MEIOSIS - Cell Division
• Multicellular organisms such as ourselves have _______________ of cells: ________________ cells ____________________ cells (all general ___________ cells) (sex cells -­‐-­‐-­‐ _____________) # of chromosomes: ____________ ____________ (in humans) ______ = 46 ______ = 23 contain pairs of contain only one set of homologous chromosomes chromosomes • Each type of organism has a characteristic __________________ in its somatic cells. • Mitosis _________ occurs in ____________ cells, ________ reproductive cells. • Meiosis occurs in the ___________________________ (testes and ovaries) and produces _____________ -­‐ (___________ and ________ cells). • Meiosis has 2 purposes: 1) ___________________ -­‐ reduces the number of ________________ to one half of the normal number (_____________________) 2) ____________________ -­‐ ____________ produced by _____________ have different combinations of ____________ (gene variations). This increases ___________________ in a population. The Haploid-Diploid Cycle of Sexual Reproduction in Humans • The process of Meiosis involves ________ division: 1) the _________ divisions is a called _________________ -­‐ _______________________ and ____________________________________ occur -­‐ ____________________________ separate and one member from each pairing goes into each new cell ( ____ cells) 2) the _____________divisions is a called _________________ -­‐ _____________________________ from each double-­‐stranded chromosome separate -­‐ each new cell ( ____ cells) contains only one complete set of unpaired chromosomes -­‐ this division is ____________________ to mitosis. • Meiosis is the process by which ______________ are formed. How is Genetic Variability created during Meiosis?? 1) Crossing Over • During ___________________, _________________ chromosomes pair up (____________) • _____________ chromatids may exchange bits of DNA with ______________ chromatids • A section of chromosome that is ________________ may contain hundreds or even thousands of ___________ • As a result, individual chromosomes may contain bits of both ___________ and __________ DNA Crossing Over 2) Random (________________) Assortment • Maternal and paternal chromosomes line up randomly along the equator in __________ • This _________________ allows different ___________________ of chromosomes to be found in the _________________ • 2n possibilities = _______ = _________________ possible gametes Random Assortment