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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.

Carina Perete DVM

Carina Perete DVM

Carina Perete DVM

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

Carina Perete DVM

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

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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

Carina Perete DVM

Carina Perete DVM

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

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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

Carina Perete DVM

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

Carina Perete DVM

Carina Perete DVM

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

Carina Perete DVM

Carina Perete DVM

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

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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

Carina Perete DVM

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

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.

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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

Carina Perete DVM

Carina Perete DVM

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

Carina Perete DVM

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

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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.

Carina Perete DVM

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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