Bio 006 - 10LB: Meiosis*

Mitosis

Process producing 2 identical diploid daughter cells.

Stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase / Cytokinesis

Meiosis

Process producing 4 non-identical haploid gametes from 1 diploid cell.

• Goes through the stages of Mitosis TWICE

Interphase

Phase where cell prepares for division.

G1 Phase

First interphase stage (focuses on Growth)

• Cell grows bigger

• Copies some organelles

• Makes building blocks for chromosomes to form

• Build centromeres

• Saving up energy for replication

S Phase

DNA synthesis; duplication of centromeres occurs.

• Necessary for us to have 2 copies

• 2 sister chromatids

• These chromatids attach to centromeres

• Also duplicates centrosomes (important in mitosis AND MEIOSIS)

G2 Phase

Final interphase stage before mitosis

• Store more energy

• Copies some organelles

• Make proteins for chromosome manipulation (i.e. during mitosis)

• Cytoskeleton gets dismantled (taken apart).

Prophase 1

• Chromatin condenses to form chromosomes

• nuclear envelope breaks down

• Centrosomes start moving to poles

Metaphase I

Chromosomes align at the metaphase plate in tetrads in Meiosis. This is where independent assortment takes place

Anaphase 1

Chromatids pulled to opposite poles by spindle fibers.

• from Mitosis: sister chromatids

• from Meiosis: recombined homologous chromosomes

Telophase 1

Nuclei form at poles; cell prepares to divide.

Result: 2 non-identical haploid cells

• Now, each of these cells will divide again in M2.

Cytokinesis

Division of cytoplasm following mitosis or meiosis.

Tetrad

Set of 4 chromatids formed during meiosis in Prophase 1.

Synapsis

Homologous chromosomes pairing during Prophase I.

Crossing Over

Genetic recombination between homologous chromosomes in Prophase 1.

Independent Assortment

Random distribution of alleles during gamete formation in Metaphase 1 during Meiosis

Diploid

Cell with two sets of chromosomes (2n).

Haploid

Cell with one set of chromosomes (n).

Centromere

Region where sister chromatids are joined.

Kinetochore

Protein structure where spindle fibers attach.

Spindle Fibers

Microtubules that pull chromosomes apart.

Gametes

Reproductive cells formed through meiosis.

Zygote

Fertilized egg formed from gametes.

Lab Practical

Hands-on assessment of knowledge and skills.

PMAT

Abbreviation of the 4 Stages in Mitosis/Meiosis

Prophase 2

• Nuclear envelope breaks down (again)

• New spindle fibers form

• Centrosomes move to poles

Metaphase 2

• Chromosomes line up at metaphase plate

• Spindle fibers from centrioles attach at kinetochore

• Chromosomes single file, same as in mitosis (except now, recombined)

Anaphase 2

Spindle fibers pull sister chromatids to opposite poles

• Similar to mitosis

Telophase 2

• Distinct nuclei (i.e. new nucleuses) form at opposite poles

• Cell ready to divide

• At the end we have: 4 haploid non-identical cells (gametes)