MEIOSIS

• Every Living creature on earth begins in a single Cell.
• The Cell then does mitosis, dividing over and over again with certain cells becoming Specialized.
• Eventually, the Cell becomes a Human.
• Meiosis reduces the amount of genetic information.
• Meiosis produces haploid gametes or spores with only one set of chromosomes.
• Meiosis involves two successive divisions: Meiosis I and Meiosis II.
• In most species, Cytokinesis follows, producing two daughter cells.
• Notable events of Anaphase I include chromosomes in each tetrad separating and migrating toward the opposite poles, with the sister chromatids (dyads) remaining attached at their respective centromere regions.
• Notable events of Telophase I include dyads completing their migration to the poles, and the formation of new nuclear membranes.
• Prophase II, Metaphase II, Anaphase II, and Telophase II are notable events in Meiosis II.
• Microtubules are attached to the centromere regions of the homologues.
• Meiosis II is similar to mitotic division, but differs in the number of chromosomes that each daughter cell receives, which is half the number.
• Each nucleus in Telophase I contains only one set of chromosomes.
• This is because Y chromosome is very small and carries few genes.
• Nondisjunction happens when members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II.
• Within the human body, meiosis occurs repeatedly as the testes or ovaries produce gametes.
• In nondisjunction, one gamete receives two of the same type of chromosome and another gamete receives no copy.
• Accidents during Meiosis can alter Chromosome number.
• The other chromosomes are usually distributed normally in nondisjunction.
• A Karyotype is an ordered display of magnified images of an individual’s chromosome arranged in pairs.
• This is a Karyotype of an organism with nondisjunction in its Chromosome 21.
• In most cases, a human embryo with an abnormal number of chromosomes is spontaneously aborted (miscarried) long before birth.
• Accidents also happen in sex chromosomes.
• Unusual number of sex chromosomes seem to upset the genetic balance less than unusual number of autosomes.
• Reduction divisions are a unique feature of meiosis, where chromosomes do not replicate between the two nuclear divisions, resulting in each cell containing only half the original complement of chromosomes.
• Notable events of Prophase I include the occurrence of chiasmata and spindles connecting at the kinetochore of the homologue during late Prophase.
• Prophase I involves the crossing over and recombination of genetic material between non-sister chromatids, resulting in the genetically unidentical, haploid daughter chromatid cells.
• Genetic exchange occurs between the homologous chromosomes, a process known as homologous recombination.
• Diakinesis is the final stage of meiosis, where transcription ceases and chromosomes recondense.
• Metaphase I is a notable event in meiosis, where tetrads are now at the metaphase plate.
• Meiosis I results in reducing the number of chromosomes, a process known as reduction division.
• Homologous chromosomes find each other if they have the same location of genes, location of centromere, and chromosomal length.
• Notable events of Prophase I include centrosome movement, spindle formation, and nuclear envelope breaks down.
• Synapsis is a process where homologous chromosomes or homologues pair all along their length.
• Leptotene -chromosomes are tightly condensed.
• Zygotene

  homologous chromosomes begin to pair and twist around each other.
• Pachytene begins when synapsis is complete (right after synaptonemal complex forms).
• Diplotene

  protein lattice of synaptonemal complex begins to disassemble.
• 3 Unique features of Meiosis SYNAPSIS, HOMOLOGOUS RECOMBINATION and REDUCTION DIVISION
• 3 Unique features of Meiosis 


  SYNAPSIS, HOMOLOGOUS RECOMBINATION and REDUCTION DIVISION