Chapter 15 Mitosis And Meiosis

Front 1

Eukaryotic Cell Cycle

Back 1

"Omnis cellula e cellula" means Every cell originates from another cell

* Highly regulated series of events that leads to cell division*

*All organisms produced by series of repeated rounds of Cell Growth and Division extending back to nearly 4 billion years ago*

Cell Division via Mitosis and Meiosis

Front 2

Mitosis

Back 2

Two daughter cell with the same amount of Genetic material as mother cell

Front 3

Meiosis

Back 3

Daughter cells with a single set of Chromosomes

Where sexual reproduction happens

Front 4

Eukaryotic Chromosomes

Back 4

The chromosomes become compact enough to be seen with a light microscope, when cells get ready to divide

Front 5

Cytogenetics

Back 5

Field of Genetics involving microscopic examination of chromosomes and cell division

Front 6

Karyotype

Back 6

Reveals number, size, and form of chromosomes in an actively dividing cell

Front 7

Sets of Chromosomes

Back 7

**Humans have 23 pairs of chromosomes**

(46 total chromosomes)

- Autosomes- 22 pairs in humans

- Sex chromosomes- 1 pair in humans * XX= Female or XY= Male

Front 8

Ploidy

Back 8

Diploid or 2n- Humans have 23 pairs of chromosomes (one from mother, one from father)

Haploid or n- Gametes have 1 member of each pair of chromosomes or 23 total chromosomes

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Homologues

Back 9

*In diploid species, members of a pair of chromosomes - similar

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Autosomes

Back 10

Each Homologue identical in size and genetic composition

EX: Both carry gene for eye color but one may have brown and the other blue

* Slight difference in sequence can provide large variation in gene function

Front 11

Sex Chromosomes

Back 11

X and Y very different from each other in size and composition

Front 12

Cell Cycle

Back 12

Growth, replication, division to produce new

cells

M- Mitosis and Cytokinesis

G0- Substitutes for G1 for cells postponing division or never dividing again

Front 13

Interphase Phase Includes

Back 13

G1- 1st Gap

S- Synthesis of DNA

G2- 2nd Gap

Front 14

G0 Phase

Back 14

Nondividing Phase

** Postponed or terminal cell division

Front 15

Decision to Divide

Back 15

** External Factors**

- Environmental Conditions

- Signaling Molecules

**Internal Factors**

- Cell cycle control molecules

- Checkpoints

Front 16

G1 Phase (1ST Gap)

Back 16

*Cell growth occurs during this phase*

** Signaling molecules can cause cell to accumulate molecular changes during G1 that promote progression through the cell cycle**

** If cell passes the restriction point, or G1 checkpoint, the cell becomes committed to enter S phase and replicate DNA**

Front 17

S Phase (Synthesis of DNA)

Back 17

**Chromosomes replicate**

After replication, 2 copies stay joined to each other and are called Sister Chromatids

**Human cell in G1 has 46 chromosomes

**Same cell in G2 has 46 pairs of Sister chromatids or 92 chromatids total

Front 18

G2 Phase (2nd Gap)

Back 18

Cell synthesizes proteins needed during Mitosis and Cytokinesis

Front 19

M Phase (Mitosis and Cytokinesis)

Back 19

**Mitosis - Division of one cell nucleus into 2 with separation of sister chromatids

**Cytokinesis- Follows Mitosis to divide the cytoplasm into 2 daughter cells

Front 20

Three Checkpoints

Back 20

**Critical Regulatory Points**

1) G1 Checkpoint

2) G2 Checkpoint

3) Metaphase checkpoint

** Checkpoint proteins act as sensors to determine if cell are in proper condition to divide

**Cell cycle is delayed until problems fixed or prevented altogether

**Loss of checkpoints can lead to mutations and cancer

Front 21

G1 Checkpoint

Back 21

Restriction point conditions favorable for cell division

Front 22

G2 Checkpoint

Back 22

Levels of proteins required to continue through M phase

Front 23

Metaphase Checkpoint

Back 23

Integrity of the spindle apparatus

Front 24

Mitotic Cell Division

Back 24

** Cell divides to produce 2 new cells genetically identical to the original

** Mother cell is original, Daughter cells are new

** Involves Mitosis- nuclei plus cytokinesis- cells

** Used for asexual reproduction or for development and growth of multi-cellular organisms

Front 25

Interphase

Back 25

Phase of cell cycle during which the chromosomes are decondensed and found in the nucleus (G1, S, G2)

Front 26

Preparation for Cell Division

Back 26

**DNA replicated then compacted

** Sister Chromatids- 2 identical copies with associated proteins

** Chromatids tightly associated at centromere

** Serves as attachment site for the kinetochore which is later used in sorting chromosomes

Front 27

Mitotic Spindle

Back 27

** Ensures that each daughter cell will obtain the correct # and types of chromosomes

** Responsible for organizing and sorting the chromosomes during Mitosis

** Composed of microtubles- protein fibers and components of the cytoskeleton

Front 28

Centrosomes

Back 28

Aka Microtubule organizing Center (MTOC)

