with centriole pairs)

Chromatin

INTERPHASE

Prophase

Chromosome, consistingof two sister chromatids

Spindle microtubules

Fragments of nuclear envelopeCentrosome

Centromere

Early mitotic spindle

PROPHASE

Figure 8.7.a

Metaphase, Anaphase, TelophaseANAPHASEMETAPHASE TELOPHASE

Spindle Daughterchromosomes

Cleavagefurrow

Nuclearenvelopeforming

CytokinesisAnimal cells Plant cells

Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

Meiosis

Meiosis

MEIOSIS I

Sisterchromatidsseparate.

MEIOSIS II

Homologouschromosomesseparate.

INTERPHASE BEFORE MEIOSIS

Sisterchromatids

Duplicated pair ofhomologouschromosomes

Chromosomesduplicate.

Pair of homologouschromosomes indiploid parent cell

MeiosisMEIOSIS I:

Sister chromatidsremain attached

Pair ofhomologouschromosomes

INTERPHASE

Sisterchromatids

Homologouschromosomespair up andexchangesegments.

Chromosomesduplicate.

Pairs of homologouschromosomesline up.

Pairs of homologouschromosomessplit up.

Nuclearenvelope

Chromatin

Centromere

Microtubulesattachedto chromosome

Sites of crossing over

Spindle

Centrosomes (with centriolepairs)

PROPHASE I METAPHASE I ANAPHASE I

TELOPHASE II AND

CYTOKINESIS

Sister chromatidsseparate

ANAPHASE II

Cleavagefurrow

TELOPHASE I AND

CYTOKINESIS

Two haploidcells form;chromosomesare stilldoubled.

MEIOSIS II: SISTER CHROMATIDS SEPARATEPROPHASE II METAPHASE II

During another round of cell division, the sisterchromatids finally separate; four haploiddaughter cells result, containing single

chromosomes.

Haploid daughtercells forming

Meiosis

MeiosisHow do we account for genetic variation?

*Independent assortment *Crossing over *Random fertilization

Independent Assortment:

Cross over:

Mitosis and Meiosis