3 Meiosis

• MEIOSIS

  ● Occurs in the germ cells of an organism

  ● Produces four daughter cells which are

  genetically different

  ● Cells has a chromosome value of n

  ● Divided into 4 stages: Interphase,

  ● Meiosis I, Meiosis II, Cytokinesis
• MEIOSIS I

  ● Enables the synapsis and recombination of

  homologous chromosomes

  ● Reductional division

  ● Chromosomes will start in the form of the

  tetrads which will eventually end as sister

  chromatids

  ● Divided into four different subphases:

  Prophase I,
• PROPHASE I

  ● Chromosomes will start to condense

  ● Homologous chromosomes will synapse and

  will allow crossing over

  ● Nuclear envelope disappears and spindle

  fibers will start to from

  ● Divided into five different subphases:

  Leptotene, Zygotene, Pachytene, Diplotene,

  and Diakinesis
• Leptotene

  ● Contraction of chromosomes

  ● The chromosomes become visible

  ● Chromosomes will start to look for its

  homologous pair

  
• Zygotene

  ● Pairing up and cohering of homologous

  chromosomes

  ● Tetrads will start to form

  ● Synaptonemal complex will start to form

  
• Pachytene

  ● Tetrads are now more visible

  ● Three part synaptonemal complex is formed

  ● Crossing over will take place

  
• Diplotene

  ● Tetrads will start to separate

  ● Chiasma will start to form

  ● The result of crossing over is evident

  
• Diakinesis

  ● Chiasma will move at the ends of the

  chromosomes

  ● Tetrads will remain attached at the chiasma

  ● Final stages of chromosome condensation

  
• METAPHASE I

  ● The centrosomes have reached the opposite

  poles of the cell

  ● Homologous chromosomes will align at the

  metaphase plate

  ● The spindle fibers are now attached to the

  kinetochores of the chromosomes

  
• ANAPHASE

  ● The spindle fibers will start to shorten, pulling

  the homologous chromosomes apart

  ● The nonkinetochore spindles will lengthen as

  the kinetochore spindles shorten

  ● The cell will start to elongate

  
• TELOPHASE

  ● The chromosomes reach the opposite poles of

  the cell

  ● The nuclear envelope of the cell will start to

  reform

  ● Cell will immediately enter a short interphase

  stage

  ● No replication of DNA will be done in the

  short interphase

  
• MEIOSIS II

  ● The whole process is similar to that of mitosis

  ● Produces 4 daughter cells with a chromosome

  count of n

  ● Divided into four different subphases:

  Prophase II, Metaphase II, Anaphase II, and

  Telophase II
• PROPHASE

  ● Chromosomes will start to condense The

  centrosomes form asters and release

  microtubules (spindles) Centrosomes will start

  to migrate to the opposite poles The nuclear

  envelope will start to disappear

  
• FORMATION OF THE SEX CELLS

  ● The sex cells (gametes) are the end product of

  meiosis

  ● Male sex cells are produced in the testes while

  female sex cells are produced in the ovaries

  ● Sperm cell production is known as

  spermatogenesis while egg cell production is

  known as oogenesis

  
• FORMATION OF THE SEX CELLS