Unit 7: Cellular Reproduction

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Unit 7 Cellular Reproduction
200

• Ch. 22 Cell Reproduction
• 221 Mitosis 222 Meiosis

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Recall

• Why are cells small?
• to keep surface area to volume ratio high
• How do cells stay small?
• by dividing
• What must happen before a cell divides? Why?
• DNA is replicated so each new cell gets a copy
• Why else do cells divide?
• growth (increase of cells)
• repair damage
• replace old/worn out cells

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Cell Reproduction in Prokaryotes

• Prokaryotes have a single, circular chromosome.
• Cell reproduction is by binary fission.
• chromosome duplicates
• cell divides in ½.
• Each daughter cell is genetically identical to
  each other as well as parent cell.

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What are the 2 Types of Cellular Reproduction in
Eukaryotes?

• mitosis

• meiosis

• occurs in all body (somatic) cells
• cell divides once
• results in
• 2 diploid cells
• with same of chromosomes (as parent cell)
• 46 (23 pairs) (humans)
• function
• growth
• repair

• occurs in (germ) cells of reproductive organs
• ovaries testes
• cell divides twice
• results in
• 4 haploid cells
• with ½ of chromosomes (as parent cell)
• 23 (humans)
• function
• makes gametes (sperm eggs) for sex. reprod.
• promotes variation

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Diploid Haploid Cells

• What does it mean when a cell is diploid?
• cell contains two of each (type of) chromosome
• thus 2 sets of genes
• 1 from each parent
• How do we indicate that a cell is diploid?
• represented by 2n
• ex. humans ? 2n 46
• What types of cells are diploid?
• ex. somatic (body) cells

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Diploid Haploid Cells

• What does it mean when a cell is haploid?
• cell contains one of each (type of) chromosome
• thus 1 set of genes
• ½ the original number
• How do we indicate that a cell is haploid?
• represented by n
• ex. humans ? n 23
• What types of cells are haploid?
• ex. gametes (sperm/eggs)

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Cellular Reproduction Mitosis Meiosis
2n 4 (double stranded)
n 2 (double stranded)
(single stranded)
2n 4 (single stranded)
n 2
n 2
n 2
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Mitosis (Ch. 221)
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The Cell Cycle Has 3 Main Phases

• Interphase
• Mitosis
• has 4 parts
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• I Pee MATt, C?

Which takes longer, interphase or mitosis?
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A. Before Mitosis Interphase

• What is happening in the cell?
• life functions are being carried out
• DNA is in the form of...?
• chromatin
• What happens before mitosis begins?
• DNA replicates
• forming 2 strands called sister chromatids
• held together by centromere
• centrioles duplicate (in animal cells only)

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B. Mitosis (ProphaseStep 1)
spindle fibers
centrioles

• What happens during prophase?
• Double-stranded chromosomes become clearly
  visible.
• Nucleolus nuclear membrane disintegrate.
• (In animals) centrioles move to opposite poles
  (ends).
• Spindle fibers form connecting centrioles.

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B. Mitosis (MetaphaseStep 2)

• What happens during metaphase?
• Chromosomes line up single-file at middle
  (equator) of cell.
• Chromosomes attach to spindle fibers by
  centromeres.

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B. Mitosis (AnaphaseStep 3)

• What happens during anaphase?
• Centromeres divide.
• Sister chromatids are pulled apart (_at_ centromere)
• forming single-stranded chromosomes
• Chromosomes move toward opposite poles (away from
  middle).

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B. Mitosis (TelophaseStep 4)

• What happens during telophase?
• Chromosomes gather at opposite ends of cells.
• Nuclear membrane reforms
• forming 2 new nuclei
• Chromosomes unravel back into chromatin form.
• Nucleoli reappear
• Cytokinesis begins
• cleavage furrow forms (animal)
• cell plate forms (plant)

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C. After Mitosis Cytokinesis

• When does cytokinesis start?
• during telophase (but cytokinesis is not a phase
  of mitosis)
• What happens during cytokinesis?
• Cytoplasm is divided
• by cleavage furrow in animal cells
• by cell plate in plant cells
• which becomes new cell wall
• 2 new diploid cells are formed
• have 2 of each chromosome

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So, What is the End Result of Mitosis?

• The DNA that was duplicated during interphase is
  equally divided into 2 new diploid daughter cells
• same DNA as parent cell each other

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Mitosis Animations http//www.sumanasinc.com/webco
ntent/animations/content/mitosis.html http//highe
red.mcgraw-hill.com/sites/0072495855/student_view0
/chapter2/animation__mitosis_and_cytokinesis.html
http//www.stolaf.edu/people/giannini/flashanimat/
celldivision/crome3.swf http//www.teachersdomain.
org/asset/tdc02_vid_dnadivide/
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What are the 2 Types of Cellular Reproduction in
Eukaryotes?

• mitosis

• meiosis

• occurs in all body (somatic) cells
• cell divides once
• results in
• 2 diploid cells
• with same of chromosomes (as parent cell)
• 46 (23 pairs) (humans)
• function
• growth
• repair

• occurs in (germ) cells of reproductive organs
• ovaries testes
• cell divides twice
• results in
• 4 haploid cells
• with ½ of chromosomes (as parent cell)
• 23 (humans)
• function
• makes gametes (sperm eggs) for sex. reprod.
• promotes variation

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Cellular Reproduction Mitosis Meiosis
2n 4 (double stranded)
n 2 (double stranded)
(single stranded)
2n 4 (single stranded)
n 2
n 2
n 2
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Meiosis The Production of Gametes (222)

• What would happen if the of chromosomes wasnt
  reduced by ½ during meiosis?
• After fertilization there would be 2x the of
  chromosomes
• How does meiosis promote genetic variation?
• mixing DNA from 2 different parents

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Meiosis

• Interphase
• Meiosis 1 (separation of homologous chromosomes)
• has 4 parts
• Prophase 1
• Metaphase 1
• Anaphase 1
• Telophase 1
• Cytokinesis 1

• Meiosis 2 (separation of sister chromatids
  essentially mitosis)
• has 4 parts
• Prophase 2
• Metaphase 2
• Anaphase 2
• Telophase 2
• Cytokinesis 2

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A. Before Meiosis Interphase

• What happens during interphase?
• Cell is diploid (has 2 of each chromosome)
• DNA replicates forming double-stranded
  chromosomes.
• But, the cell is still diploid (2n).

