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Topic 5 ‐ Crossing over and independent assortment Why aren’t offspring identical to each other if they all get half chromosomes from dad and half from mom? http://highered.mcgraw‐hill.com/sites/dl/free/0072835125/126997/animation5.html (on next page) In meiosis, the new cells have different combinations of genetic material than the parent cell n As opposed to mitosis in which the daughter and parent cell have identical genetic material Meiosis produces genetically different cells through two different processes n Independent assortment n Crossing over Crossing over When homologous chromosomes pair up during prophase I (synapsis), they may exchange pieces of chromosome This is known as crossing over As a result, individual chromosomes contain some genes of maternal origin and some genes of paternal origin. Gene – a specific unit of DNA that expresses a certain trait Allele – different forms of the same gene ‐ Expressed on homologous chromosomes 1 2 Independent assortment http://highered.mcgraw‐hill.com/sites/0072495855/student_view0/chapter3/animation__random_orientation_of_chromosomes_during_meiosis.html During metaphase I, homologous chromosomes align along the equatorial plate In each pair, the chromosome of maternal origin is orientated towards one pole, and the paternal chromosome is orientated toward the other pole. Therefore, some maternal and some paternal chromosomes face the same pole of the cell This results in new cells that have mixtures of the paternal and maternal chromosomes 3