Mitosis and Meiosis

interphase

A cell stays at this point 90% of the time. NOT a "resting" phonse for the cell. The cell carries out metabolic processes and prepares for cell division during this phase.

Mitosis

A process that divides the nucleus of a cell. Purpose is to create two daughter cells with identical information. Each daughter cell receives the exact same # and type of chromosomes Consists of 4 phases

Centrosome

A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles.

Metaphase plate

An imaginary structure located at a plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromosomes are located.

Cell Cycle

An ordered sequence of events in the life of a cell

Sister Chromatids

Are the two identical halves of a single chromosome. They are joined together by a centromere.

Crossing over

Homologous Chromosomes (matching chromosomes from mom and dad) join up together and sometimes share genetic information. Happens during stage 2, Prophase I.

G1 Phase

The first gap, or growth phase of the cell cycle. Cellular contents, excluding the chromosomes, are duplicated.

Prophase

The first stage of mitosis. Nuclear membrane disappears. Centrioles appear and begin to move to the opposite ends of the cell. Spindle fibers form between the poles.

Telophase

The fourth and final stage of mitosis. Two new nuclei form. Chromosomes appear as chromatin. Mitosis ends

Meiosis

Creates 4 haploid gamete cells from a diploid cell.

Interphase

At this point the DNA is in its chromatin form and the DNA replicates.

Anaphase I

At this point the spindle fibers start to pull on the chromosomes and each homologous chromosome heads towards a different pole.

Cytokinesis

Cell membrane moves inward to create two separate daughter cells - each with its own nucleus with identical chromosomes.

Clevage

Cell's cytoplasm start to divide. This is part of the Telophase I and Telophase II stages.

Telophase I

Chromosomes are now at the pole, nuclear membranes start to form around the chromosomes, and the chromosomes start to unwind back into chromatin. Cytokinesis occurs and the two cells split. These two cells are still diploid at this point. The next 4 phases occur to each of these cells.

Homologous Chromosomes

Matching chromosomes from mom and dad.

Prophase II

Notice that we skip interphase this time around because there is no replication of DNA between Meiosis I and Meiosis II. At this point the chromosomes reorganize and the nuclear membranes start to dissolve again. Sister chromatids are again joined by a centromere. Spindles start to reform between centrosomes.

Telophase II

Nuclear membranes start to form around the chromosomes again. A cleavage forms. Cytokinesis occurs and the two diploid cells have now divided into 4 haploid cells. In males this equals 4 sperm. In females this creates 1 egg and 3 polar bodies which are useless in humans.

Four phases of Mitosis

Prophase, Metaphase, Anaphase, Telophase

Metaphase I

Spindle fibers are completely formed and attach to the centromeres of the homologous chromosomes. The chromosomes line up down the middle of the spindles along with their homologous pair.

Metaphase II

Spindles are fully formed again and attach to the centromeres. The chromosomes line up down the middle of the spindles.

Prophase I

The DNA starts to coil itself up into visible chromosomes. The copies of each chromosome (sister chromatids) are connected together by a centromere. During the end of this stage the nuclear membrane starts to dissolve, centrosomes move towards the poles, and spindle fibers start to form. Crossing over occurs during this stage.

Cell Division

The reproduction of cells

G2 Phase

The second gap, or growth phase, of the cell cycle. The cell "double checks" the duplicated chromosomes for error, making any needed repairs.

Metaphase

The second stage of mitosis. Chromatids attach to the spindle fibers

Anaphase II

The spindles pull the sister chromatids apart. Each goes towards a different pole.

S Phase

The synthesis phase of the cell cycle; Each of the 46 chromosomes (in humans) is duplicated by the cell. DNA is replicated.

Chromosomes

The things that make organisms what they are. They carry all of the information used to help a cell grow, thrive and reproduce. They are made up of DNA.

Anaphase

The third stage of mitosis. Chromatids of each chromosome separate and the daughter chromosomes are moving to the opposite ends of the cell.

Cytokinesis

This process is part of the Telophase and Telophase II.

Chromatin

Uncoiled chromosomes (loose strands)

Chromatin

thread like structures containing all genetic information (only "appears" during Interphase)