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Meiosis Notes

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Meiosis Revision

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Meiosis Key terms PLOIDY- refers to the number of copies of each chromosome present in the cell nucleus N (number)- refers to the number of copies of each unique double stranded DNA molecule in nucleus
-haploid gametes with one DNA molecule per chromosome are 1N
-diploid cells with one DNA per chromosome (mother and father)- 2N Meiosis- process of cell division that occurs only in the germ line. Diploid germ cell undergoes 2 successive nuclear and cell division to form 4 haploid gametes that are 1N cells Stages
-preliminary step in meiosis is the replication of chromosomal DNA molecule, diploid cell is converted from 2N to 4N. Once the DNA replicates, there are 2 chromatids are joined together at a structure called the centromere This stage forms the primary oocyte and in males the primary spermatocyte Meiosis 1- reduction cell division Prophase
-chromosomes condense into a compact double stranded structure
-late stages of prophase, the double stranded chromosomes of each homologous pair match up, centromere to centromere, to form a joint structure known as a chiasma
-chiasma formation makes is possible for 2 homologous chromosomes to exchange large segments of DNA by a process called crossing over- exchange of maternal and paternal genes
-recombination of genetic material on homologous maternal and paternal chromosomes is random and increases the genetic variability of the future gametes At this stage, the primary oocyte enters a phase of meiotic arrest Metaphase
-four stranded chiasma structures are organised on the equator of spindle apparatus

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