Mitosis

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 Mitosis
2. 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 still
3. 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 one
4. 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

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

Metaphase I Anaphase I Telophase I INT Prophase II

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 1 of So, vs mitosis:
meiosis Metaphase is shorter

vs XX XX XX XX

Metaphase - mitosis

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

1st round 2nd round

Mitosis

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Mitosis