One of each chromosome pair is destined to be carried to one pole, the other to the opposite pole.ĭuring metaphase, each chromosome is aligned and ready to be transported to either pole. If a centromere is damaged, no kinetochore will form and there will be no anaphase. Microtubules have a ‘slow-growing’ (minus) end attached to the PCM of each centrosome, and a ‘fast-growing’ (plus) end which grows towards the metaphase plate.ĭuring prometaphase, kinetochore proteins form close to the centromeres of the chromosomes and attach to the nearest microtubule. It is important that four structures are available, as these will split into two pairs – one pair for each daughter cell.ĭuring prophase, centrosomes separate and migrate to two opposite poles outside of the disintegrating nuclear membrane, where they produce longer microtubules that reach to the cell center (the metaphase plate or equatorial plate). The original and daughter centrioles are attached and will remain so until the prophase stage of mitosis or prophase I of meiosis is initiated. A pair of centriolesĪ centriole pair is not attached, but during the replication stage (synthesis, or S-stage) of the cell cycle, they are also replicated to form daughter centrioles. When combined with pericentriolar material (PCM) they form a centrosome. Centrioles are the main components of the centrosome and appear as short microtubule cylinders in a star-like assembly consisting of groups of three microtubules, as seen in the image below. Four genetically unique daughter cells are produced.Centrosomes have been commonly believed to be the primary manufacturing units of the spindle apparatus. Nuclear envelope reforms and cytokinesis takes places. Telophase II: chromatids reach opposite poles of the cell. Metaphase II: chromosomes attach to the spindle fibre by their centromeres.Īnaphase II: sister chromatids are separated. Prophase II: chromosomes condense, nuclear envelope disintegrates and spindle fibres form. Cytokinesis results in the formation of two daughter cells. Nuclear envelope reforms around the chromosomes. Telophase I: chromosomes reach opposite poles of the cell. Metaphase I: homologous chromosomes line up along the equator and attach to the spindle fibre by their centromeres.Īnaphase I: homologous chromosomes are separated The nuclear envelope disintegrates and spindle fibres form. Prophase I: chromatids condense and arrange themselves into homologous pairs (called bivalents). Interphase: the DNA replicates so there are now two identical copies of each chromosome (referred to as chromatids). Meiosis involves two rounds of cell division which are referred to as meiosis I and meiosis II. When two haploid gametes join during fertilisation, a diploid cell called a zygote is formed. Unlike mitosis, the daughter cells are genetically different from the parent cell and contain just half the number of chromosomes (i.e. Meiosis is the type of cell division which produces gametes for sexual reproduction. The cytoplasm divides ( cytokinesis) and the plasma membrane pinches off to form two new, genetically-identical cells. Telophase & cytokinesis - the two groups of chromsomes decondense (they become long and thin) and a nuclear envelope reforms around them, forming two new nuclei. They attach to the spindle fibre by their centromere.Īnaphase - the centromere splits and the chromatids are pulled to opposite poles of the cell. Metaphase - the chromosomes line up along the middle of the cell. The centrioles move to opposite poles of the cell and form spindle fibres. Prophase - the chromosomes condense (they become shorter and fatter) and the nuclear envelope disintegrates. The mitochondria produce more ATP which will provide the energy for cell division. Once the DNA has replicated, each chromosome now consists of two sister chromatids, connected by a structure called the centromere. Interphase - the cell prepares for mitosis by growing larger, replicating its organelles and synthesising new DNA (see above).
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