Desarrollo y patrones arquitectnicos Presentacin 2 Dr Robert

Desarrollo y patrones arquitectónicos Presentación 2 Dr. Robert J. Mayer ���UPR en Aguadilla http: //math. uprag. edu/rmayer/zoopres 2. ppt

Tareas Leer hasta la página del libro de Carl Safina Escribir una biografía corta del autor y entregarla el 1. 24. 11 Leer los capítulos 8 y 9 del libro de texto “Zoology” Objetivos Conocer los conceptos básicos de la biología del desarrollo Conocer los conceptos básicos de la embriología

Phases of the Cell Cycle • The cell cycle consists of – The mitotic phase – Interphase INTERPHASE S (DNA synthesis) C M yto ito ki si ne s si s G 1 MI (M TOT ) P IC HA SE Figure 12. 5 G 2

• Mitosis consists of five distinct phases – Prophase – Prometaphase G 2 OF INTERPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Figure 12. 6 Nucleolus Nuclear Plasma envelope membrane PROPHASE Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids PROMETAPHASE Fragments Kinetochore of nuclear envelope Nonkinetochore microtubules Kinetochore microtubule

G 2 of Interphase • A nuclear envelope bounds the nucleus. • The nucleus contains one or more nucleoli (singular, nucleolus). • Two centrosomes have formed by replication of a single centrosome. • In animal cells, each centrosome features two centrioles. • Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed. The light micrographs show dividing lung cells from a newt, which has 22 chromosomes in its somatic cells (chromosomes appear blue, microtubules green, intermediate filaments red). For simplicity, the drawings show only four chromosomes.

e PROPHASE Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Prophase • The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope. • The nucleoli disappear. PROMETAPHASE • Each duplicated chromosome appears as two identical sister Fragments Kinetochore chromatids joined together. of nuclear • The mitotic spindle begins to form. envelope Nonkinetochore It is composed of the centrosomes microtubules and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters (“stars”). • The centrosomes move away from each other, apparently propelled by the lengthening microtubules between them. Kinetochore microtubule

ere PROMETAPHASE Fragments of nuclear envelope Kinetochore Nonkinetochore microtubules Kinetochore microtubule Prometaphase • The nuclear envelope fragments. • The microtubules of the spindle can now invade the nuclear area and interact with the chromosomes, which have become even more condensed. • Microtubules extend from each centrosome toward the middle of the cell. • Each of the two chromatids of a chromosome now has a kinetochore, a specialized protein structure located at the centromere. • Some of the microtubules attach to the kinetochores, becoming “kinetochore microtubules. ” These kinetochore microtubules jerk the chromosomes back and forth. • Nonkinetochore microtubules interact with those from the opposite pole of the spindle.

Metaphase • Metaphase is the longest stage of mitosis, lasting about 20 minutes. • The centrosomes are now at opposite ends of the cell. • The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindle’s two poles. The chromosomes’ centromeres lie on the metaphase plate. • For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles. • The entire apparatus of microtubules is called the spindle because of its shape. METAPHASE Metaphase plate Spindle Centrosome at D one spindle pole c

Anaphase • Anaphase is the shortest stage of mitosis, lasting only a few minutes. • Anaphase begins when the two sister chromatids of each pair suddenly part. Each chromatid thus becomes a full. METAPHASE fledged chromosome. • The two liberated chromosomes begin Metaphase moving toward opposite ends of the cell, plate as their kinetochore microtubules shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1 µm/min). • The cell elongates as the nonkinetochore microtubules lengthen. • By the end of anaphase, the two ends of the cell have equivalent—and complete—collections of chromosomes. Spindle ANAPHASE Centrosome at Daughter one spindle pole chromosomes Cl fur Nuc env form

TELOPHASE AND CYTOKINESIS Cleavage furrow Nuclear envelope forming Nucleolus forming Telophase • Two daughter nuclei begin to form in the cell. • Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system. • The chromosomes become less condensed. • Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete. Cytokinesis • The division of the cytoplasm is usually well underway by late telophase, so the two daughter cells appear shortly after the end of mitosis. • In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.

