Friday 2-19-2010 Unit 6 Notes: Meiosis-2

(1) Meiosis 2 Events: DNA condenses. Sister Chromatids Line Up. Sister Chromatids separate. End up with 4, 1n cells!

(2) Genetic Information: Mitosis: Start 2n  “diploid” End 2n  “diploid” Meiosis: End 1n  “haploid”

(3) Meiosis-2 Stages: Prophase-2 Metaphase-2 Anaphase-2 Telophase-2 Cytokinesis  Not really part of Meiosis, but necessary!

(4) Prophase-2: Centrioles & Spindle Fibers prepare (again).

D d D d a A b B a A b B

(5) Metaphase-2: Sister Chromatids line up at the Metaphase Plate according to each other’s centromeres.

Sister Chromatids @ Metaphase Plate Centromere Cell Membranes A a a A D d d D b B B b Sister Chromatids @ Metaphase Plate

(6) Anaphase-2: Sister Chromatids separate. Law of Segregation: Alleles are separated so that each sperm/egg only has 1 allele/gene. Result = A sperm/egg with ½ the DNA Independent Assortment: Alleles are separated completely randomly. Alleles separate w/o regard to other genes.

Randomly & Independently Separated Chromosomes Cell Membranes a A a A d D d D b B B b Randomly & Independently Separated Chromosomes

(7) Telophase-2: Chromosomes unwind back to regular DNA. Nucleus reforms around DNA.

Reforming Nucleus d B D b a A b b B D d Cell Membrane a A

(8) Cytokinesis: Cytoplasm pinches off. Cell membrane closes around each of the 4 daughter cells.

Haploid Daughter Cells B D a A b Haploid Daughter Cells B b d A D a