CELL DIVISION MITOSIS: Reproducing the nucleus of a somatic cell. MEIOSIS: Producing sex cells (gametes). CYTOKINESIS: Division of cytoplasm and organelles.

Both mitosis and meiosis consist of a sequence of phases: MITOSIS & MEIOSIS, con’t. Both mitosis and meiosis consist of a sequence of phases: interphase (preparation for division) prophase metaphase anaphase telophase

Result of Mitosis: formation of two daughter nuclei MITOSIS & MEIOSIS, con’t. Result of Mitosis: formation of two daughter nuclei have the same chromosome number as original (parent) cell

Result of Meiosis: Concludes with cytokinesis MITOSIS & MEIOSIS, con’t. Result of Meiosis: formation of 1 to 4 daughter nuclei have half the chromosome number as original (parent) cell Concludes with cytokinesis division of the cytoplasm and organelles

A. Terminology 1. Chromatin 2. Chromosome I. MITOSIS A. Terminology 1. Chromatin 2. Chromosome 3. Diploid (46 or “2N” in humans) 4. Haploid (23 or “N” in humans) 5. Homologous chromosomes 6. Somatic cells

MITOSIS, con’t. B. PHASES: arbitrarily assigned 1. INTERPHASE: a. NO division. Cell appears to be “resting” b. the metabolic phase of the cell

d. Nucleus, nuclear membrane, nucleolus visible Interphase, continued … c. Chromatin visible d. Nucleus, nuclear membrane, nucleolus visible e. Centrioles located at poles f. Longest phase 1. ~96% of the cell’s life cycle 2. average of 23/24 hours

Interphase of Mitosis 1. Interphase (25)

a. Centrioles move to opposite poles of cell MITOSIS, con’t. 2. Prophase a. Centrioles move to opposite poles of cell b. Chromatin condenses into chromosomes c. Nucleoli disappear d. Spindle apparatus is organized

Late Prophase of Mitosis

f. Phase ends as spindle fibers attach to centromeres MITOSIS, con’t.: Prophase e. Toward end of phase, nuclear membrane dissipates f. Phase ends as spindle fibers attach to centromeres g. Each chromosome now consists of two chromatids

Chromosome at Metaphase A single metaphase chromosome with two chromatids 11. Micrograph of Chromosome

a. Chromosomes arranged around equatorial plate MITOSIS, con’t. 3. Metaphase a. Chromosomes arranged around equatorial plate b. “Single file” c. Two spindle fibers attached at each centromere

d. A relatively short phase e. Chromosomes easily counted (KARYOTYPE) MITOSIS, con’t.: Metaphase d. A relatively short phase e. Chromosomes easily counted (KARYOTYPE) f. Phase ends as chromatids separate g. Centromere splits as DNA replication is completed

Metaphase of Mitosis 4. Metaphase (28)

a. Begins as chromatids separate MITOSIS, con’t. 4. ANAPHASE a. Begins as chromatids separate b. Spindles move chromosomes to opposite poles c. Polar spindles elongate cells d. Phase ends when chromosomes have arrived at poles

Anaphase of Mitosis 6. Late Anaphase (30)

a. “Reverse” of prophase MITOSIS, con’t. 5. Telophase a. “Reverse” of prophase b. Identical sister chromosomes have arrived at opposite poles c. Nuclear membrane reassembles d. Spindle apparatus dissipates e. Nucleolus reassembles

f. Chromosomes relax  chromatin MITOSIS, con’t.: Telophase f. Chromosomes relax  chromatin g. Centrioles replicate h. Each chromosome consists of a single complete strand of DNA i. Phase ends when nuclear membrane is completely reassembled

9. Interphase (33) Telophase of Mitosis

1. Begins during anaphase MITOSIS, con’t. … C. CYTOKINESIS 1. Begins during anaphase 2. Completed during telophase 3. Result: two daughter cells a. Genetically identical to parent cell b. Contain ~1/2 the cytoplasm, organelles

An overview of Mitosis showing all stages 10. Mitosis, Nuclear Division (34)

II. MEIOSIS: A special case of mitosis Occurs during maturation of sex cells (gametes) Result: daughter nuclei receive one half the number of chromosomes of somatic cells Makes sexual reproduction possible

II. MEIOSIS, con’t. A. Terminology 1. Haploid: having a single set of chromosomes per individual or cell (N) 2. Diploid: having two full sets of chromosomes per individual or cell (2N)

a. Usually find sexual reproduction in diploid organisms II. MEIOSIS, con’t.: Diploid a. Usually find sexual reproduction in diploid organisms b. Provides enormous adaptive advantages: 1. allows for population variations 2. Increases chances for survival

3. Homologous chromosomes: a. Chromosomes that pair during meiosis II. MEIOSIS, con’t.: Terminology 3. Homologous chromosomes: a. Chromosomes that pair during meiosis b. Have the same morphology c. Contain genes governing the same characteristics

