Chapter 14 Meiosis Terminology

Gamete

A haploid sex cell (sperm or egg) formed through meiosis; fuses during fertilization to form a zygote.

Haploid

Having a single set of chromosomes (n); characteristic of gametes.

Diploid

Having two complete sets of chromosomes, one from each parent (2n); characteristic of somatic cells.

Somatic Cell

Any cell of a living organism that is not a germ cell; these diploid cells make up the body's tissues and organs.

Germ Cell

A cell that is destined to become a gamete (sperm or egg); undergoes meiosis.

Meiosis

A two-stage type of cell division that produces four genetically unique haploid gametes from one diploid cell.

2n

Symbol representing the diploid number of chromosomes.

n

Symbol representing the haploid number of chromosomes.

Autosome

Any chromosome that is not a sex chromosome; humans have 22 pairs of autosomes.

Tetrad

The paired and aligned structure formed by two homologous chromosomes, each composed of two sister chromatids, during Prophase I of meiosis.

Chiasma

The physical point of contact where crossing over occurs between non-sister chromatids of homologous chromosomes.

Prophase I

The first phase of meiosis I; chromosomes condense, homologous chromosomes pair up to form tetrads, and crossing over occurs.

Metaphase I

The phase of meiosis I where tetrads align at the metaphase plate and independent assortment occurs.

Anaphase I

The phase of meiosis I where homologous chromosomes are pulled apart and move to opposite poles of the cell.

Telophase I

The phase of meiosis I where chromosomes arrive at opposite poles, the cell divides, and two haploid cells are formed.

Prophase II

The first phase of meiosis II; the nuclear envelope breaks down and chromosomes condense in the two haploid cells.

Metaphase II

The phase of meiosis II where chromosomes line up single file at the metaphase plate in each haploid cell.

Anaphase II

The phase of meiosis II where sister chromatids are pulled apart and move to opposite poles.

Telophase II

The final phase of meiosis II where nuclear membranes reform, and the cells divide to yield four haploid gametes.

Independent assortment

The random orientation of homologous chromosome pairs during Metaphase I, leading to gametes with random combinations of maternal and paternal chromosomes.

Fertilization

The fusion of two haploid gametes (sperm and egg) to form a diploid zygote.

Zygote

The diploid cell formed by the fusion of two gametes; the first cell of a new organism.

Crossing over

The process in Prophase I where non-sister chromatids of homologous chromosomes exchange segments of DNA.

Recombination

The general process that results in new combinations of genetic material; crossing over is a specific example.

Nonsister chromatid

A chromatid from one member of a homologous chromosome pair, paired with a chromatid from the other chromosome.

Sexual reproduction

A type of reproduction involving the fusion of gametes, leading to genetically diverse offspring.

Asexual reproduction

A type of reproduction involving a single parent, producing genetically identical offspring (clones).