…………………………………………….... reproduction is a characteristic of life....
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Reproduction is a characteristic of life.
Reproduction of individuals depends on the reproduction at the cellular layer
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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
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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.
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The eukaryotic cell cycle has 5 main phases:
1. G1 (gap phase 1)2. S (synthesis)3. G2 (gap phase 2)4. M (mitosis)5. C (cytokinesis)The length of a complete cell cycle
varies greatly among cell types.
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Interphase
G1 growth phase; synthesis of organelles
S synthesis of DNA (replication) G2 growth; synthesis of proteins
essential to cell division -each chromosome in the cell consists of
two identical sister chromatids Cell is preparing to divide
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Mitosis prophase metaphase anaphase telophase
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Mitosis provides cells for growth, cell
replacement, and asexual reproduction maintains chromosome number
Meiosis produces cells for sexual reproduction reduces chromosome number by half
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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 chromosomecentromere - structure by which
chromatids of a dyad chromosome are held together
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Part of the cell cycle where the cell is actually dividing
Nucleus and its contents divide and are evenly distributed forming 2 daughter nuclei
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Prophase: dyad (replicated) chromosomes resemble long threads (chromatin)
replicated centrioles move apart toward opposite poles; (animal cell)
nucleolus disappears; dyad chromosomes condense (coil tightly);
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nuclear membrane disintegrates
spindle fibers appear between centrioles; dyad chromosomes migrate toward the equator of the cell
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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
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2. Metaphase: dyad chromosomes line up along the equator of the cell
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3. Anaphase: dyad chromosomes separate forming monad chromosomes; monad chromosomes move toward opposite poles
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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
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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
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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.
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Mitosis provides cells for growth, cell
replacement, and asexual reproduction maintains chromosome number
Meiosis produces cells for sexual reproduction reduces chromosome number by half
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preceded by interphase which includes chromosome replication
two meiotic divisions four daughter cells produceddaughter cells contain half the
number of chromosomes as the original cell
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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
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Chromosomes are replicated Chromosomes are replicated during S-phase of interphase. As during S-phase of interphase. As a result, monad chromosomes a result, monad chromosomes
become dyad chromosomes.become dyad chromosomes.
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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
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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
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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
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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
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meiosis in males – spermatogenesis
meiosis in females - oogenesis
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4 mature sperm cells produced from meiosis in a single spermatocyte
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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
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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
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• 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.
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• Cells normally hold caspases in check with inhibitors.
• Caspases are released by internal or external signals.
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• 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.
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Carina Perete DVM
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?
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