![]() This results in an extra chromosome (n + 1) in two of the gametes and a missing chromosome (n - 1) in two of the gametes. ![]() If nondisjunction occurs in meiosis I, the homologous pair of chromosomes remain bound. Nondisjunction may occur during meiosis I or meiosis II. Four genetically unique daughter cells are produced.\): Nondisjunction in Meiosis: Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, resulting in an abnormal chromosome number. The goal of meiosis is to produce sperm or eggs. You want all your new cells to have the same DNA as the previous cells. The goal of mitosis is to produce two daughter cells that are genetically identical to the parent cell. The goal of mitosis is to produce daughter cells that are genetically identical to their mothers, with not a single chromosome more or less. Nuclear envelope reforms and cytokinesis takes places. The primary difference between these divisions is the differing goals of each process. 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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