Bio Vocab 8B

Anaphase

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 the two poles of the cell.

Autosome

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

Chiasma

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

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.

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 genetic disorder caused when abnormal cell division results in extra genetic material from chromosome 21. Also called trisomy 21.

Fertilization

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

Gametes

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

Genetic Recombination

The exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent.

Haploid Cell

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

Homologous Chromoomes

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 characters at corresponding loci.

Interphase

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

Karyotype

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

Locus

The particular site where a gene is found on a chromosome.

Meiosis

In a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter nuclei.

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.

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.

Prophase

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.

Sex chromosome

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

Somatic cell

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

Telophase

The fifth and final stage of mitosis, during which daughter nuclei form at the two poles of a cell.

Tetrad

The foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

Trisomy 21

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.

Zygote

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