– Metaphase – Anaphase – Telophase METAPHASE ANAPHASE Metaphase plate Figure 12. 6 Spindle Centrosome at Daughter one spindle pole chromosomes TELOPHASE AND CYTOKINESIS Cleavage furrow Nuclear envelope forming Nucleolus forming

• Interphase and meiosis I MEIOSIS I: Separates homologous chromosomes INTERPHASE PROPHASE I Centrosomes (with centriole pairs) Sister chromatids Nuclear envelope METAPHASE I Chiasmata ANAPHASE I Sister chromatids remain attached Centromere (with kinetochore) Spindle Metaphase plate Homologous Microtubule chromosomes Tetrad attached to Chromatin separate kinetochore Pairs of homologous Chromosomes duplicate Tertads line up chromosomes split up Homologous chromosomes (red and blue) pair and exchange Figure 13. 8 segments; 2 n = 6 in this example

• Telophase I, cytokinesis, and meiosis II MEIOSIS II: Separates sister chromatids TELOPHASE I AND CYTOKINESIS PROPHASE II Cleavage furrow Figure 13. 8 Two haploid cells form; chromosomes are still double METAPHASE II ANAPHASE II Sister chromatids separate TELOPHASE II AND CYTOKINESIS Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

Preformación (siglos 17 y 18) Coherencia conceptual 1759 Kaspar Friedrich Wolff – epigénesis

Desarrollo – describe cambios progresivos en un individuo desde su concepción hasta la madurez. . Organismos multicelulares sexuales Rearreglos extensos e interacciones = plan corporal (body plan) y celulas especializadas. Las células especializadas surgen gracias a una serie de condicines creadas en etapas anteriores. En cada paso del desarrollo surgen nuevas estructuras como resultado de interacciones. Cada interacción es incrementalmente restrictiva.

Determinación – localización citoplásmica - inducción

Durante la ovogénesis el óvulo (huevo) se prepara la fertilización y para el comienzo del desarrollo. El espermatozoide es una célula vacía llena de material genético a diferencia del huevo El huevo se prepara durante la profase de meiosis I – producción de cuerpos polares (exceso de citoplasma)

Fertilización externa Fertilización interna Especificidad (quimiotaxis) Se evita la polispermia a. “fast block” cambio en el potencial de la membrana b. “cortical reaction”

Fertilización Restauración del número diploide Activación del óvulo (a veces es lo único) Partenogénesis

Eventos que ocurren durante la fecundación y el desarrollo temprano.

Segmentación (cleavage) en distintos organismos “Cleavage furrow” Isolecitos < Mesolecitos < Telolecitos < Centrolecitos Holoblástico - (tunicados, equinodermos, tunicados, cefalocordados, nemerteos, y la mayor parte de los moluscos, marsupiales y mamíferos placentales) Meroblástico – aves, reptiles, peces, anfibios, moluscos cefalópodos, y mamíferos Monotremos Insectos = Centrolecitos

La cantidad de vitelo determina el tipo de desarrollo temprano del organismo Directo Indirecto

Formación de capas embrionarias (Gastrulación) archenteron Blastulación Blastocelo Blástula (Celoblástula – hueca y Stereoblástula – sólida) = 200 – varios miles de células Se forma en todos los organismos multicelulares El desarrollo continua mas allá de la blástula y se forman capas embrionarias (excepto en las esponjas) Invaginación = gastrulación

Tres capas embrionarias Endodermo Mesodermo Ectodermo Diploblástico Triploblástico Dos cavidades (celoma y sistema digestivo) Celoma – cavidad corporal completamente revestida por mesodermo

Dos tipos de organismos tripoblásticos Los mamíferos son deuterostomados pero su celoma se forma mediante un proceso esquizocélico modificado

Figure 08. 14

Protostomes Deuterostomes