Cell Division - Genetics

The larger the recombination frequency, the larger the distance between two genes. By looking at the data, we know that genes W and X are close to one another. Also, genes X and Y are close to one another. Gene Z, however, seems to be far away from both W and Y (but closer to W). We can represent these distances relatively in a picture:

W - - - X (3)

X - - Y (2)

Y - - - - - - - - - - - - - Z (13)

Z - - - - - - - - W (8)

The most likely explanation is that W, X, and Y are close to one another and Z is located slightly farther away on whichever side W is closest. A spatial map would look something like this:

Z - - - - - - - - - - W - - - X - - Y

The S phase is the "synthesis" phase, where DNA is duplicated. Cells that are not dividing are considered to be in the G0 phase, however, they can enter the cell cycle if they receive the proper signals. The S phase occurs before the M phase (mitosis) as the cell begins to prepare for division.

Apoptosis is the term used to describe programmed cellular death. Apoptosis is useful because it prevents the replication of damaged/mutated cells. p53 is an important signal that when activated, instructs a cell to commit apoptosis. Cancer is partially caused by a failure of the p53 signal, thus allowing for uninterrupted cellular growth.

In metaphase, spindle fibers align chromosomes along the middle of the cell nucleus. A good way to remember this is "M" in metaphase stands for middle. In this portion of mitosis, the cell ensures that each daughter cell will receive the appropriate genetic material. Metaphase occurs right before Anaphase.

The correct order is as follows:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Cytokinesis signals the end of mitosis. In this phase, a fiber ring contracts around each daughter cell (thus making two complete daughter cells).

The nucleolus disappearing is an important part of the cell cycle. This step takes place in prophase. In prophase, chromosomes become visible under the light microscope. They are visible as the chromatin become condensed. There are important facts to remember about prophase.

Diploid means 2_n_, where n is the number of chromosomes in a particular species. If there are 10 chromosomes, there will be 20 chromatids. For each chromosome there are two chromatids. Since this is before the cells have fully divided, there will be 2 times the number of chromosomes during prophase. Therefore, the answer is 20.

The G0 phase is for cell cycle arrest. Cells in this phase are not actively dividing and are not preparing to divide. Being in G0 is technically "outside" of the cell cycle. A cell must receive certain and specific signals to exit the G0 phase and enter the G1 phase (to prepare for replication and division). Cells within the cell cycle might receive certain signals telling them to stop dividing. in this case, a cell will exit the cell cycle and enter the G0 phase.

When the cell moves past the restriction point, it has committed to dividing to form a daughter cell. S phase follows immediately after this point, and the cell begins to duplicate all of the chromosomes comprising its genetic material.

Prophase and metaphase happen before anaphase, and the duplicated chromosomes (sister chromatids) condense and align. During anaphase they are pulled apart and start migrating to opposite cell poles. Telophase and cytokinesis follow anaphase to complete the division of the cell into two new cells.

The mitotic spindle is a long cytoskeletal structure that physically pulls the chromatids apart so that each new cell has a complete set of chromosomes. Centromeres are the location that spindles attach to the chromosomes, and centrioles anchor them in the cell poles. The nucleus and endoplasmic reticulum do not participate in this process.

Cytokinesis is the last processes of cell replication and division and consists of the cell membrane dividing into two.

During Meiosis, the cell starts with 2n in interphase, then duplicates its DNA to have 4n throughout prophase I, metaphase I, and anaphase I. The cell then splits in two during telophase/cytokinesis, and there are 2n during prophase II, metaphase II, and anaphase II. The end product after telophase II is 1n.

While somatic cells in humans are diploid and contain 46 chromosomes total (or 23 pairs), gamete cells are haploid and contain 23 chromosomes. When a gamete, such as an egg, combines with a sperm during fertilization, two haploid cells combined to make one diploid cell called a zygote. This zygote undergoes meiosis and produces the offspring's gametes.

By definition, cytokinesis is the act of cytoplasmic division during cell division, be it during mitosis or meiosis. In the case of mitosis, one somatic cell that has replicated its DNA divides into two daughter cells that genetically identical to the parent cell.

Cyclins combine with CDK to regulate the cell cycle progression, forming active kinases, which phosphorylated the checkpoints. Tumor suppressors can inhibit cyclins and CDK to down regulate growth. Growth factors bind to receptors, which then have their message carried via secondary messangers to transcription factors. Transcription factors may then activtae CDK or cyclins.

G2, or Gap 2 phase, is the third and last subphase of interphase, preceding mitosis. S phase is the phase in which DNA is duplicated and G1 has the first checkpoint. G0 is the phase where cells do not divide anymore, also known as the resting phase.

Interphase is the first stage of cell division and involves the cell going about its normal business. Prophase is when the chromatin bundle up into chromosomes. Anaphase occurs when the sister chromatids separate. Telophase is when the cell pinches, and cytokenisis is when the cell actually seperates. Metaphase is the stage where the sister chromatids line up in the middle of the cell.

The correct answer here is the fiber connecting the chromosomes in the initial stages of mitosis. Remember that during mitosis, 1 pair of chromosomes becomes 2 new pairs. This requires the pair to split initially, duplicate, then break off into the new cells. The last stage of cell division is called anaphase, not a centromere. A centromere is the middle of a pair of chromosomes, not the individual chromosome. If you chose the daughter cell, remember that centromeres are not describing the new cell itself, but the connection between chromosomes inside the cell.