** Duplicates at the beginning of M phase

Each defines a pole

Front 29

Spindle Microtubules

Back 29

Spindle formed from Microtubules

Microtubules formed from Tubulin proteins

Front 30

Three types of Microtubules

Back 30

1) Astral Microtubules- Position spindle in cell

2) Polar Microtubules- Separate 2 poles

3) Kinetochore Microtubules- Attached to kinetochore bound to centromeres

Front 31

Mitosis S

Back 31

**Process of dividing one cell nucleus into 2 nuclei

** Each daughter cell with complement chromosome

- Prophase

- Prometaphase

- Metaphase

- Anaphase

- Telophase

Front 32

Prophase

Back 32

** Chromosomes have already replicated and are joined as pairs of sister chromatids

** Nuclear membrane dissociates into small vesicles

** Chromatids condense into highly compated structures that are visible by light microscopy

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Prometaphase

Back 33

** Nuclear envelope completely fragments

** Mitotic spindle is fully formed during this phase

** Centrosomes move apart and demarcate the 2 poles

** Spindle fibers interact with sister chromatids

** 2 kinetochores on each pair of sister chromatids are attached to kinetochore microtubules from opposite poles

Front 34

Metaphase

Back 34

** Pairs of sister chromatids are aligned along a plane halfway between the poles called the Metaphase Plate

** Organized into a single row

** When alignment is complete, the cell is in metaphase

Front 35

Anaphase

Back 35

** Connections broken between sister chromatids

** Each individual chromatid is linked to only one pole by kinetochore microtubules

** Kinetochore microtubules shorten, pulling chromosomes toward the pole to which they are attached

** The poles move away from each other as overlapping polar microtubules lengthen and push against each other

** Chromatids are equally distributed

Front 36

Telophase

Back 36

** Chromosomes have reached their respective poles and decondense

** Nuclear membranes now re-form to produce 2 separate nuclei

Front 37

Cytokinesis

Back 37

** Mitosis is quickly followed by Cytokinesis in most cases

** 2 nuclei are segregated into separate daughter cells

**Process is different in animals and plants**

- Animals- Cleavage furrow constricts like a drawstring to separate the cells

- Plants- Cell plate forms a cell wall between the two daughter cells

Front 38

Meiosis and Sexual Reproduction

Back 38

** Sexual reproduction requires a fertilization event in which 2 haploid gametes unite to create a diploid cell called a Zygote

** Meiosis is the process by which haploid cells are produced from a cell that was originally diploid - Sperm or egg cell with 23 chromosomes

** 2 rounds of division are necessary

Front 39

Crossing Over

Back 39

** Physical exchange between chromosome pieces of the crossing bivalent

** Increase the genetic variation of a species

** Number of crossovers carefully regulated

Front 40

Chiasma

Back 40

Arms of the chromosomes tend to separate but remain adhered at the crossover site

Front 41

Meiosis I

Back 41

End of meiosis I- 2 haploid cells, with no pairs of homologous chromosomes

Front 42

Prophase I

Back 42

Chromosomes condense, bivalents form and the nuclear membrane breaks down

Front 43

Prometaphase I

Back 43

Spindle apparatus complete, chromatids attach to kinetochore microtubules

- Pairs of sister chromatids attached to Single pole

Front 44

Metaphase I

Back 44

Bivalents organized along metaphase plate as double row

- Mechanism to promote genetic diversity

Front 45

Anaphase I

Back 45

Segregation of homologues occurs

** Connections between bivalents break, but sister chromatids stay connected together

** Each joined pair of chromatids migrates to one pole, while homologous pair moves to the opposite pole

Front 46

Telophase I

Back 46

Sister chromatids have reached their respective poles and decondense and nuclear membranes reform

** Cytokinesis

Front 47

Meiosis II

Back 47

** No S phase between meiosis I and meiosis II

** Sorting events of meiosis II are similar to those of mitosis

** Sister chromatids separated in anaphase II, unlike anaphase I

Front 48

Chromosomal Mutations

Back 48

** Deletions- Segment of chromosome missing

** Duplication- Repeated segment of chromosome

** Inversions- A segment has a change in direction along a single chromosome (Can break genes at ends or separate from regulatory regions)

** Translocations- One segment becomes attached to another chromosome, may be simple or reciprocal

Front 49

Euploid

Back 49

Normal number of chromosomes

** 2 sets is normal in a diploid organism

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Polyploid

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3 or more sets of chromosomes

** Triploid- 3n

** Tetraploid- 4n

Front 51

Aneuploidy

Back 51

Abnormal number of a particular chromosomes

**Trisomic- normal 2 copies of a chromosome plus a 3rd 2n+1, ex: Trisomy 21 Down Syndrome

** Monosomic- Missing one of normal copies of a chromosomes 2n-1

Front 52

Nondisjunction

Back 52

** Chromosomes do not sort properly during cell division

** During meiosis can produce aneuploid gametes