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Videos de Conceptos Relacionados

Crossing Over01:34

Crossing Over

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where each chromosome—replicated in S phase—is now composed of two sister chromatids (identical copies) joined centrally.
The homologous pairs of sister chromosomes—one from the maternal and one from the paternal genome—then begin to align alongside each other lengthwise, matching corresponding DNA positions in a process called synapsis.
In order to...
Crossing over01:34

Crossing over

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where each chromosome—replicated in S phase—is now composed of two sister chromatids (identical copies) joined centrally.
The homologous pairs of sister chromosomes—one from the maternal and one from the paternal genome—then begin to align alongside each other lengthwise, matching corresponding DNA positions in a process called synapsis.
In order to...
Crossing Over01:30

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to allelic diversity in the newly formed daughter cells. In humans, crossing over produces genetically distinct haploid egg and sperm cells that undergo fertilization to produce unique offspring. Before cell division starts, the germ cell’s chromosome(s) undergo duplication in the S phase of the cell cycle. As the cells enter prophase I, duplicated...
Phase Diagrams of Ternary Systems01:28

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Consider a ternary system, which is composed of three components: water (W), ethanoic acid (E), and trichloromethane (T). Here, Ethanoic acid (E) is fully miscible with both water (W) and trichloromethane (T), meaning it can mix entirely with either of them. However, water and trichloromethane have partial miscibility, meaning they can only mix to a certain extent, beyond which two separate phases will form.The phase diagram of a ternary system is represented as an equilateral triangle, where...
The Chain Rule01:30

The Chain Rule

A system of interconnected gears provides a concrete physical interpretation of the Chain Rule in calculus. Consider three gears arranged in sequence, where the rotational speeds of the first, second, and third gears are represented by the variables x, z, and y, respectively. The first gear drives the second, and the second drives the third, so the motion of each gear depends on the one preceding it. This structure naturally leads to a two-stage variable relationship that can be analyzed using...
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Chronic bronchitis is a key phenotype of chronic obstructive pulmonary disease (COPD), characterized by airway-centered inflammation and mucus overproduction. It develops from long-term exposure to harmful particles or gases, most commonly cigarette smoke, which triggers a persistent inflammatory response.Cellular and Structural ChangesInflammation initially affects the large bronchi and later the smaller airways, with infiltration by immune cells, including neutrophils, macrophages, and...

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Updated: Jun 14, 2026

Getting an A with the 3Cs: Chromosome Conformation Capture for Undergraduates
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La transición entre el Cretácico y Terciario.

C B Officer, C L Drake

    Science (New York, N.Y.)
    |March 25, 1983
    PubMed
    Resumen
    Este resumen es generado por máquina.

    El límite entre el Cretácico y Terciario.

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    Área de la Ciencia:

    • Paleontología Paleontología.
    • Geología Geología Geología.
    • La geoquímica es la geoquímica.

    Sus antecedentes:

    • El límite Cretácico-Terciario (K-T) marca una transición significativa en la historia de la Tierra, caracterizada por grandes cambios en la fauna y una anomalía de iridio.
    • Las interpretaciones anteriores sugirieron un evento de impacto extraterrestre como la causa principal de estos fenómenos del límite K-T.
    • Las variaciones en los registros fósiles y datos geoquímicos presentan complejidades en la comprensión de la transición K-T.

    Objetivo del estudio:

    • Evaluar críticamente la hipótesis de impacto extraterrestre para los cambios faunísticos del límite K-T y la anomalía de iridio.
    • Explorar explicaciones alternativas para los registros geológicos y paleontológicos observados en la transición K-T.
    • Para sintetizar diversos datos, incluidas las evidencias fósiles, la distribución del iridio y la mineralogía de arcilla, para reevaluar el evento del límite K-T.

    Principales métodos:

    • Análisis de secuencias fósiles de muestras de núcleo a través de la frontera K-T.
    • Examen de los patrones de distribución del iridio y la abundancia de metales nobles en varios sitios.
    • Evaluación de la mineralogía arcillosa y los efectos de deposición en las arcillas de la capa límite.

    Principales resultados:

    • Se observaron variaciones significativas en los tiempos e intervalos de transición de los fósiles dependiendo de la ubicación y los indicadores fósiles.
    • Inconsistencias identificadas en la distribución del iridio, cantidades totales y abundancias normalizadas de metales nobles en diferentes sitios.
    • Se resaltaron los posibles efectos de deposición en la reducción de los ambientes y la distinta mineralogía arcillosa en la capa límite.

    Conclusiones:

    • La hipótesis del impacto extraterrestre se cuestiona debido a las variaciones en los datos fósiles y geoquímicos.
    • Los eventos terrestres, como el vulcanismo extenso, la regresión del nivel del mar y los cambios paleoclimáticos, ofrecen explicaciones más plausibles para los cambios en los límites K-T.
    • La investigación continua en diversos fenómenos terrestres es crucial para una comprensión completa de la transición Cretácico-Terciario.