1. Grows.
2. Prepares for division.
3. Divides to form two genetically identical daughter cells.

G1

S

G2

• Prophase
• Metaphase
• Anaphase
• Telophase

1. DNA in form of chromotids, unorganized
2. DNA wraps around histone protein twice, now called nucleosomes
3. Nucleosomes are further wrapped into a solenoid (a coil of nucleosomes)
4. Solenoids are grouped together in looped "domains" and coil to produce a chromsome

1. Chromatin fibers become more tightly coiled to form chromosomes 
2. THE NUCLEAR ENVELOPE DISSOLVES
3. Mitotic spindle forms and elongates from centrosome regions
4. Spindle microtubules enter the nucleus and attach to chromosomes (kinetochore attatches to spindle)
5. Centrosomes move toward opposite poles of cell due to lengthening microtubles

1. Chromosomes are moved to the metaphase plate (center)
2. The chromosome's centromeres lie on the metaphase plate
3. the spindle microtubles push from opposite poles equally. This causes the movement of chromosomes.
4. centrosomes are at opposite poles

1. Two sister chromatids of each chromosome split
2. chromatids are now chromosomes and move toward opposite poles of the cell
3. Chromatid movement is due to shortening of the spindle microtubules
4. Each pole of the cell has complete, identical set of chromosomes

Six things that occur in Telophase

1. All chromosomes have reached the poles
2. the nuclear membrane re-forms around each set of chromosomes
3. the chromosomes start to elongate to form chromatin (uncoiled chromosome)
4. the nucleoli reappear
5. the spindle apparatus disappears
6. the cell is elongated and ready for cytokinesis

what is cytokinesis in animal cells?

what is cytokinesis in plant cells?

animal cells: an inward pinching of plasma membrane occurs and forms a cleavage furrow

plant cells: a cell plate will form from the inside producing rigid cell walls

two genetically identical cells.

cell growth, embryonic development, tissue repair, and asexual reproduction all include mitosis

How is cell division regulated?

Examples?

proteins called cyclins

Internal regulators (respond to events inside cell, allow cell to proceed only when certain processes have happened inside cell)

External regulators (respond to events outside cell, direct cells to speed up or slow down the cell cycle, ie growth factors)

uncontrolled cell division

• leads to cancers (tumors)
• cancer cells do not respond to the signals that regulate the growth of most cells
• cancer cells can occur in any organ or tissue
• damaged p-63 gene: many cancer patients have

to produce four haploid daughter cells

cell must divide two times

meosis I

• makes two cells with a single set of chromosomes each

and Meiosis II

• teh two cells from Meiosis I will divide to make a total of four cells

1. Chromosomes become visible as the DNA becomes more compact
2. homologous chromosomes are attatched to each other and pair up
3. crossing over occurs
4. spindle microtubules grow from each pole to the equator as in mitosis
5. Nuclear membrane disappears

1. pairs of homologous chromosomes line up across the metaphase plate/equator
2. spindle microtubules from the two poles atttach to different chromosomes in each pair, ensuring that one is puilled to one pole and the other is pulled to the opposite pole

1. Spindle fibers from the poles attach to homologous chromosomes and pull them to opposite poles of the cell. this halves the chromosome number, creating a haploid cell
2. each chromosomes consists of 2 chromotids still

1. Spindle fibers disintegrate
2. the chromosomes uncoil and a new nuclear membrane forms

cytokinesis

• cell splits into two separate cells
• cells are haploid cells
• no S phase is necessary
• Meiosis II needs to occur to separate the sister chromotids

• DNA condenses into visible chromosomes again
• New meiotic spindle fibers grow from the poles to the equators

1. Nuclear membrane disintegrates
2. the individual chromosomes line up along the metaphase plate of the cell
3. spindle fibers from opposite poles attach to each of the sister chromatids at the centromere

1. Centromeres of each chromosome split, releasing each sister chromatid as an individual chromosomes
2. the spindle fibers pull individual chromatids to opposite ends of the cell
3. then cleavage furrow or cell plate

Chromosomes unwind their strands of DNA

Nuclear envelope forms around each of the four haploid cells

chromosomes may not separate when expected to during first of second meiotic division

This results in an unequal distribution of chromosomes

unequaltrivution is due to non-disjunction

the process where two or more homologous chromosomes stick together rather than separating during meiosis.

can lead to changes in chromsomes number

example: down's syndrome (trisomy 21)

chromosome 21 has three copies instead of two

two processes

1. Chorionic Villisampling

• cells are incubated, stained, and prepared on a glass slide
• photomicrograph images are obtained of the chromosomes during mitotic metaphase
• the images are cut out and separated into pairs
• the images of each pair of chromosomes are placed in order by size and the position of their centromeres

to determine:

• prenatal diagnosis of chromosome abnormalities
• gender
• whether non disjunction has occured