Biology Chapter 8: The Cellular Basis of Reproduction and Inheritance

cell division

The reproduction of a cell through duplication of the genome and division of the cytoplasm.

chromosome

A threadlike, gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis. It consists of one very long piece of chromatin.

asexual reproduction

The creation of genetically identical offspring by a single parent, without the participation of sperm and egg.

sexual reproduction

The creation of genetically unique offspring by the fusion of two haploid sex cells (gametes), forming a diploid zygote.

binary fission

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

chromatin

The combination of DNA and proteins that constitutes eukaryotic chromosomes.

sister chromatids

Two identical parts of a duplicated chromosome in a eukaryotic cell. Prior to mitosis, these remain attached to each other at the centromere.

centromere

The region of a duplicated chromosome where two sister chromatids are joined and where spindle microtubules attach during mitosis and meiosis.

cell cycle

An ordered sequence of events that extends from the time a eukaryotic cell is first formed from a dividing parent cell until its own division into two cells.

interprhase

The period in the eukaryotic cell cycle when the cell is not actually dividing. It constitutes the majority of the time spent in the cell cycle.

mitotic phase (M phase)

The part of the cell cycle when the nucleus divides, its chromosomes are distributed to the daughter nuclei, and the cytoplasm divides, producing two other cells.

mitosis

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

cytokinesis

the division of the cytoplasm to form two seperate daughter cells. This division and mitosis make up the mitotic (M) phase of the cell cycle.

prophase

The first stage of mitosis, during which the chromatin condenses to form structures visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still intact.

prometaphase

The second stage of mitosis, during which the nuclear envelope fragments and the spindle microtubuls attach to the kinetochores of the sister chromatids.

metaphase

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.

anaphase

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 two poles of the cell.

telophase

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

mitotic spindle

A football-shaped structure formed of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis and meiosis.

centrosome

Material in the cytoplasm of a eukaryotic cell that gives rise to microtubules.

cleavage furrow

The first sign of cytokinesis during cell division in an animal cell, a shallow groove in the cell surface near the old metaphase plate.

cell plate

A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.

growth factor

a protein secreted by certain body cells that stimulates other cells to divide.

density-dependent inhibition

The ceasing of cell division that occurs when cells touch one another.

anchorage dependence

The requirement that to divide, a cell must be attached to a solid surface.

cell cycle control system

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

tumor

An abnormal mass of rapidly growing cells that forms within otherwise normal tissue.

benign tumor

An abnormal mass of cells that remains at its original site in the body.

malignant tumor

An abnormal tissue mass that can spread into neighboring tissue and to other parts of the body; a cancerous tumor.

metastasis

The spread of cancer cells beyond their original site.

carcinomas

Cancer that originates in the coverings of the body, such as skin or the lining of the intestinal tract.

sarcomas

Cancer of the supportive tissues, such as bone, cartilage, and muscle.

leukemias

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 calls that produce leukocytes.

lymphomas

Cancer of the tissues that form white blood cells.

somatic cell

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

homologous chromosomes

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 posses genes for the same characteristics at corresponding loci.

locus

The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.

sex chromosomes

A chromosome that determines whether an individual is male or female.

autosomes

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

life cycle

The entire sequence of stages in the life of an organism, from the adults of one generation to the adults of the next.

diploid

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

gametes

A sex cell; a haploid egg or sperm. The union of these two of oppsoite sex produces a zygote.

haploid

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

fertilization

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

zygote

The diploid fertilized egg, which results from union of a sperm cell nucleus and an egg cell nucleus.

meiosis

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

tetrads

A paired set of homologous chromosomes, each composed of two sister chromatids. These form during prophase I of meiosis, when crossing over may occur.

crossing over

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

chiasma

The microscopically visible site where crossing over has occurred between chromatids of homologous chromosomes during prophase I of meiosis.

genetic recombination

The producton, by crossing over and/or independent assortment of chromosomes during meiosis, of offspring with allele combinations different from those in the parents.

karyotypes

A display of micrographs of the metaphase chromosomes of a cell, arranged by size and centromere positionn. These may be used to identify certain chromosomal abnormalities.

trisomy 21

Down syndrome.

Down syndrome

A human genetic disorder resulting from the presence of an extra chromosome 21; characterized by hear and respiratory defects and varying degrees of mental retardation.

nondisjunction

An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.

deletion

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

duplication

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.

translocation

The attachment of a chromosomal fragment to a nonhomologous chromosome.