Only $2.99/month

Terms in this set (37)

Mitosis is cell division that preserves the original parental number of chromosomes in the 2 daughter cells.

Functions of mitotic cell division:
1. Asexual reproduction: unicellular protists like amoeba example budding of unicellular fungi like yeast.
2. Development - cleavage
3. Tissue growth and repair.

PROPHASE - Centrosomes move to opposite poles. Spindle microtubules and asters begin to form. Replicated chromosomes begin to condense.

PROMETAPHASE - Nuclear membrane breaks down because sister chromatids will need to separate into two daughter cells.
A kinetochore (kt) protein-complex appears at each centromere and attaches the centromeres of sister chromatids to spindle fibers.
The spindle is now complete.
Non-kt microtubules go pole to pole.
Kt molecules go pole to kt.
Aster microtubules "anchor" the centrosome to cell membrane.

METAPHASE - Spindle microtubules moves the chromosomes. Chromosomes line up along the midline/metaphase plate/equator.
Note++ The two sister chromatids of replicated chromosome face opposite poles

ANAPHASE - Centromeres split. Spindle microtubules shorten and pull apart sister chromatids toward opposite poles. Once separated each sister chromatid is now called a chromosome.
Note spindle microtubules shorten at the the kinetochore and pull chromosomes toward pole of the cell breaking the centromere apart.

TELOPHASE - Spindle disassembles. Nuclear membrane reforms. Mitosis = nuclear division.
Nuclear division is now complete.

CYTOKINESIS - Last part of the M phase. Cell membrane pinches together at the cleavage furrow. Cytoplasm division is now complete. Cell division is now complete.
Result: 2 daughter cells. Each has the same number of chromosomes as the parent cell and each has identical DNA sequence as the parent cell.

Meiotic cell division: a diploid cell divides to form 4 haploid daughter cells. Requires two cell divisions and reduces the diploid chromosome number in half. A REDUCTION DIVISION - REDUCES THE CELL FROM 2N TO N.

PROPHASE 1 - SYNAPSIS, homologous chromosomes pair up and form tetrads
CROSSING OVER - non-sister chromatids in a tetrad exchange equivalent segments at a CHIASMA.
Centrosomes move to opposite poles. Spindle microtubules and asters begin to form. Replicated chromosomes begin to condense.

METAPHASE I - TETRADS line up at the metaphase plate. PAIR not individual chromosomes. Therefore. A diploid number of 6 in G1 yields 12 chromosomes after S which form 3 tetrads, 6 homologous chromosomes.
Meaning that at metaphase 1 there is still only 6 chromosomes.

ANAPHASE I - Separation of homologous chromosomes. The tetrads are broken up! Still two chromosomes in each pair.

TELOPHASE 1 AND CYTOKINESIS - Ends with 2 haploid cells but sister chromatids are still attached. Each cell has three homologous pairs, therefore each has three chromosomes. DO NOT UNDERGO INTERPHASE. A nuclear envelope reforms around each chromosome set, the spindle disappears, and cytokinesis follows. In animal cells, cytokinesis involves the formation of a cleavage furrow, resulting in the pinching of the cell into two cells. After cytokinesis, each of the two progeny cells has a nucleus with a haploid set of replicated chromosomes.

PROPHASE II - Centrosomes move to opposite poles. Spindle microtubules and asters begin to form. chromosomes begin to condense.

METAPHASE II - Attached sister chromatids line up at the midline. Note orientation to the poles.

ANAPHASE II - Sister chromatids separate

TELOPHASE II AND CYTOKINESIS - Nuclear envelope reforms, cleavage occurs. 4 haploid daughter cells.