Set_4A_Dr._Wilson_MCDB1A.2010

Set_4A_Dr._Wilson_MCDB1A.2010 - Set 4A Meiosis Occurs in...

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Meiosis Occurs in all organisms that have a sexual life cycle Set 4A
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Cells of organisms that have a sexual life cycle have cells that have two complete sets of chromosomes, one from each parent. Such cells are called diploid ( 2n ). They will also have cells that have only one complete set of chromosomes. Such cells are called haploid ( 1n or simply n ).
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In human diploid cells one member of each pair was donated by one parent, the second was donated by other parent The pairs are called homologous chromosomes ( homologs ) Human cells have 23 pairs of chromosomes ( 46 chromosomes in total ) - 22 of the pairs are homologous pairs, (the 23rd pair is not- these are the sex chromosomes) The two chromosomes of a homologous pair contain the same genes (but they are not identical)
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During formation of eggs and sperm where meiosis occurs, one homolog is retained and the other is lost. So, mature eggs and sperm are haploid (or 1 n) The diploid state (2n) is regained when an egg cell is fertilized by a sperm cell to form a zygote or fertilized egg . Gene re-assortment occurs during meiosis as egg cells and sperm cells are formed and when egg cells and sperm cells combine to form the new individual
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Sexual Reproduction- there are many different versions All sexual life cycles involve meiosis to produce
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Set_4A_Dr._Wilson_MCDB1A.2010 - Set 4A Meiosis Occurs in...

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