Cell Division
malignant tumor
A cancerous tumor that is spreads to neighboring tissue.
cyclin
A cellular protein that occurs in a cyclically fluctuating concentration and that plays an important role in regulating the cell cycle.
chromosome
A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each structure consists of one very long DNA molecule and associated proteins. (A bacterial one usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.)
recombinant chromosome
A chromosome created when crossing over combines the DNA from two parents into a single chromosome.
checkpoint
A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.
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.
karyotype
A display of the chromosome pairs of a cell arranged by size and shape.
cell plate
A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.
Down syndrome
A human genetic disease caused by the presence of an extra chromosome 21; characterized by mental retardation and heart and respiratory defects.
alternation of generations
A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.
clone
A lineage of genetically identical individuals or cells.
benign tumor
A mass of abnormal cells that remains at the site of its origin.
binary fission
A method of asexual reproduction by "division in half." In prokaryotes, the process does not involve mitosis; but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.
meiosis
A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell.
G0 phase
A nondividing state occupied by cells that have left the cell cycle.
homologous chromosomes/homologs/homologous pair
A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One one the corresponding chromosomes is inherited from the organism's father, the other from the mother.
mitosis
A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. The process conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei.
cyclin-dependent kinase (Cdk)
A protein kinase that is active only when attached to a particular cyclin.
growth factor
A protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells.
aster
A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis.
locus
A specific place along the length of a chromosome where a given gene is located.
kinetochore
A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.
sexual reproduction
A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the parents.
mitotic spindle
An assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis.
metaphase plate
An imaginary 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, from its origin in the division of a parent cell until its own division into two.
sister chromatids
Either of two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, the two copies make up one chromosome; the two copies are eventually separated during mitosis or meiosis II.
sporophyte
In organisms (plants and some algae) that have alternation of generations, the multicellular diploid form that results from the union of gametes. It produces haploid spores by meiosis that develop into gametophytes.
gametophyte
In organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes.
spore
In the life cycle of a plant or alga undergoing alternation of generations, a haploid cell produced in the sporophyte by meiosis. It can divide by mitosis to develop into a multicellular haploid individual, the gametophyte, without fusing with another cell.
origin of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
centrosome
Structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubule-organizing center, containing two centrioles.
chiasma
The X-shaped, microscopically visible region where homologous nonsister chromatids have exchanged genetic material through crossing over during meiosis, the two homologs remaining associated due to sister chromatid cohesion.
chromatin
The complex of DNA and associated proteins that makes up a eukaryotic chromosome.
transformation
The conversion of a normal animal cell to a cancerous cell.
cytokinesis
The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.
cleavage furrow
The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate.
asexual reproduction
The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.
life cycle
The generation-to-generation sequence of stages in the reproductive history of an organism.
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.
synapsis
The pairing and physical connection of replicated homologous chromosomes during prophase I of meiosis.
interphase
The period in the cell cycle when the cell is not dividing. During this phase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. The phase accounts for 90% of the cell cycle.
mitotic (M) phase
The phase of the cell cycle that includes mitosis and cytokinesis.
density-dependent inhibition
The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.
cleavage
The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane.
crossing over
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.
anchorage dependence
The requirement that a cell must be attached to a substratum in order to divide.
genetics
The scientific study of heredity and hereditary variation.
prometaphase
The second stage of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.
centromere
The specialized region of the chromosome where two sister chromatids are most closely attached.
metastasis
The spread of cancer cells to locations distant from their original site.
heredity
The transmission of traits from one generation to the next.
