MEIOSIS

• Sexual reproduction is the fusion of gametes (reproductive cells) from 2 different individuals to produce and offspring with genetic variation.
• Haploid - n

  Diploid - 2n

  Haploid gametes - n = 23
• label cycle

  A) meiosis

  B) sperm (n)

  C) fertilization

  D) diploid zygote

  E) multicellular diploid

  F) 2n = 46

  
• The process of meiosis involves two rounds of cell division, resulting in four haploid daughter cells.
• In meiosis one, it separates homologous chromosomes
• In meiosis two, it separates sister chromatids
• In interphase, the pair of homologous chromosomes in diploid parent cell are replicated, containing sister chromatids.
• During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The pairs of replicated chromosomes are known as sister chromatids, and they remain joined at a central point called the centromere. A spindle also forms from long proteins called microtubules on each side, or pole, of the cell.
• Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination occuring at the chiasmata.
• Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes.
• In metaphase I, the homologous pairs of chromosomes align on either side of the equatorial (metaphase) plate. the spindle fibres on the opposite pole attach to the homologous chromosomes.
• In anaphase I, the spindle fibres contract and pull the homologous pairs, each with two chromatids, away from each other and toward each pole of the cell. the sister chromatids remain attached to centromeres.
• During telophase I, the chromosomes are enclosed in nuclei. The cell now undergoes a process called cytokinesis that divides the cytoplasm of the original cell into two daughter cells. Each daughter cell is haploid and has only one set of chromosomes, or half the total number of chromosomes of the original cell.
• During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells. 
• Then in anaphase II, the chromosomes separate at the centromeres. The spindle fibers pull the separated chromosomes toward each pole of the cell. 
•  Finally, during telophase II, the chromosomes are enclosed in nuclear membranes. Cytokinesis follows, dividing the cytoplasm of the two cells. At the conclusion of meiosis, there are 4 haploid daughter cells.
• Mitosis results in 2 identical daughter cells for growth and repair. Meiosis results in 4 genetically diverse haploid daughters for sexual reproduction.
• Mitosis has 1 round of division and Meiosis has 2
• In mitosis the daughter cells are identical to parent cell and has same number of chromosomes to them. in meiosis, the daughter cells are diverse and it is 1/2 the number of chromosomes to the parents.
• In mitosis, the chromosomes align independently, no chiasmata, centromeres on metaphase plate, chromatids disjoin, 2n=2n.
• In meiosis, chromosomes synapse, there is a chiasmata that is on the metaphase plate, chromosomes disjoin, 2n=n
• label mitosis

  A) prophase

  B) chromosome duplication

  C) 2n=6

  D) duplicated chromosome

  E) metaphase

  F) individual chromosomes line up

  G) Anaphase Telophase

  H) 2 sister chromatids separate

  I) 2n

  
• label meiosis

  A) chiasmata

  B) prophase 1

  C) pair of duplicated homologs

  D) metaphase 1

  E) pairs of homologous chromosomes line up

  F) Anaphase 1 Telophase 1

  G) homologs separate

  H) meiosis 2

  I) sister chromatids separate

  
• Genetic diversiy is important for natural selection, increasing genetic variation, means increasing survival. It allows populations to adapt to environmental conditions. Meiosis allows mutations, gene flow and genetic drift.