Cleavage-(1)The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2)The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells.

Cytokinesis-The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.

S phase-The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

Gamete-A haploid reproductive cell, such as an egg or a sperm, that is formed by meiosis or is the descendant of the cells formed by meiosis. Gametes unite during sexual reproduction to produce a diploid zygote.

Somatic cell-Any cell in a multicellular organism except a sperm or egg or their precursors.

Growth Factor-A local regulator that acts on nearby cells to stimulate cell proliferation and differentiation.

Benign Tumor-A mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the tumor’s origin.

Interphase-The period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase often accounts for about ‘0% of the cell cycle.

Mitosis-A process of nuclear division in eukaryotic cells conventionally divided into five stages prophase, prometaphase, metaphase, anaphase and telophase. Mitosis conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei.

Chromosome-A cellular structure consisting of one DNA molecule and associated protein molecules. (In some contexts, such as genome sequencing, the term may refer to the DNA alone.); A eukaryotic cell typically has multiple, linear chromosomes,which are located in the nucleus; A prokaryotic cell often has a single, circular chromosome, which is found in the nucleoid, a region that is not enclosed by a membrane.

Centromere-In a duplicated chromosome, the region on each sister chromatid where it is most closely attached to its sister chromatid by proteins that bind to the centromeric DNA. Other proteins condense the chromatin in that region, so it appears as a narrow waist on the duplicated chromosome. (An unduplicated chromosome has asingle centromere, identified by the proteins bound there.)

Cell Division-The production of cells.

Metastasis-The spread of cancer cells to locations distant from their original site.

Mitotic Spindle-An assemblage of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis.

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.

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.

Binary Fission-A method of asexual reproduction in single-celled organisms in which the cell grows to roughly double its size and then divides into two cells. In prokaryotes, binary fission does not involve mitosis, but in single-celled eukaryotes that undergo binary fission, mitosis is part of the progress.

Checkpoint-A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.

Cell Cycle-An ordered sequence of events in the life of the cell, from its origin in the division of the parent cell until its own division into two. The eukaryotic cell cycle is composed of interphase (including G1, S and G2 phases) and M phase (including mitosis and cytokinesis).

Mitotic (M) Phase-The phase of the cell cycle that includes mitosis and cytokinesis.

Genome-The genetic material of an organism or virus; the complete complement of an organism’s or virus’s genes along with its noncoding nucleic acid sequences.

Cell Plate-A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis.

Anchorage Dependence-The requirement that a cell must be attached to a substratum in order to initiate cell division.

Cell Cycle Control System-A cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle.

Origin of Replication-Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides. Sister Chromatids Two copies of a duplicated chromosome Attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, two sister chromatids make up one chromosome. Chromatids are eventually separated during mitosis or meiosis II.

G1 Phase-The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.

Density Dependent Inhibition-The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.

Chromatin-The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

Prophase-The first stage of mitosis, in which chromatin condenses into discrete chromosomes visible with a light microscope, the mitotic spindle begins to form, and the nucleolus disappears but the nucleus remains intact.

Telophase-The fifth and final stage of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun.

G0 Phase-A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.

Prometaphase-The second stage of mitosis, in which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the chromosomes.

Cleavage Furrow-The first sign of cleavage in an animal cell; a shallow groove around the cell in the cell surface near the old metaphase plate.

Anaphase-The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.

Transformation-(1)The process by which a cell in culture acquires the ability to divide indefinitely, similar to the division of cancer cells. (2)A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.

Kinetochore-A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.

G2 Phase-The second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.

Malignant Tumor-A cancerous tumor containing cells that have significant genetic and cellular changes and are capable of invading and surviving in new sites. Malignant tumors can impair the functions of one or more organs.

Metaphase-The third stage of mitosis, in which the spindle is complete and the chromosomes, attached to the microtubules at their kinetochores, are all aligned at the metaphase plate.