Humans have 23 unique chromosomes the human n number

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Humans have 23 unique chromosomes. The human N number is thus 23. Duplication of this chromosome into chromatids (by DNA replication) Centromere Chromosome 1N Sister Chromatids 1N 1N 1N As cells divide and sister chromatids become disconnected, they are considered distinct chromosomes. Sister chromatids end up in different cells During cell division, the chromatids separate into chromosomes
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Useful Terms When referring to chromosomes, there are two basic kinds of cells: Somatic Cells : These are regular Body Cells (skin, muscle, brain, etc.). Each somatic cell has 2 copies of each type of chromosome. Human somatic cells have 46 chromosomes: They are 2N = 2 x 23 = 46. Gametes: These are sex or reproductive cells, i.e., eggs or sperm cells. Each sex cell contains one copy of each chromosome. In humans, each egg & each sperm has 23 chromosomes, i.e., 1 copy of each type of chromosome. Thus, gametes are 1N. In human eggs and sperm, 1N = 23. Genome: Is a term meaning the total DNA of nucleotide content of a cell or organelle. For example: The nuclear genome The mitochondrial genome The chloroplast genome Mitosis is the process of distributing chromosomes into daughter
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2 of each chromosome 2N 2 chromatids for each chromosome 2N 2N In Mitosis, the division of a 2N somatic cell--i.e., a cell with 2 copies of each kind of chromosome--results in two somatic cells, each with 2N chromosomes. Here is a cell with 2 kinds of chromosomes, red and green. Duplication of Chromosomes (DNA replication) in a single cell Cell Division Daughter Cells
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Cell reproduction video
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The Cell Reproductive Cycle Interphase : The cell gets ready for cell division G1 (Gap 1): The cell produces all the stuff that is needed after division —e.g., extra organelles and cytoplasm S: Chromosome duplication . This is when DNA replication occurs DNA polymerase makes a copy of each DNA molecule. G2 (Gap 2): Here the cell produces the enzymes and structures needed for mitosis and cytokinesis Mitotic phase : This is a short period when chromosomes separate to different ends of the cell in preparation for packaging into the two daughter cells Mitosis has 5 sub-phases Cytokinesis is the actual division of the cell
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During G 2 of Interphase, when the cell is getting ready for mitosis Centrosomes (microtubule organizing centers) duplicate Microtubules extend out from centrosomes as asters (star-like structures) Chromosomes are still relaxed as diffuse chromatin —they do not have the characteristic elongate form yet. DNA already has already been duplicated in the S phase.
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Mitosis & Cytokinesis Overview The 5 subphases of mitosis and then cytokinesis: Prophase (Prometaphase) Metaphase Anaphase Telophase Cytokinesis
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Prophase Nucleoli disappear Chromatin condenses into visible chromosomes Microtubules from centrosome asters elongate to initiate the mitotic spindle
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