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translocation
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A change in a chromosome resulting from a chromosomal fragment attaching to a nonhomologous chromosome; can occur as a result of an error in meiosis or from mutagenesis.
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gamete
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A sex cell; a haploid egg or sperm. The union of two of these cells of opposite sex (fertilization) produces a zygote.
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genetic recombination
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The production, by crossing over and/or independent assortment of chromosomes during meiosis, of offspring with allele combinations different from those in the parents. The term may also be used more specifically to mean the production by crossing over of eukaryotic or prokaryotic chromosomes with gene combinations different from those in the original chromosomes.
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genome
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A complete (haploid) set of an organism's genes; an organism's genetic material.
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haploid cell
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In the life cycle of an organism that reproduces sexually, a cell containing a single set of chromosomes; an n cell.
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autosome
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A chromosome not directly involved in determining the sex of an organism; in mammals, for example, any chromosome other than X or Y.
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cytokinesis
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The division of the cytoplasm to form two separate daughter cells; usually begins during telophase of mitosis; part of the mitotic (M) phase of the cell cycle.
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leukemia
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A type of cancer of the blood-forming tissues, characterized by an excessive production of white blood cells and an abnormally high number of them in the blood; cancer of the bone marrow cells that produce leukocytes.
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mitosis
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The division of a single nucleus into two genetically identical daughter nuclei; part of the mitotic (M) phase of the cell cycle.
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meiosis
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In a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter nuclei; produces haploid gametes from diploid cells in the reproductive organs of the parents.
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fertilization
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The union of the nucleus of a sperm cell with the nucleus of an egg cell, producing a zygote.
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nondisjunction
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An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.
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prophase
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The first stage of mitosis, during which the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still intact.
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zygote
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The fertilized egg, which is diploid, that results from the union of a sperm cell nucleus and an egg cell nucleus.
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life cycle
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The entire sequence of stages in the life of an organism, from the adults of one generation to the adults of the next.
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metastasis
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The spread of cancer cells beyond their original site.
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cell cycle
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An ordered sequence of events (including interphase and the mitotic phase) that extends from the time a eukaryotic cell is first formed from a dividing parent cell until its own division into two cells.
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deletion
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The loss of one or more nucleotides from a gene by mutation; the loss of a fragment of a chromosome.
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trisomy 21
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Another name for Down syndrome.
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anaphase
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The fourth stage of mitosis, beginning when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell.
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cell cycle control system
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A cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle.
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chromatin
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The complex of DNA and proteins that constitutes eukaryotic chromosomes; often used to refer to the diffuse, very extended form taken by chromosomes when a cell is not dividing.
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chiasma
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The microscopically visible site where crossing over has occurred between chromatids of homologous chromosomes during prophase I of meiosis.
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prometaphase
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The second stage of mitosis, during which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids.
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Lymphoma
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Cancer of the tissues that form white blood cells.
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binary fission
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A means of asexual reproduction in which a parent organism, often a single prokaryotic cell, divides into two individuals of about equal size.
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tumor
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An abnormal mass of cells that forms within otherwise normal tissue.
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benign tumor
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An abnormal mass of cells that remains at its original site in the body.
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anchorage dependence
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The requirement that to divide, a cell must be attached to a solid surface.
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asexual reproduction
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The creation of offspring by a single parent, without the participation of sperm and egg.
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cleavage furrow
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The first sign of cytokinesis during cell division in an animal cell; a shallow groove in the cell surface near the old metaphase plate.
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tetrad
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A paired set of homologous chromosomes, each composed of two sister chromatids; form during prophase I of meiosis.
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cell plate
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A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.
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homologous chromosomes
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The two chromosomes that make up a matched pair in a diploid cell. They are of the same length, centromere position, and staining pattern and possess genes for the same characteristics at corresponding loci. One is inherited from the organism's father, the other from the mother.
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cell division
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The reproduction of a cell.
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sister chromatids
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One of the two identical parts of a duplicated chromosome in a eukaryotic cell.
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centromere
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The region of a duplicated chromosome where two sister chromatids are joined and where spindle microtubules attach during mitosis and meiosis.
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crossing over
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The exchange of segments between chromatids of homologous chromosomes during synapsis in prophase I of meiosis.
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centrosome
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Material in the cytoplasm of a eukaryotic cell that gives rise to microtubules; important in mitosis and meiosis; also called microtubule-organizing center; the spindle grows from this structure.
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cleavage
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Cytokinesis in animal cells and in some protists, characterized by pinching in of the plasma membrane.
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inversion
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A change in a chromosome resulting from reattachment of a chromosome fragment to the original chromosome, but in a reverse direction. Mutagens and errors during meiosis can cause this.
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somatic cell
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Any cell in a multicellular organism except a sperm or egg cell or a cell that develops into a sperm or egg; "body cells."
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Down syndrome
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A human genetic disorder resulting from the presence of an extra chromosome 21; characterized by heart and respiratory defects and varying degrees of mental retardation.
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locus
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The particular site where a gene is found on a chromosome.
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duplication
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Repetition of part of a chromosome resulting from fusion with a fragment from a homologous chromosome; can result from an error in meiosis or from mutagenesis.
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chromosome
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A threadlike, gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell; consists of chromatin, a combination of DNA and protein.
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sex chromosome
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A chromosome that determines whether an individual is male or female.
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growth factor
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A protein secreted by certain body cells that stimulates other cells to divide.
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metaphase
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The third stage of mitosis, during which all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle.
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mitotic spindle
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A football-shaped structure formed of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis and meiosis.
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mitotic (M) phase
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The part of the cell cycle when the nucleus is divided (via mitosis), its chromosomes are distributed to the daughter nuclei, and the cytoplasm divided (via cytokinesis), producing two daughter cells.
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karyotype
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A display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere position.
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diploid cell
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In an organism that reproduces sexually, a cell containing two homologous sets of chromosomes, one set inherited from each parent; a 2n cell.
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telophase
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The fifth and final stage of mitosis, during which daughter nuclei form at the two poles of a cell; usually occurs together with cytokinesis.
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carcinoma
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Cancer that originates in the coverings of the body, such as skin or the lining of the intestinal tract.
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density-dependent inhibition
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The arrest of cell division that occurs when cells grown in a laboratory dish touch one another.
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interphase
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The period in the eukaryotic cell cycle when the cell is not actually dividing; constitutes the majority of the time spent in the cell cycle.
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sexual reproduction
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The creation of offspring by the fusion of two haploid sex cells (gametes), forming a diploid zygote.
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sarcoma
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Cancer of the supportive tissues, such as bone, cartilage, and muscle.
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malignant tumor
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An abnormal tissue mass that can spread into neighboring tissue and to other parts of the body; a cancerous tumor.
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