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Mitosis and Meiosis. Chromosomes made of DNA wrapped around histone protein (beads) to make nucleosomes. Chromatin - mixture of DNA and protein that makes up chromosome Chromosomes make possible the precise separation of DNA during cell division. Chromosome parts Telomere - end

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Chromatin - mixture of DNA and protein that makes up chromosome

  • Chromosomes make possible the precise separation of DNA during cell division

Chromosome parts

Telomere - end

Centromere - middle

Arms - chromatids


Interphase (‘in between’)

  • 1) cell grows (G1)
  • 2) DNA duplicates (S)
  • 3) Cell produces organelles for division (G2)

Basically, the cell is growing and getting ready for division


Before chromosome duplication (replication)

  • Called diploid (2N) because you have one chromosome from each parent

Mitosis - cell division starts in the nucleus

  • Stages:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

3) Anaphase - sister chromatids separate and move toward centrioles (where spindles originate)


Cytokinesis - final splitting of one cell into two

Animal cells - cell membrane is pinched inward


Plant cell cytokinesis- membrane too rigid to move due to cell wall - so a plate forms halfway between 2 new nuclei

  • Cell division to produce gametes (sex cells)

Ploidy - number of sets a chromosome in a cell nucleus

  • Notice these chromosomes

are not duplicated


Meiosis - can be broken into Meiosis I and Meiosis II

  • Before Meiosis I, chromosomes replicate
  • Before Meiosis II, chromosomes do not replicate

Meiosis I (steps)

  • 1) Chromosomes duplicate (interphase)

Step 2) Prophase I- paired homologous chromosomes form tetrads

  • Crossing over -

homologous chromosomes

exchange alleles!

Crossing over creates new

Combinations of alleles

In daughter cell

(shuffles genetics)


Step 3) Metaphase I - paired homologous chromosomes line up in center of the cell and are pulled apart

meiosis i vs mitosis
Meiosis I vs. Mitosis
  • Daughter cells in meiosis I do not have identical chromosomes as parent cell
  • 2 daughters are haploid because during division, each daughter gets one half of the homologous pair
  • Crossing over makes it so each daughter cell doesn’t just have chromosome from one parent
meiosis ii
Meiosis II
  • Difference: chromosomes do not replicate before this division
meiosis ii1
Meiosis II
  • In meiosis II, the two

daughter cells from

meiosis I split back

into separate


(go haploid)


Meiosis II produces 4 haploid gametes. (sperm, egg) These cells are incomplete and need to be paired with an opposite gamete to have full genetic information.