Cellular reproduction Reproduction is a characteristic of life

Reproduction is a characteristic of life. Reproduction of individuals depends on the reproduction

review From the cell theory, all cells arose from pre existing cells Nucleus- control

Genes- unit of information passed from generation to generation -determine the characteristics of

Asexual Reproduction in Bacteria reproduce asexually by binary fission. A bacterium possesses a single,

The eukaryotic cell cycle has 5 main phases: 1. G 1 (gap phase 1)

The Eukaryotic Cell Cycle Interphase G 1 growth phase; synthesis of organelles S synthesis

Mitosis prophase metaphase anaphase telophase Carina Perete DVM

Types of Cell Division Mitosis provides cells for growth, cell replacement, and asexual reproduction

Important Terms chromatin - the form taken by chromosomes when a eukaryotic cell is

Mitosis* Part of the cell cycle where the cell is actually dividing Nucleus and

Prophase: dyad (replicated) chromosomes resemble long threads (chromatin) replicated centrioles move apart toward opposite

nuclear membrane disintegrates spindle fibers appear between centrioles; dyad chromosomes migrate toward the

Promethaphase Prometaphase: -chromosomes become attached to the spindle apparatus by their kinetochores -a second

Mitosis* 2. Metaphase: dyad chromosomes line up along the equator of the cell Carina

Mitosis* 3. Anaphase: dyad chromosomes separate forming monad chromosomes; monad chromosomes move toward opposite

Mitosis* 4. Telophase: monad chromosomes cluster at poles; cytokinesis occurs gradually; nuclear membrane forms;

cytokinesis Cytokinesis – cleavage of the cell into equal halves -in animal cells –

Daughter Cells of Mitosis have the same number of chromosomes as each other and

Meiosis preceded by interphase which includes chromosome replication two meiotic divisions four daughter cells

Important terms in the study of meiosis monad chromosome - unreplicated chromosome dyad chromosome

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

Meiosis I Prophase I: homologous chromosomes of diploid cell synapse; homologous pairs migrate toward

Anaphase I: homologous chromosomes move apart toward opposite poles Telophase 1: chromosomes cluster

Meiosis II (resembles mitosis) Prophase II: dyad chromosomes move toward the equator of each

Telophase II: cytokinesis occurs at right angles to the first plane of division

Gamete formation - meiosis in males – spermatogenesis meiosis in females - oogenesis Carina

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

Oogenesis one mature ovum (egg cell) and 3 polar bodies formed from meiosis in

Comparison of Mitosis and Meiosis Mitosis synapsis does not occur one division occurs two

Apoptosis is programmed cell death and involves a sequence of cellular events involving: •

Cells normally hold caspases in check with inhibitors. • Caspases are released by internal

Cell death is a normal and necessary part of development: frogs, for example, must

quiz 1. 2. 3. 4. 5. In what stage of your cell cycle does

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Cellular reproduction ………………………. . .

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

review 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

Asexual Reproduction in 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

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

The Eukaryotic Cell Cycle 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

Carina Perete DVM

Types of Cell Division 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

Important Terms 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

Carina Perete DVM

Mitosis* 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

Carina Perete DVM

Promethaphase 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

Carina Perete DVM

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

Carina Perete DVM

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

Carina Perete DVM

Mitosis* 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

Carina Perete DVM

cytokinesis 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

Carina Perete DVM

Daughter Cells of Mitosis 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

Meiosis 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

Important terms in the study of meiosis 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

Carina Perete DVM

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

Meiosis I 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

Carina Perete DVM

Meiosis II (resembles mitosis) 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

Gamete formation - meiosis in males – spermatogenesis meiosis in females - oogenesis Carina Perete DVM

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

Oogenesis 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

Comparison of Mitosis and Meiosis Mitosis synapsis does not occur one division occurs two daughter cells are formed chromosome number is maintained synapsis occurs during Prophase I two divisions occur four daughter cells are formed chromosome number is reduced by half Meiosis 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

Carina Perete DVM

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