Mitosis is the cell division process that generates genetically identical daughter cells. All somatic cells and stem germ cells (spermatogonia/oogonia) proliferate by mitotic cell division.

Meiosis involves a two stage cell division (Meiosis I followed by Meiosis II). By means of meiosis, primary spermatocytes & oocytes generate haploid gametes (sperm & ova) that are unique regarding genotype.


GLOSSARY:
      chromatid: a copy of a chromosome. Following mitosis (prior to synthesis during interface), each chromosome consists of one chromatid. Following synthesis, each chromosome is composed of two chromatids linked by a centromere.

      chromatin: refers to stained chromosomes within the nucleus of a eukaryotic cell; inactive chromosomes stain distinctly (heterochromatin) but active chromosomes are uncoiled and do not stain distinctly (euchromatin).

      chromosome: double-stranded DNA and associated histone proteins located within the nucleus of a eukaryotic cell.

      homologous chromosomes: refers to genotypically similar chromosomes that constitute a paternal-maternal pair; the two are linked together during Meiosis I (predisposing to crossover exchange of genes).

      diploid (2N): refers to the typical number of chromosomes found in all body cells except secondary germ cells and gametes; chromosomes are present as homologous pairs in diploid cells.

      haploid (N): refers to the number of chromosomes found in secondary germ cells and gametes; individual chromosomes are represented by either the paternal or maternal chromosome per homologous pair.

      interphase: refers to the period in the cell cycle when synthesis occurs in preparation for mitosis or meiosis I; synthesis produces two chromatids per chromosome during interphase.

      meiosis: refers to germ cell divisions that give rise to four gametes that are haploid with unique genotypes (meiosis I produces haploid daughter cells and meiosis II generates unique gametes).

      mitosis: refers to the typical cell division that gives rise to two daughter cells, each have the same genotype as the parent cell.

Chromosomes are double strands of DNA and associated histone proteins, evident as stained chromatin within the nucleus of a eukaryotic cell. Chromosomes become distinct during cell division (mitosis/meiosis), when they become tightly coiled. Chromosomes are indistinct during interphase (because they are uncoiled while DNA is being transcribed or synthesized).


Following mitosis, at the start of interphase, each chromosome is composed of one chromatid (chromatin strand). Following DNA synthesis during interphase, each chromosome is composed of two chromatids connected by a centromere (required for mitosis).

Mitosis is the cell division process by which one parent cell produces two genetically identical daughter cells. Each daughter cell has a single chromatid per chromosome following mitosis. After DNA synthesis during interphase, each cell has two chromatids per chromosome and is prepared for mitosis.


The four stages of mitosis are:
      — prophase: chromosomes become visible and the nuclear membrane disappears
      — metaphase: double-chromatid chromosomes align along the nuclear equator
      — anaphase: chromatids separate and each chromatid is pulled toward a daughter cell nucleus
      — telophase: nuclear membranes reappear and chromosomes become indistinct as interphase ensues.

Meiosis is the cell division process by which one primary spermatocyte produces four spermatid gametes, each with a different genotype (also, one primary oocyte produces an ovum and three polar bodies).

Meiosis is a two stage process. In Meiosis I, the diploid primary germ cell divides into two secondary germ cells that are haploid. In Meiosis II, the haploid secondary germ cell (which has two chromatids per chromosome) divides into two haploid gametes each having one chromatid per chromosome.


The four stages of meiosis I are:
      — prophase: chromosomes become visible and the nuclear membrane disappears
      — metaphase: homologous pairs of double-chromatid chromosomes align along the nuclear equator; homologous chromosomes can exchange material (crossover)
      — anaphase: chromosomes per pair separate, one chromosome goes to each daughter cell (secondary germ cell)
      — telophase: nuclear membranes reappear (each secondary germ cell is haploid and genetically different) and meiosis II proceeds.


The four stages of meiosis II are similar to mitosis:
      — prophase: chromosomes become visible and the nuclear membrane disappears
      — metaphase: double-chromatid chromosomes align along the nuclear equator
      — anaphase: the two chromatids per chromosome separate, each chromatid moves to a daughter cell (gamete)
      — telophase: nuclear membranes reappear (spermatids morph into spermatozoa; one oocyte gets all of the cytoplasm.)

During gametogenesis, diploid (2N) germ cells produce haploid (N) gametes by meiosis. Via fertilization, gamete fusion produces a diploid zygote, the start of a new individual. Thus germ cells provide continuity between generations through transfer of chromosomal DNA.