Chapter 8 - Chapter 8 The Cellular Basis of Reproduction...

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Chapter 8: The Cellular Basis of Reproduction and InheritanceReproduction:Asexual reproduction- creation of genetically identical offspring by a single parent, without participation of a sperm or egg (ie. Amoeba) “like begets like”Sexual reproduction- offspring resemble both parents but are not identical to parents, each offspring inherits a unique combination of genes form its two parentsChromosomes- structure that contains most of the organisms’ DNAGenome- complete set of inheritable material, chromosomes, genes are inside chromosomes (DNA)Cell Division:Reproduction of cellsRudolf Virchow- “Where a cell exists, there must have been a preexisting cell.”In unicellular organisms, cell division can reproduce an entire organismBinary Fission:“dividing in half”means of asexual reproduction in which a parent organism, often a single cell, divides into two individuals of about equal sizeprokaryotes reproduce by binary fission1.as chromosome duplicates, one copy moves toward the opposite end of cell2.cell elongates3.plasma membrane grows inward, dividing the parent cell into two daughter cellsEukaryotic Cell:More complex and generally much larger than prokaryotic cells, and have many more genes (carry about 25,000 genes versus 3,000 for eukaryote)Chromatin- diffuse mass of long thin fibers of chromosomes, combination of DNA and protein moleculesAs cell prepares to divide, chromatin coils up forming compact, distinct chromosomesThe number of chromosomes depend on the species (Humans-46 chromosomes)Well before the eukaryotic cell begins to divide it duplicates all of its chromosomesSister chromatids- each chromosome consists of two copies, contain identical copies of DNACentromere- two chromatids are joined together by tightly narrow waistCell Cycle:Cell cycle- ordered sequence of events that extends from the time a cell is first formed from a dividing parent until its own division into two cellsConsists of two broad stages- growing stage (interphase-where cell doubles in size and replicates DNA) and cell division (mitotic phase)Interphase-period in eukaryotic cell when the cell is not actually dividingMost of cell cycle is spent in interphase
Cell’s metabolic activity is very high and cell performs its various functions within organismIncreases supply of proteins, creates more cytoplasmic organelles (ribosomes, mitochondria) and grows in sizeThree sub stages- G1, S, G2G1-(first gap)cell growsS- chromosomes are duplicated only during S phase (synthesis of DNA)G2- cell grows, completes preparations for cell divisionMitotic phase (M phase)- part of cell cycle where cell actually divides, accounts for only 10% of cycle, divided into two stages-mitosis and cytokinesisMitosis-nucleus and its contents divide and are evenly distributedCytokinesis- cytoplasm divides into twoProduce two genetically identical daughter cells each with a single nucleus, surrounding cytoplasm, and plasma membraneMitosis:Results in two daughter cells

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