MITOSIS Y MEIOSISMITOSIS Y MEIOSIS

OBJETIVOOBJETIVO

• Identificar las fases del ciclo celular.• Identificar las fases de la mitosis.• Explicar la importancia de la mitosis.• Identificar las fases de la meiosis.• Explicar la importancia de la meiosis.

CICLO CELULARCICLO CELULAR

• ¿EN QUÉ CONSISTE?

• ¿QUIÉNES LOS LLEVAN A CABO?

LE 12-5LE 12-5

G1

G2

S(DNA synthesis)

INTERPHASE

Cytokinesis

MITOTIC(M) PHASE

Mitosis

MITOSISMITOSIS

• División del núcleo celular, que da origen a dos núcleos hijos, cada uno con el mismo número de cromosomas que el núcleo progenitor.

• Consta de profase, (prometafase), metafase, anafase, telofase.

IMPORTANCIAIMPORTANCIA

• REPRODUCCIÓN

• CRECIMIENTO Y DESARROLLO

• REPARACIÓN DE TEJIDOS

LE 12-2aLE 12-2a

Reproduction

100 µm

LE 12-2bLE 12-2b

Growth and development

200 µm

LE 12-2cLE 12-2c

Tissue renewal

20 µm

Figure 12-01Figure 12-01

LE 12-4LE 12-4

Chromosomeduplication(including DNAsynthesis)

0.5 µm

Centromere

Sisterchromatids

Separationof sister

chromatids

Centromeres Sister chromatids

LE 12-6aaLE 12-6aa

Centrosomes(with centriole pairs

Chromatin(duplicated)

Early mitoticspindle

Nucleus Nuclearenvelope

Plasmamembrane

Aster

Centromere

Chromosome, consistingof two sister chromatids

Fragmentsof nuclearenvelope

Kinetochore

Nonkinetochoremicrotubules

Kinetochoremicrotubule

LE 12-6baLE 12-6ba

Centrosome atone spindle pole

Metaphaseplate

Spindle

Cleavagefurrow

Daughterchromosomes

Nucleolusforming

Nuclearenvelopeforming

LE 12-9aLE 12-9a

Cleavage furrow100 µm

Contractile ring ofmicrofilaments

Daughter cells

Cleavage of an animal cell (SEM)

LE 12-9bLE 12-9b

1 µm

Daughter cellsCell plate formation in a plant cell (TEM)

New cell wallCell plate

Wall ofparent cell

Vesiclesformingcell plate

MEIOSISMEIOSIS

• Proceso en el que una célula 2n experimenta dos divisiones nucleares sucesivas (meiosis I y meiosis II), con la posibilidad de producir cuatro núcleos n. Conduce a la formación de gametos en animales y esporas en plantas.

IMPORTANCIAIMPORTANCIA

• REDUCCION DEL NÚMERO DE CROMOSOMAS A LA MITAD

• RECOMBINACIÓN GENÉTICAVARIABILIDAD

• FORMACIÓN DE GAMETOS EN LA REPRODUCCIÓN SEXUAL

LE 13-3LE 13-3

5 µmPair of homologouschromosomes

Sisterchromatids

Centromere

LE 13-5LE 13-5Key

Haploid (n)Diploid (2n)

Haploid gametes (n = 23)

Ovum (n)

Spermcell (n)

TestisOvary

Mitosis anddevelopment

Multicellular diploidadults (2n = 46)

FERTILIZATIONMEIOSIS

Diploidzygote(2n = 46)

LE 13-7LE 13-7

Homologous pairof chromosomesin diploid parent cell

Interphase

Homologous pair of replicated chromosomes

Chromosomesreplicate

Meiosis I

Diploid cell withreplicatedchromosomes

Sisterchromatids

Meiosis II

Homologouschromosomesseparate

Sister chromatidsseparate

Haploid cells withreplicated chromosomes

Haploid cells with unreplicated chromosomes

LE 13-8aLE 13-8a

Centrosomes(with centriole pairs)

Sisterchromatids

Chiasmata

Spindle

Centromere(with kinetochore)

Metaphaseplate

Homologouschromosomesseparate

Sister chromatidsremain attached

Microtubuleattached tokinetochore

Tetrad

Nuclearenvelope

Chromatin

Chromosomes duplicate

INTERPHASE MEIOSIS I: Separates homologous chromosomes

PROPHASE I METAPHASE I ANAPHASE I

Homologous chromosomes (red and blue) pair andexchange segments; 2n = 6in this example

Pairs of homologouschromosomes split up

Tetrads line up

LE 13-8bLE 13-8b

Cleavagefurrow

MEIOSIS II: Separates sister chromatids

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I ANDCYTOKINESIS

TELOPHASE II ANDCYTOKINESIS

Sister chromatidsseparate

Haploid daughter cellsforming

Two haploid cellsform; chromosomesare still double

During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes

LE 13-9LE 13-9

Propase

Duplicated chromosome(two sister chromatids)

Chromosomereplication

2n = 6

Parent cell(before chromosome replication)

Chromosomereplication

MITOSIS MEIOSIS

Chiasma (site ofcrossing over) MEIOSIS I

Prophase I

Tetrad formed bysynapsis of homologouschromosomes

Tetradspositioned at themetaphase plate

Metaphase IChromosomes positioned at themetaphase plate

Metaphase

AnaphaseTelophase

Homologuesseparateduringanaphase I;sisterchromatidsremain together

Sister chromatidsseparate duringanaphase

Daughtercells of

meiosis I

Haploidn = 3

Anaphase ITelophase I

MEIOSIS IIDaughter cells

of mitosis

2n2n

n

Sister chromatids separate during anaphase II

n n nDaughter cells of meiosis II

LE 13-11LE 13-11Prophase Iof meiosis

Tetrad

Nonsisterchromatids

Chiasma,site of crossingover

Recombinantchromosomes

Metaphase I

Metaphase II

Daughtercells