Meiosis 1

• Meiosis is a sister type of cell division to mitosis, with both processes producing cells, but in meiosis, four non-identical haploid cells are produced at the end of meiosis II
• In mitosis, one stage produces two identical diploid cells, each with a full set of chromosomes, while meiosis happens in two phases: meiosis I and meiosis II, resulting in four non-identical haploid cells
• During meiosis, a cell with 46 chromosomes can end up with 23 chromosomes in each of the four cells produced, each chromosome being slightly different from the original set
• Interphase is the phase where the cell spends the majority of its time, crucial for DNA replication and ensuring the correct chromosome number for the end of meiosis
• In prophase I of meiosis, homologous chromosomes cross over to create genetic variation, forming bivalents where they exchange genetic information at chiasmata
• Synapsis in prophase I is the movement of homologous partners towards each other to form bivalents, essential for crossing over and creating genetic variation
• Bivalents are formed in prophase I when homologous chromosomes touch each other during crossing over, exchanging genetic information to create recombinant chromatids
• Metaphase I in meiosis is characterized by the alignment of bivalents along the metaphase plate, ready for separation in anaphase I
• Understanding the process of crossing over in prophase I is crucial as it creates genetic variation, increasing the likelihood of survival for organisms
• In metaphase one of meiosis, chromosomes line up on the equator of the cell in a random arrangement, which increases genetic variation
• Metaphase one is identified by chromosomes aligning at the equator, the presence of bi-valence, and double-stranded chromosomes still being present
• Anaphase one is when homologous partners are separated, reducing the chromosome number by half
• Anaphase one is identified by double-stranded chromosomes being pulled to opposite poles and the visibility of recombinant chromosomes
• Telophase one in meiosis is where two separate cells are formed through cytokinesis, resulting in non-identical cells with half the genetic information
• Telophase one is identified by cell cleavage, reforming of the nuclear membrane, and the disappearance of fibers
• Terminology recap for meiosis one:

  • Synapsis: movement of homologous pairs together
  • By-valence: when homologous pairs are touching
  • Diploid: full set of chromosomes
  • Haploid: half the number of chromosomes
  • Crossing over: exchange of genetic information between homologous pairs
  • Random arrangement: chromosomes randomly align at the equator
  • Recombinant chromosomes: chromosomes with exchanged genetic information
  • Homologous pair: set of chromosomes with similar genetic information
  • Chiasmata: point where a bivalence touches
  • Cytokinesis: separation of cytoplasm at the end of telophase
• Meiosis is a sister type of cell division to mitosis, with both processes producing cells, but meiosis results in four non-identical haploid cells carrying half the genetic information of the original cell
• Mitosis produces two identical diploid cells with a full set of chromosomes, while meiosis occurs in two phases - meiosis I and meiosis II, each responsible for different functions
• In meiosis, the cell spends most of its time in interphase, where DNA replication occurs to ensure the correct chromosome number for the transformation from a diploid to a haploid cell
• Interphase is identified by the chromatin network, absence of homologous pairs, and a visible nuclear membrane, crucial for DNA replication and maintaining the correct chromosome number
• Prophase I in meiosis involves crossing over of homologous chromosomes to create genetic variation, identified by condensed chromosomes, disappearing nuclear membrane, and the formation of spindle fibers
• During crossing over in prophase I, homologous chromosomes touch at chiasmata, exchange genetic information, and form bivalents, leading to recombinant chromatids and increased genetic variation
• Metaphase I in meiosis is characterized by bivalents aligning at the metaphase plate, preparing for the separation of homologous chromosomes in anaphase I
• In metaphase one of meiosis, chromosomes line up at the equator of the cell in a random arrangement, which increases genetic variation
• Metaphase one is identified by chromosomes aligning at the equator, the presence of bi-valence, and double-stranded chromosomes still being present
• Anaphase one follows metaphase one and is identified by the separation of homologous partners, halving the chromosome number, and independent assortment for genetic variation
• In telophase one of meiosis, the cytoplasm separates via cytokinesis, forming two non-identical cells with half the genetic information, identified by cell cleavage, reforming nuclear membrane, and disappearing fibers
• Terminology recap for meiosis one:

  • Synapsis: homologous pairs moving together
  • By valence: touching homologous pairs
  • Diploid: full set of chromosomes
  • Haploid: half the number of chromosomes
  • Crossing over: exchange of genetic information between homologous pairs
  • Random arrangement: chromosomes align randomly at the equator
  • Recombinant chromosomes: chromosomes with exchanged genetic information
  • Homologous pair: chromosomes with similar genetic information
  • Chiasmata: point where bivalence touches
  • Cytokinesis: separation of cytoplasm at the end of telophase