Mitosis • cell division for growth, healing & asexual repro. 1

diploid set 2 identical diploid sets somatic cells• Interphase: replication = 90% of cycle so…chromatin • then Mitosis: P M A T 1. Prophase: chromatin condenses visible chromosomes

homologous pairs vs dupl. chromosomes membrane breaks & centrioles move to poles

Early prophase Late prophase

more Mitosis2. Metaphase: replicated chromosomes line up at equator end-to-end spindle fibers attach to chromatids = decision made notice # of fibers one per chromatid what is going to get separated from what?so what is a spindle fiber? Elastic connective tissue …and what if it gets old and loses its elasticity?

Transition to metaphase Metaphase

and more still3. Anaphase:

centromere breaks down = chromatids not held together fibers retract to separate chromatids

what is being separated here?what is staying together (NOT

separated)? …and remember what happens when those fibers get old and lose their elasticity?

…last one4. Telophase: centrioles back to original position

nuclear membrane forms x 2 THEN…..

Cytokinesis: cleavage furrow

…..and we start over again

Telophase Cytokinesis

Diagrammatic representations for the major stages of prophase I of meiosis I (above) and photographs of such stages (below)

Interphase L Zygotene P Diplotene Diakinesis

Metaphase I Anaphase I Telophase I INT Prophase II

Diagrammatic representations for the major stages of meiosis I (above) and photographs of such stages (below)

Diagrammatic representations for the major stages of meiosis II (above) and photographs of such stages (below

Metaphase II Anaphase II Telophase II Tetrad stage

Diagrammatic illustration of chromosome types, based on centromere position as defined by Levan et al., 1964

Karyotype preparation based on chromosome length and centromere position

Metacentric Submetacentric Acrocentric Telocentric

• What is crossing over? How does it work?

• The result? Swapped alleles between homologous pairs Would swapping alleles between chromatids in

a dupl. chromosome change anything?

So, vs Mitosis: 1. Prophase is longer 2. Side-by-side 3. Crossing over

• Metaphase 1: Chromosomes already lined up so all that’s left to do is... Spindle fibers attach notice # of fibers (vs Mitosis) one / dupl. chromosome what is going to get separated from what?

The decision is made = “Independent Assortment” decision made independently at each chromosome

Metaphase - mitosis

XX XX XX XX

Metaphase 1 of meiosis

So, vs mitosis: Metaphase is shorter

vs

• Anaphase & telophase similar to Mitosis• Second round of cell division separates chromatids one from

another – just like Mitosis

1st round 2nd round