Download Haploid: A cell containing a single set (n) of chromosomes. May be

MITOSIS AND MEIOSIS: SOME DEFINITIONS
Haploid: A cell containing a single set (n) of chromosomes. May be the natural state of the
organism or a gamete of a diploid organism.
Diploid: A cell containing two sets (2n) of chromosomes (one from each parent).
Chromatids: Identical daughter chromosomes resulting after duplication and are joined at
the centromere (also called sister chromatids).
Homologous chromosomes: Chromosomes that code for the same genes but come from
different parents (also called non-sister chromatids).
Crossing over: Occurs in Meiosis I. Involves swapping of DNA fragments between
homologous chromosomes. Produces chromosomes with different allelic complements.
Mitosis: Needed for growth, repair, and development in multicellular organisms. Yields two
daughter cells that are identical (barring mutation) to the parental cell in allelic
complement and chromosome number, n. Referred to as a mechanism of constancy.
- Sequence – Figure 12.5 page #218.
Meiosis: Needed for gamete cell formation in sexual organisms. Involves two rounds of cell
division, Meiosis I (reduction division) and Meiosis II (analogous to Mitosis). Yields cells
that have half the number of chromosomes and different gene combinations (because of
crossing over) when compared to parental cell. Referred to as a mechanism of diversity.
- Sequence – Figure 13.7 page #240.
Table 1: A brief comparison of mitosis and meiosis.
Interphase (I)
Prophase (I)
Metaphase (I)
Anaphase (I)
Telophase (I)
Cytokinesis
Prophase (II)
Metaphase (II)
Anaphase (II)
Telophase (II)
Cytokinesis
-
Meiosis
chromosomes, centrosomes duplicate
chromosomes condense
centrosomes - opposite ends of cell
homologous chromosomes pair
- form tetrads
nuclear membrane disappears
crossing over occurs
tetrads line up at equator
homologous chromosomes pulled apart
nuclear membranes appear
two haploid (n) cells are formed
- chromosomes are still doubled
no replication is required
chromosomes condense
centrosomes - opposite ends of cell
nuclear membranes in both cells disappear
chromosomes line up at equator
chromatids pulled apart
nuclear membranes appear
four haploid (n) cells are formed
each is different if crossing over occurs
- two pairs of identical cells If not
- meiosis is complete
-
-
Mitosis
chromosomes, centrosomes duplicate
chromosomes condense
centrosomes - opposite ends of cell
nuclear membrane disappears
chromosomes line up at equator
chromatids pulled apart
nuclear membranes appear
two diploid (2n) cells are formed
- identical to parent cell
- mitosis is complete