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the third stage of mitosis, beginning when sister chromatids separate from each other and ending when a complete set of daughter chromosomes have arrived at each of the two poles of the cell

asexual reproduction

the creation of offspring by a single parent, without the participation of sperm and egg


a chromosome not directly involved in determining the sex of an organism: in mammals, for example, any chromosome other than X or Y

binary fission

a means of asexual reproduction in which a parent organism, often a single cell, divides into two individuals of about equal size

cell cycle

an orderly sequence of events (including interphase and the mitotic phase) from the time a eukaryotic cell divides to form two daughter cells to the time those daughter cells divide again

cell cycle control system

a cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle


the region of a chromosome where two sister chromatids are joined and where spindle microtubules attack during mitosis and meiosis. the centromere divides at the onset of anaphase during mitosis and anaphase II of meiosis


the combination of DNA and proteins that constitute chromosomes; often used to refer to the diffuse, very extended form taken by the chromosomes when a eukaryotic cell is not dividing


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. Chromosomes consist of chromatin

crossing over

the exchange of segments between chromatids of homologous chromosomes during synapsis in prophase I of meiosis; also, the exchange of segments between DNA molecules in prokaryotes


the division of the cytoplasm to form two separate daughter cells. Cytokinesis usually occurs during telophase of mitosis, and the two processes make up the mitotic (M) phase of the cell cycle


the loss of one or more nucleotides from a gene by mutation; the loss of a fragment of a chromosome

diploid cell

in an organism that reproduces sexually, a cell containing two homologous sets of chromosomes, one set inherited from each parent; a 2n cell

Down syndrome

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


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


the union of the nucleus of a sperm cell with the nucleus of an egg cell, producing a zygote


a sex cell; a haploid egg or sperm. The union of two gametes of opposite sex (fertilization) produces a zygote

haploid cell

in the life cycle of an organism that reproduces sexually, a cell containing a single set of chromosomes; an n cell

homologous chromosomes

the two chromosomes that make up a matched pair in a diploid cell. have the same length, same centromere position and staining pattern and possess genes for the same characteristics at corresponding loci. one homologous chromosome is inherited from the mother, one from the father. in humans, 23 types, each with different sets of genes. make a total of 46 chromosomes (23 pairs). the two homologous chromosomes may differ in the VERSION of the genes they carry


the period in the eukaryotic cell cycle when the cell is not actually dividing


a change in a chromosome resulting from reattachment in a reverse direction of a chromosome fragment to the original chromosome. mutagens and errors during meiosis can cause inversions


a display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere position


the particular site where a gene is found on a chromosome. homologous chromosomes have corresponding gene loci


in a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter nuclei. meiosis and cytokinesis produce haploid gametes from diploid cells in the reproductive organs of the parents


the second stage of mitosis. during metaphase, all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle


the spread of cancer cells beyond their original site


the division of a single nucleus into two genetically identical daughter nuclei. mitosis and cytokinesis make up the mitotic (M) phase of the cell cycle

mitosis (M) phase

the part of the cell cycle when mitosis divides the nucleus and distributes its chromosomes to the daughter nuclei, and cytokinesis divides the cytoplasm, producing two daughter cells

mitotic spindle

a spindle-shaped structure formed of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis and meiosis


an accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase. can create gametes with too many or too few sex chromosomes


the first stage of mitosis, during which duplicated chromosomes condense to form structures visible with a light microscope and the mitotic spindle forms and begins moving the chromosomes toward the center of the cell

sex chromosomes

a chromosome that determines whether an individual is male or female

sexual reproduction

the creation of offspring by the fusion of two haploid sex cells (gametes) forming a diploid zygote

sister chromatid

one of the two identical parts of a duplicated chromosome in a eukaryotic cell

somatic cell

any cell in a multicellular organism except a sperm or egg cell or a cell that develops into a sperm or egg


the fourth and final stage of mitosis, during which the daughter nuclei form at the two poles of a cell. Telophase usually occurs together with cytokinesis


a paired set of homologous chromosomes, each composed of two sister chromatids. tetrads form during prophase I of meiosis


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

trisomy 21

error in meiosis (nondisjunction) produces a gamete (generally an egg) with two copies of chromosome 21 n = 24 rather than 23. if the abnormal gamete combines with a normal gamete (n=23) the zygote will have 47 total chromosomes


an abnormal mass of cells that forms within otherwise normal tissue


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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