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Chapter 8

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Biology 1225
Michael Butler

Chapter 8 - How Cells Replicate 8.5 will not be tested - The fusion of 2 gametes create a single fertilized zygote as the beginning of an organism’s life cycle. - The cell must go through several thousand rounds of cell division to produce the large population of cells needed to construct the body of a multicellular organism - Throughout this process of cell division the genetic material must be replicated, condensed and portioned into daughter cells. This type of cell division is called MITOSIS. - For sexually reproducing organisms, the gametes mentioned above are created in gonads by a specialized type of cell division that must reduce the amount of genetic material by half – This is MEIOSIS. - Our body (Somatic cells) are diploid, our gametes are haploid - Know Fig 8.5 and Fig 8.13 It is essential to understand meiosis and mitosis before working on inheritance - Humans inherit 23 chromosomes from each parent so that we end up with 2 copies of each. Ie. We have 23 pairs of chromosomes. - Whenever a cell needs to divide it replicates all of the chromosomes and then splits them down the middle giving one of each to each of the 2 daughter cells – daughter cells are identical to the mother cell - Cells that need to produce gametes replicate all of the chromosomes and split them, but the split is different this time - Instead of splitting each replicated chromosome – Meiosis begins by splitting the members of each pair into daughter cells - The reduces the number of chromosomes - A second division splits the replicated chromosomes down the middle and results in gametes having only half the number of chromosomes as the original gonad cell 1 8.2 Multiplication by Division pg. 133 Asexual Reproduction - mode by which offspring arise from a single parent only Meiosis – nuclear division process that halves the chromosome number. Basis of sexual reproduction Mitosis – nuclear division mechanism that maintains the chromosome number. Basis of body growth, tissue repair and replacement in multi celled eukaryotes; also asexual reproduction in some plants, animals, fungi and protists. Sexual reproduction – reproductive mode by which offspring arise from two parents and inherit genes from both. 1. A cell reproduces by dividing; nucleus first, then cytoplasm. 2. Each descendant cell receives a complete set of chromosomes and some cytoplasm 3. Nuclear division mechanisms of mitosis and meiosis partition chromosomes of a parent cell into new nuclei. 4. Mitosis is the basis of growth, cell replacement and tissue repair in multi celled species and asexual reproduction in many species. 5. Meiosis is the basis of sexual reproduction in eukaryotes Take Home Message 1. When a cell divides, each descendant cell receives a set of chromosomes and some cytoplasm. In eukaryotic cells, the nucleus divides first , then cytoplasm 2. Mitosis is a nuclear division mechanism that maintains the chromosome number. It is the basis of body size increases, cell replacements, and tissue repair in multi celled eukaryotes; and asexual reproduction in single celled and some multi celled eukaryotes 3. Meiosis, a nuclear division mechanism that halves the chromosome number is the basis of sexual reproduction in eukaryotes 2 8.3 Mitosis and the Cell Cycle pg. 134 cell cycle – A series of events from the time a cell forms until its cytoplasm divides homologous chromosomes paired chromosomes with the same length, shape and set of genes interphase – in eukaryotic cell cycle, the interval between mitotic division when a cell grows, roughly doubles the number it its cytoplasmic components and replicates its DNA anaphase- stage of mitosis during which sister chromatids separate and move towards opposite sides of the cell metaphase– stage of mitosis at which all chromosomes are aligned in the middle of the cell prophase – stage of mitosis during which chromosomes condense and become attached to a newly forming spindle spindle – apparatus that moves chromosomes during nuclear division; consists of dynamically assembled and disassembled microtubules telophase – stage of mitosis during which chromosomes arrive at opposite ends of the cell and de condense, and two new nuclei form. 3 1. A cell cycle includes all the stages through which a eukaryotic cell passes during its lifetime; it starts when a new cell forms, and ends when the cell reproduces. 2. Most of a cell’s activities, including DNA replication of its homologous chromosomes, occur during interphase 3. Mitosis maintains the chromosome number 4. During prophase, the duplicated chromosomes condense. Microtubules form a spindle, and the nuclear envelope breaks up. Spindle microtubules attach to the chromosomes at the centromere. 5. At metaphase, all of the chromosomes are aligned in the middle of the cell. 6. During anaphase, the sister chromatids of each chromosome detach and move toward opposite sides of the cell 7. During telophase, a nuclear envelope forms around the two clusters of chromosomes. Two new nuclei, each with the parental chromosome number are the result. Take Home Message What happens during the cell cycle? 1. A cell’s life passes through a series of stages that include interphase, mitosis, and cytoplasmic div
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