Meiosis Meiosis

Meiosis I y IIMeiosis I y II

2n

Diploide

Meiosis

Una célula madre diploide pasa por dos divisiones celulares dando origen a cuatro células hijas haploides con recombinación genética. Diapositiva 5

Diapositiva 2

Haploides (N)

CRECIMIENTO

EN QUE CELULAS OCURRE LA MEIOSIS

ANIMALES:de la línea germinativa en gónadas masculinas y

femeninas

VEGETALES: células madres: Megasporas y microsporas

HONGOS: células madres de esporas Diapositiva 5

INTERCINESIS (sin duplicación de ADN) MEIOSIS II (ecuacional)Diapositiva 17 PROFASE IIDiapositiva 17 METAFASE II (ubicación en la placa ecuatorial) ANAFASE II (separación de cromátidas y

migración a los polos) TELOFASE II CITOCINESIS (cuatro células hijas haploides y

con Material genético recombinado).Diapositiva 17LAS COMBINACIONES VARIAN SEGÚN LA

DISPOSICIÓN Y SEPARACION DE LOS CROMOSOMAS Diapositiva 17 Diapositiva 19

DescripciónDiapositiva 1 Diapositiva 3

Maternal set ofchromosomes (n = 3)

2n = 6

Paternal set ofchromosomes (n = 3)

Two sister chromatidsof one replicatedchromosomes

Two nonsister chromatids in a homologous pair

Pair of homologouschromosomes(one from each set)

Centromere

Centrosomes(with centriole pairs)

Nuclearenvelope

Chromatin

Chromosomes duplicate

INTERPHASE

METAPHASE I

Prophase Iof meiosis

Tetrad

Nonsisterchromatids

Chiasma,site of crossingover

Recombinantchromosomes

Metaphase I

Metaphase II

Daughtercells

Diapositiva 1

Fuente: www.bio.miami.edu

CIGOTENODiapositiva 3

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

Diapositiva 3

Sisterchromatids

Chiasmata

Spindle

Centromere(with kinetochore)

Metaphaseplate

Homologouschromosomesseparate

Sister chromatidsremain attached

Microtubuleattached tokinetochore

Tetrad

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

Diapositiva 3

Cleavagefurrow

MEIOSIS II: Separates sister chromatids

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I AND

CYTOKINESISTELOPHASE II AND

CYTOKINESIS

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

Diapositiva 4

Key

Maternal set ofchromosomes

Paternal set ofchromosomes

Possibility 1 Possibility 2

Combination 2Combination 1 Combination 3 Combination 4

Daughtercells

Metaphase II

Two equally probablearrangements ofchromosomes at

metaphase I

Diapositiva 4

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 II

Daughter cellsof mitosis

2n2n

n

Sister chromatids separate during anaphase II

n n n

Daughter cells of meiosis II

GAMETOGENESIS Diapositiva 21 Diapositiva 22

Fuente: www.bio.miami.edu

Diapositiva 22

Fuente: academic.pgcc.edu

IMPORTANCIA BIOLOGICA DE LA MEIOSIS

Intercambio de material genético Recombinación genética Variabilidad genética Materia prima para la evolución

Diapositiva 25

Errores meiErrores meióóticosticos

A.- A.- Homólogos sin desunir no se separan en meiosis 1 

1.Resultados en aneuploide 

2.Usualmente letal para el embrión

3.Trisomía 21, excepción que conduce al síndrome de Down.

B.- Cromosomas sexuales

1.Síndrome de Turner: monosomia X 

2.Síndrome de Klinefelter: XXY