Biology 26

crossing over

A condition where non-sister chromatid of homologous chromosomes exchange genes.

chromatid

A double-stranded chromosome following replication attached by a centromere.

spindle fibers

A number of threadlike filaments formed between poles of the cell during cell division to which the centromeres of chromosomes attach; used to pull chromosomes apart and segregate them during anaphase.

centromere

A structure on the chromosome that holds a pair of chromatids together during replication.

tetrad

During metaphase I the two pairs of chromatids of the homologous pair of chromosomes comes together; crossing-over can occur at this time.

polar body

One of three small cells produced during oogenesis, each contain the haploid number of chromosomes.

oogenesis

Process of development of haploid female gametes.

spermatogenesis

The production of haploid male gametes by the male parent.

Prophase I

The stage in the first meiotic division where the doubled chromosomes become visible and nuclear membrane disappears.

Metaphase I

The stage in the first meiotic division where the homologous chromosomes line up as a pair, forming a tetrad of chromatids, at the equator of the cell.

Anaphase II

The stage in the second meiotic division where sister chromatids of a chromosome split and migrate to opposite poles.

Metaphase II

The stage in the second meiotic division where the chromatid pair lines up at the equator of the cell..

Telophase I

The stage of the first meiotic division where the cell divides into two cells each containing one member of each pair of homologous chromosomes.

Telophase II

The stage of the second meiotic division when the cell divides into two cells with each being haploid; these cells become the gametes.

Anaphase I

The stage on the first meiotic division when the homologous chromosomes move to opposite poles but the sister chromatids remain together.