Unit 7: Cellular ReproductionCh. 22: Cell Reproduction

22:1 Mitosis & 22:2 Meiosis

Body (somatic) cells divide

Formation of sex cells (gametes)

Diploid = 2nDiploid = 2n

2n

haploid = n

2n 2n

n n n n

Meiosis 1

Meiosis 2

n nhaploid = n

200

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

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.

What are the 2 Types of Cellular Reproduction in Eukaryotes?

mitosis• 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

meiosis• 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

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

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)

Cellular Reproduction: Mitosis & Meiosis

body (somatic) cells divide

formation of sex cells (gametes)

diploid2n = 4

diploid2n = 4

2n = 4(double stranded)

haploidn = 2

2n = 4 (single stranded) n = 2

Meiosis 1

Meiosis 2

n = 2 (double stranded)

haploid

n = 2

2n = 4(double stranded)

2n = 4 (single stranded)

n = 2(double stranded)

(single stranded)

n = 2 n = 2 n = 2

Mitosis (Ch. 22:1)

The Cell Cycle Has 3 Main PhasesA. Interphase

B. Mitosis– has 4 parts

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

C. Cytokinesis

• I Pee MATt, C?

Which takes longer, interphase or 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 (in animal cells only)

A. Before Mitosis: Interphase

• What happens during 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.

Spindle fibers

centrioles

B. Mitosis (Prophase—Step 1)Spindle fibersSpindle fibers

centriolesSpindle fibersSpindle fibers

centriolesSpindle fibersSpindle fibers

centriolesSpindle fibers

Spindle fibers

centriolescentriolescentriolescentrioles

• What happens during metaphase?

a. Chromosomes line up at middle (equator) of cell.

b. Chromosomes attach to spindle fibers by centromeres.

B. Mitosis (Metaphase—Step 2)

• 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).

B. Mitosis (Anaphase—Step 3)

• 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• cleavage furrow forms (animal)• cell plate forms (plant)

B. Mitosis (Telophase—Step 4)

• 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

C. After Mitosis: Cytokinesis

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

cell & each other

So, What is the End Result of Mitosis?

Mitosis Animationshttp://www.sumanasinc.com/webcontent/animations/content/mitosis.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.htmlhttp://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swfhttp://www.teachersdomain.org/asset/tdc02_vid_dnadivide/

1

2

3

4

5

What stage of the cell cycle is represented by each number?

Interphase

Cytokinesis

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

What are the 2 Types of Cellular Reproduction in Eukaryotes?

mitosis• 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

meiosis• 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

Cellular Reproduction: Mitosis & Meiosis

body (somatic) cells divide

formation of sex cells (gametes)

diploid2n = 4

diploid2n = 4

2n = 4(double stranded)

haploidn = 2

2n = 4 (single stranded) n = 2

Meiosis 1

Meiosis 2

n = 2 (double stranded)

haploid

n = 2

2n = 4(double stranded)

2n = 4 (single stranded)

n = 2(double stranded)

(single stranded)

n = 2 n = 2 n = 2

Meiosis: The Production of Gametes (22:2)

• What would happen if the # of chromosomes wasn’t 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

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

2n = diploid

n = haploid

gametes

MeiosisA. Interphase

B. Meiosis 1 (separation of homologous chromosomes)

– has 4 parts

1. Prophase 1

2. Metaphase 1

3. Anaphase 1

4. Telophase 1

C. Cytokinesis 1

D. Meiosis 2 (separation of sister chromatids… essentially mitosis)

– has 4 parts

1. Prophase 2

2. Metaphase 2

3. Anaphase 2

4. Telophase 2

E. Cytokinesis 2

traits.

Different versions of a gene for the same trait are called “alleles”.

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).

B. Meiosis 1 (Prophase 1—Step 1) • 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 (double file) @ the middle (equator).• Can have different arrangements (due to

independent assortment).– What does this cause?

» genetic variability2n

B. Meiosis 1 (Metaphase 1—Step 2)

• What happens during anaphase 1?

a. Tetrads (pairs of double-stranded homologous chromosomes) separate.

b. move towards opposite poles

2n

B. Meiosis 1 (Anaphase 1—Step 3)

• 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.

c. Chromosomes unravel back into chromatin form.

d. Nucleoli reappear.

e. Cytokinesis 1 starts.

n

n

B. Meiosis 1 (Telophase 1—Step 4)

• 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.

C. After Meiosis 1: Cytokinesis 1

• Replication does NOT occur again before meiosis 2.– Daughter cells

from meiosis 1 stay haploid.

• Meiosis 2 happens in both daughter cells.

Moving From Meiosis 1 to Meiosis 2…

• 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

D. Meiosis 2 (Prophase 2—Step 1)

• What happens during metaphase 2?a. Spindle fibers attach to chromosomes at

centromere.

b. Double-stranded chromosomes line up (single file) @ equator• so 1 sister chromatid is on each side of equator.

n

n

D. Meiosis 2 (Metaphase 2—Step 2)

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

D. Meiosis 2 (Anaphase 2—Step 3)

• 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.

D. Meiosis 2 (Telophase 2—Step 4)

• 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

E. After Meiosis 2: Cytokinesis 2

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.

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

spermatogenesis

oogenesis

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)

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

2n = diploid

n = haploid

gametes

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.php

• meiosis– http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

– http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf

– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html

– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

• comparison mitosis & meiosis– http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/

animation__comparison_of_meiosis_and_mitosis__quiz_1_.html

– http://www.pbs.org/wgbh/nova/miracle/divi_flash.html