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 Reproduction is a characteristic of life.  Reproduction of individuals depends on the reproduction at the cellular layer Carina Perete DVM

 From the cell theory, all cells arose from pre existing cells  Nucleus- control center of the cell  Nucleus contains chromosomes which bear the genes  Nucleus carries “blueprint” Carina Perete DVM

 Genes- unit of information passed from generation to generation -determine the characteristics of each new organism and directs its many activities  when the cell divides, the nuclear information must be transmitted in orderly fashion to the new cells Carina Perete DVM

 Bacteria reproduce asexually by binary fission.  A bacterium possesses a single, circular chromosome which is replicated; and then the replicates (chromosomes) are distributed to two new cells formed by division of the original cell. Carina Perete DVM

The eukaryotic cell cycle has 5 main phases: 1. G 1 (gap phase 1) 2. S (synthesis) 3. G 2 (gap phase 2) 4. M (mitosis) 5. C (cytokinesis) The length of a complete cell cycle varies greatly among cell types. Carina Perete DVM

 Interphase  G 1 growth phase; synthesis of organelles  S synthesis of DNA (replication)  G 2 growth; synthesis of proteins essential to cell division  -each chromosome in the cell consists of two identical sister chromatids  Cell is preparing to divide Carina Perete DVM

 Mitosis  prophase  metaphase  anaphase  telophase Carina Perete DVM

 Mitosis  provides cells for growth, cell replacement, and asexual reproduction  maintains chromosome number  Meiosis  produces cells for sexual reproduction  reduces chromosome number by half Carina Perete DVM

 chromatin - the form taken by chromosomes when a eukaryotic cell is not dividing  monad chromosome - unreplicated chromosome (single chromosome)  dyad chromosome - replicated chromosome (double chromosome)  chromatid - half of a dyad chromosome  centromere - structure by which chromatids of a dyad chromosome are held together Carina Perete DVM

 Part of the cell cycle where the cell is actually dividing  Nucleus and its contents divide and are evenly distributed forming 2 daughter nuclei Carina Perete DVM

Prophase: dyad (replicated) chromosomes resemble long threads (chromatin)  replicated centrioles move apart toward opposite poles; (animal cell)  nucleolus disappears; dyad chromosomes condense (coil tightly); Carina Perete DVM

 nuclear membrane disintegrates  spindle fibers appear between centrioles; dyad chromosomes migrate toward the equator of the cell Carina Perete DVM

Prometaphase: -chromosomes become attached to the spindle apparatus by their kinetochores -a second set of microtubules is formed from the poles to each kinetochore -microtubules begin to pull each chromosome toward the center of the cell Carina Perete DVM

 2. Metaphase: dyad chromosomes line up along the equator of the cell Carina Perete DVM

 3. Anaphase: dyad chromosomes separate forming monad chromosomes; monad chromosomes move toward opposite poles Carina Perete DVM

 4. Telophase: monad chromosomes cluster at poles; cytokinesis occurs gradually; nuclear membrane forms; nucleolus reappears; chromosomes uncoil; cytokinesis is completed; two daughters cells are formed Carina Perete DVM

Cytokinesis – cleavage of the cell into equal halves -in animal cells – constriction of actin filaments produces a cleavage furrow -in plant cells – plasma membrane forms a cell plate between the nuclei -in fungi and some protists – mitosis occurs within the nucleus; division of the nucleus occurs with cytokinesis Carina Perete DVM

 have the same number of chromosomes as each other and as the original cell from which they were formed  e.g. Mitosis in a cell which possesses 4 chromosomes will result in the formation of two daughter cells each having 4 chromosomes. Carina Perete DVM

 Mitosis  provides cells for growth, cell replacement, and asexual reproduction  maintains chromosome number  Meiosis  produces cells for sexual reproduction  reduces chromosome number by half Carina Perete DVM

 preceded by interphase which includes chromosome replication  two meiotic divisions  four daughter cells produced  daughter cells contain half the number of chromosomes as the original cell Carina Perete DVM

 monad chromosome - unreplicated chromosome  dyad chromosome - chromosome composed of two chromatids (replicates)  homologous - similar in size and shape  synapsis - pairing of homologous chromosomes  crossover - exchange of segments between chromatids of homologous chromosomes Carina Perete DVM

Chromosomes are replicated during S-phase of interphase. As a result, monad chromosomes become dyad chromosomes. Chromosomes are replicated during S-phase of interphase. As a result, monad chromosomes become dyad chromosomes. Carina Perete DVM

 Prophase I: homologous chromosomes of diploid cell synapse; homologous pairs migrate toward equator of cell; crossover may occur during synapsis  Metaphase I: dyad pairs of homologous chromosomes align at the equator of the cell Carina Perete DVM

 Anaphase I: homologous chromosomes move apart toward opposite poles  Telophase 1: chromosomes cluster at poles of cell; cytokinesis occurs forming two haploid daughter cells each containing one member of each homologous pair thus reducing chromosome by half Carina Perete DVM

 Prophase II: dyad chromosomes move toward the equator of each cell (2)  Metaphase II: dyad chromosomes align at equator of cell  Anaphase II: dyad chromosomes separate forming monad chromosomes (chromatids separate); monads migrate toward opposite poles of each cell Carina Perete DVM

 Telophase II: cytokinesis occurs at right angles to the first plane of division in each cell (2); four daughter cells are formed each having half the number of chromosomes as the original cell Carina Perete DVM

 meiosis in males – spermatogenesis  meiosis in females - oogenesis Carina Perete DVM

 4 mature sperm cells produced from meiosis in a single spermatocyte Carina Perete DVM

 one mature ovum (egg cell) and 3 polar bodies formed from meiosis in a single oocyte  human female embryo - oocytes formed by mitosis and then complete prophase I of meiosis by time of birth  puberty - one oocyte in alternating ovaries resumes meiosis under the influence of hormones; at ovulation the oocyte is at metaphase II  oogenesis will be completed in the event of fertilization Carina Perete DVM

 Mitosis  synapsis does not occur  one division occurs  two daughter cells are formed  chromosome number is maintained  Meiosis  synapsis occurs during Prophase I  two divisions occur  four daughter cells are formed  chromosome number is reduced by half Carina Perete DVM

Apoptosis is programmed cell death and involves a sequence of cellular events involving: fragmenting of the nucleus, blistering of the plasma membrane, and engulfing of cell fragments by macrophages and/or neighboring cells. Apoptosis and cell division are balancing processes that maintain the normal level of somatic (body) cells. Carina Perete DVM

Cells normally hold caspases in check with inhibitors. Caspases are released by internal or external signals. Carina Perete DVM

Cell death is a normal and necessary part of development: frogs, for example, must destroy tail tissue they used as tadpoles, and the human embryo must eliminate webbing found between fingers and toes. Death by apoptosis prevents a tumor from developing. Carina Perete DVM

1. In what stage of your cell cycle does your DNA replicate? 2. How many cells are produced in binary fission of your bacterial cell? 3. What stage of your cell cycle is responsible for active dividing of your cell? 4. What type of cellular reproduction produces gametes for sexual reproduction? 5. What is the term for programmed cell death? Carina Perete DVM