Ch. 22: Cell Reproduction
22:1 Mitosis & 22:2 Meiosis
Diploid = 2n
Body
(somatic) cells divide
Diploid = 2n
Formation of sex cells
(gametes)
2n
2n
2n n n
Meiosis 1 haploid = n
Meiosis 2 n haploid = n n n n

• 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

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

• What does it mean when a cell is “haploid”?
– cell contains one of each 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)

mitosis
• occurs in all body meiosis
• occurs in (germ) cells cells of reproductive organs
• cell divides once
– results in:
• 2 diploid cells
– with same # of chromosomes
(as parent cell)
» 46 (humans)
– function:
• growth
• repair
– ovaries & testes
• cell divides twice
– results in:
• 4 haploid cells
– with ½ # of chromosomes
(as parent cell)
» 23 (humans)
– function:
• makes sperm & eggs for sexual reproduction
– promotes variation

Cellular Reproduction: Mitosis & Meiosis
Diploid = 2n
Body
(somatic) cells divide
Diploid = 2n
Formation of sex cells
(gametes)
2n
2n
2n n
Meiosis 1 haploid = n
Meiosis 2 n n n haploid = n n n

A. I
– has 4 parts
1. P rophase
2. M etaphase
3. A naphase
4. T elophase
C. C
Which takes
I p
m
a
t
c longer,
mitosis?

• 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

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

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

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

• What happens during telophase?
a. Chromosomes gather at opposite ends of “cells”.
b. Nuclear membrane reforms
• forming 2 new nuclei.
c. Chromosomes unravel back into chromatin form.
d. Nucleoli reappear e. Cytokinesis begins
• as cleavage furrow forms.

• 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
– and have 2 of each chromosome.

2
1
What stage of the cell cycle is represented by each number?
4
5
3
Mitosis Animations http://www.sumanasinc.com/webcontent/animations/content/mitosis.html
http://highered.mcgrawhill.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/

Interphase
Cytokinesis
Cytoplasm divides forming 2 daughter cells that are identical to the parent cell & each other

• Where does meiosis occur?
– In germ cells of ovaries & testes.
• What does meiosis produce?
– gametes (sperm & eggs) with ½ original # of chromosomes
• What would happen if the # of chromosomes wasn’t 1/2?
– After fertilization there would be 2x the # of chromosomes
2n = diploid
n = haploid gametes
Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid #

Cellular Reproduction: Mitosis & Meiosis
Body
(somatic) cells divide
2n
Diploid = 2n
Formation of sex cells
(gametes)
2n
2n
Diploid = 2n
2n
Meiosis 1 n
Meiosis 2 n n n haploid = n n n

A. I nterphase
B. Meiosis 1
(separation of homologous chromosomes )
– has 4 parts
1. P rophase 1
2. M etaphase 1
3. A naphase 1
4. T elophase 1
C. C ytokinesis 1
D. Meiosis 2
(separation of sister chromatids… essentially mitosis)
–has 4 parts
1. P rophase 2
2. M etaphase 2
3. A naphase 2
4. T elophase 2
E. C ytokinesis 2

traits.

• To summarize…
– 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.

• 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).

• What happens during prophase 1?
a. Nucleolus & nuclear membrane disintegrates.
b. (In animals) centrioles move to opposite poles.
c. Spindle fibers form, connecting centrioles.
d. Homologous chromosomes join
( synapsis ), forming tetrads ( 4 chromatids).
• genes may swap ( crossing over )
2n

• What happens during metaphase 1?
a. Spindle fibers attach to chromosomes.
b. Tetrads line up @ the middle (equator).
• Can have different arrangements (due to independent assortment).
– What does this cause?
» genetic variability
2n

• What happens during anaphase 1?
a.
Tetrads (pairs of double-stranded homologous chromosomes) separate.
b.
move towards opposite poles
2n

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

• 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.

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.

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

• What happens during metaphase 2?
a. Spindle fibers attach to chromosomes at centromere.
n b. Double-stranded chromosomes line up @ equator
• so 1 sister chromatid is on each side of equator.
n n n n

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

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

E. After Meiosis 2: Cytokinesis 2
• When does cytokinesis 2 start?
– During telophase 2 n
• 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

• 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 ova (egg)
• other 3 daughter cells are small, nonfunctional polar bodies

• 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)
2n = diploid
n = haploid gametes
Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid #

• 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.

• 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.php
• meiosis
– http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
– http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf
– http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html
– http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html
• comparison mitosis & meiosis
– http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__comparison_of_meiosis_an d_mitosis__quiz_1_.html
– http://www.pbs.org/wgbh/nova/miracle/divi_flash.html