4. Allele: one of the two or more alternate forms of a gene MEIOSIS, con’t.: Terminology 4. Allele: one of the two or more alternate forms of a gene a. dominant, recessive, co-dominant b. examples: B = Brown hair (dominant) b = blonde hair (recessive) c. Different alleles arise by mutations

a. sequence of DNA nucleotides MEIOSIS, con’t.: Terminology 5. Gene: a. sequence of DNA nucleotides b. unit of heredity transmitted in the chromosome 6. Chromosome: sequence of genes

II. MEIOSIS, con’t.: Terminology 7. One gene – One enzyme theory: A gene is that part of a DNA molecule responsible for the synthesis of one enzyme (polypeptide)

B. Phases of Meiosis 1. Two “sets” of events 2. Same names as mitosis II. MEIOSIS, con’t.: B. Phases of Meiosis 1. Two “sets” of events 2. Same names as mitosis 3. Must indicate phase ‘I’ or ‘II’ I = Reductional Division II = Equational Division

C. Reductional Division 1. Interphase I: Like mitosis II. MEIOSIS, con’t.: C. Reductional Division 1. Interphase I: Like mitosis 2. Prophase I: a. Long, complex b. Three subdivisions

II. MEIOSIS, con’t.: Prophase I 1. Early: like mitosis 2. Middle: important a. homologs pair b. crossing over occurs c. exchange of genetic info d. called “tetrads” 3. Late: like mitosis

Prophase I of Meiosis 2. Meiosis I – Middle Prophase I - (38)

b. Homologous pairs align c. One spindle fiber/centromere II. MEIOSIS, con’t.: 3. Metaphase I a. Similar to mitosis b. Homologous pairs align c. One spindle fiber/centromere d. Ends as one of each pair is pulled to opposite poles e. NO DNA replication!!

b. Members of homologous pairs move to poles II. MEIOSIS, con’t.: 4. Anaphase I a. Similar to mitosis b. Members of homologous pairs move to poles c. Moved by spindle fibers

Anaphase II of Meiosis 3. Meiosis I – Early Anaphase I - (39)

a. Nuclear membrane reorganizes b. Chromosomes “relax” II. MEIOSIS, con’t.: 5. Telophase I a. Nuclear membrane reorganizes b. Chromosomes “relax” 6. Cytokinesis: may not occur

Telophase I of Meiosis 5. Meiosis I – Telophase I - (41)

a. Nuclei are haploid (N) b. Chromosome number is reduced by one-half II. MEIOSIS, con’t.: 7. End result a. Nuclei are haploid (N) b. Chromosome number is reduced by one-half

D. Equational Division: 1. Interphase II a. NO DNA replication!! II. MEIOSIS, con’t.: D. Equational Division: 1. Interphase II a. NO DNA replication!! b. “Coffee break” for nuclei c. May not occur

Interphase II of Meiosis 6. Meiosis II – Interphase II - (42) Interphase II of Meiosis

a. Chromosomes condense b. Spindle apparatus forms II. MEIOSIS, con’t.: 2. Prophase II a. Chromosomes condense b. Spindle apparatus forms c. Two fibers/centromere d. Membrane dissipates e. Like mitosis

b. Chromosomes on equator c. Single file II. MEIOSIS, con’t.: 3. Metaphase II a. Like mitosis b. Chromosomes on equator c. Single file d. Ends with centromere replication

Metaphase II of Meiosis 8. Meiosis II – Metaphase II - (44) Metaphase II of Meiosis

a. Centromeres replicate b. Chromatids pulled to opposite poles II. MEIOSIS, con’t.: 4. Anaphase II a. Centromeres replicate b. Chromatids pulled to opposite poles

9. Meiosis II – Late Anaphase II - (45) Anaphase II of Meiosis

b. Nucleolus reorganizes c. Chromosomes relax d. Centrioles replicate II. MEIOSIS, con’t.: 5. Telophase II a. Nuclear membranes reorganize b. Nucleolus reorganizes c. Chromosomes relax d. Centrioles replicate e. Like mitosis

Telophase II of Meiosis 10. Meiosis II – Telophase II – (46) Telophase II of Meiosis

a. Females: unequal division of cytoplasm -one ovum, 3 polar bodies II. MEIOSIS, con’t.: 5. Cytokinesis occurs 6. Result: a. Females: unequal division of cytoplasm -one ovum, 3 polar bodies b. Males: equal division of cytoplasm -four spermatozoa

Telophase II of Meiosis: Four new cells 11. Meiosis II – Sperm Cell – (47) Telophase II of Meiosis: Four new cells

a. Different from parent cell b. Different from each other c. Haploid II. MEIOSIS, con’t.: 7. Cells produced are: a. Different from parent cell b. Different from each other c. Haploid

Spermatogenesis Spermatogenesis results in four spermatozoa

Oogenesis Oogenesis results in one Ovum and two or three polar bodies