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B. Meiosis 1 (Prophase 1Step 1)

• What happens during prophase 1?
• Nucleolus nuclear membrane disintegrates.
• (In animals) centrioles move to opposite poles.
• Spindle fibers form, connecting centrioles.
• Homologous chromosomes join (synapsis), forming
  tetrads (4 chromatids).
• genes may swap (crossing over)

2n
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B. Meiosis 1 (Metaphase 1Step 2)

• What happens during metaphase 1?
• Spindle fibers attach to chromosomes.
• Tetrads line up (double file) _at_ the middle
  (equator).
• Can have different arrangements (due to
  independent assortment).
• What does this cause?
• genetic variability

2n
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B. Meiosis 1 (Anaphase 1Step 3)

• What happens during anaphase 1?
• Tetrads (pairs of double-stranded homologous
  chromosomes) separate.
• move towards opposite poles

2n
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B. Meiosis 1 (Telophase 1Step 4)

• What happens during telophase 1?
• Chromosomes gather at opposite ends.
• Nuclear membrane reforms around each cluster of
  chromosomes
• forming 2 new haploid (n) nuclei
• with 1 of each double-stranded chromosome.
• Chromosomes unravel back into chromatin form.
• Nucleoli reappear.
• Cytokinesis 1 starts.

n
n
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C. After Meiosis 1 Cytokinesis 1

• When does cytokinesis 1 start?
• during telophase 1 (but is not a phase of
  meiosis)
• What happens during cytokinesis 1?
• Cytoplasm is divided
• by cleavage furrow in animal cells.
• by cell plate in plant cells
• which becomes new cell wall.
• 2 new haploid cells are formed
• with 1 of each chromosome.

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Moving From Meiosis 1 to Meiosis 2

• Replication does NOT occur again before meiosis
  2.
• Daughter cells from meiosis 1 stay haploid.
• Meiosis 2 happens in both daughter cells.

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D. Meiosis 2 (Prophase 2Step 1)

• What happens during prophase 2?
• Nucleolus nuclear membrane disintegrate.
• (In animals) centrioles move to opposite poles.
• Spindle fibers form, connecting centrioles.

n
n
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D. Meiosis 2 (Metaphase 2Step 2)

• What happens during metaphase 2?
• Spindle fibers attach to chromosomes at
  centromere.
• Double-stranded chromosomes line up (single file)
  _at_ equator
• so 1 sister chromatid is on each side of equator.

n
n
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D. Meiosis 2 (Anaphase 2Step 3)

• What happens during anaphase 2?
• Sister chromatids separate (at centromere)
• forming single-stranded chromosomes.
• move towards opposite poles

n
n
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D. Meiosis 2 (Telophase 2Step 4)

• What happens during telophase 2?
• Chromosomes gather at opposite ends.
• Nuclear membrane reforms around each cluster of
  chromosomes
• forming 4 new haploid (n) nuclei
• with 1 of each single-stranded chromosome.
• Chromosomes unravel back into chromatin form.
• Nucleoli reappear.
• Cytokinesis 2 starts.

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E. After Meiosis 2 Cytokinesis 2

• When does cytokinesis 2 start?
• during telophase 2
• What happens during cytokinesis 2?
• cytoplasm is divided
• by cleavage furrow in animal cells.
• by cell plate in plant cells
• which becomes new cell wall.
• What does each new cell end up with?
• combo of chromosomes from mom dad
• Only one chromosome from each homologous pair

n
n
n
n
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To summarize

• Meiosis Has 2 Stages (Divisions)
• Meiosis 1
• Homologous chromosomes are separated, but are
  still double stranded.
• Cells become haploid.
• Meiosis 2
• Sister chromatids are separated.
• Still haploid, but now have single strands.

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End Result of Meiosis

• What is the result of meiosis in males?
• spermatogenesis (formation of sperm)
• all 4 daughter cells become sperm
• What is the result of meiosis in females?
• Oogenesis (formation of eggs)
• only 1 daughter cell becomes ovum (egg)
• other 3 daughter cells are small, nonfunctional
  polar bodies

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spermatogenesis
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oogenesis
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Fertilization

• What is fertilization?
• the fusion of sperm egg
• What is formed by fertilization?
• a zygote (which will develop into a baby)
• What happens to the chromosome after
  fertilization?
• diploid number restored (zygote has 2 of each
  chromosome)

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Review Animations

• mitosis
• http//www.biology.arizona.edu/cell_bio/tutorials/
  cell_cycle/cells3.html
• http//www.johnkyrk.com/mitosis.html
• http//www.accessexcellence.org/RC/VL/GG/mitosis.p
  hp
• meiosis
• http//www.sumanasinc.com/webcontent/animations/co
  ntent/meiosis.html
• http//www.stolaf.edu/people/giannini/flashanimat/
  celldivision/meiosis.swf
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter28/animation__stages_of_meiosi
  s.html
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter28/animation__how_meiosis_work
  s.html
• comparison mitosis meiosis
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__comparison_of_mei
  osis_and_mitosis__quiz_1_.html
• http//www.pbs.org/wgbh/nova/miracle/divi_flash.ht
  ml