Mitosis and Meiosis

Mitosis

• Begins with a cell that has a diploid number of chromosomes (2n).
• In humans, this is 46 chromosomes comprised of 23 from each parent forming 23 homologous pairs.
• After mitosis and cytokinesis, two cells with the same genetic information as the original are produced.
• Each new cell has a diploid number of chromosomes (2n).
• The new cells can undergo interphase again to grow, replicate DNA and centrosomes.
• Mitosis is facilitates growth, transforming single-celled organisms into complex beings.
• A cycle which each cell can repeat.

Meiosis

• Involves two phases, beginning with a cell that has a diploid number of chromosomes,
• DNA is replicated during interphase.
• Meiosis One halves the chromosome number, resulting in two cells with a haploid number of chromosomes (n).
• In humans, chromosome numbers reduce from 46 to 23 in each nucleus.
• Each of these cells then undergoes Meiosis Two, yielding four cells that each have the haploid number of chromosomes
• The four cells don't all necessarily have the same genetic information anymore.
• During Meiosis One, homologous pairs split up randomly, resulting in cells with chromosomes from both parents.
• Meiosis Two is similar to mitosis, dealing with cells that start with the haploid number.
• Meiosis is not a cycle; the resulting cells are gametes (sex cells).
• In males (testes), these are sperm cells; in females (ovaries), they are egg cells.
• In trees, these could be pollen or an ovule and these are used for fertilization.
• During sexual reproduction, gametes fuse to form a fertilized egg that undergoes mitosis to create a new organism.

Cell Types

• Mitosis occurs in somatic cells, which make up the bulk of the body.
• Meiosis occurs in germ cells (testes in males, ovaries in females).

Germ Cells

• Germ cells can undergo mitosis to produce other germ cells with a diploid number of chromosomes.
• Alternatively, germ cells can undergo meiosis to produce gametes (sperm or egg cells).