Genetic Terms – Binary Fission - Mitosis

Binary Fission • Asexual reproduction

• Cell division

• Prokaryotes

• Each offspring is genetically identical to its parent

• E. coli – under optimal conditions – can complete this process in 20 minutes!

Binary Fission

Step 1: The cell wall prepares for

replication. The cell wall starts to rupture.

Step 2: The cell grows larger and the

chromosomes separate and move to

opposite poles of the cell. The cell

membrane begins to pinch inward,

separating the two identical chromosomes.

Step 3: Cytokinesis occurs and two

identical bacterium exist

Mitosis

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Mitosis

1. Division of the nucleus - Also

called karyo kinesis

2. Only occurs in eukaryotes

3. Has four stages

4. Doesn’t occur in some cells

such as brain cells

Four Mitotic Stages

•Prophase

•Metaphase

•Anaphase

•Telophase

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Early Prophase Chromatin in nucleus condenses to form visible

chromosomes

Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal)

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Chromosomes

Nucleolus Cytoplasm

Nuclear Membrane

Late Prophase

Nuclear membrane & nucleolus are broken down

Chromosomes continue condensing & are clearly visible

Spindle fibers called kinetochores attach to the centromere of each chromosome

Spindle finishes forming between the poles of the cell

Late Prophase

Nucleus & Nucleolus have disintegrated

Chromosomes

Review of Prophase

What’s happening

Sketch The Spindle

Metaphase Chromosomes, attached to the kinetochore fibers, move

to the center of the cell

Chromosomes are now lined up at the equator

Pole of the Cell

Equator of Cell

Metaphase

Chromosomes lined at the Equator

Asters at the poles

Spindle Fibers

Anaphase

Occurs rapidly

Sister chromatids are pulled

apart to opposite poles of the

cell by kinetochore fibers

Anaphase

Sister Chromatids being separated into daughter chromosomes

Anaphase Review

What the cell looks like

What’s occurring

Telophase

Sister chromatids at opposite poles

Spindle disassembles

Nuclear envelope forms around each set of sister chromatids

Nucleolus reappears

CYTOKINESIS occurs

Chromosomes reappear as chromatin

Comparison of Anaphase & Telophase

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Cytokinesis

Means division of the cytoplasm

Division of cell into two, identical halves called daughter cells

In plant cells, cell plate forms at the equator to divide cell

In animal cells, cleavage furrow forms to split cell

Daughter Cells of Mitosis

Have the same number of chromosomes as each other and as the parent cell from which they were formed

Identical to each other, but smaller than parent cell

Must grow in size to become mature cells (G1 of Interphase)

Overview of Mitosis

Occurs in somatic cells

Longitudinal division of replicated chromosomes in one

nucleus to form two genetically identical daughter nuclei.

Each “daughter” nucleus has the same number of

chromosomes (and sets) that the “parent” nucleus had.

Mitosis requires One division.

1 cell 2 cells (called daughter cells)

Daughter cells are genetically identical

Chromosome number does not change.