This is an extract of our Meiosis document, which we sell as part of our Organisation of the Body Notes collection written by the top tier of Oxford students.
The following is a more accessble plain text extract of the PDF sample above, taken from our Organisation of the Body Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:
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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