9th Grade Cellular reproduction

Chromosomes are condensed DNA.

• The Centromere is part of chromosome where sister chromatids are held together.

• 1chromosome = 2 chromatids 

  </p>

MITOSIS (ASEXUAL REPRODUCTION)

• Mitosis’s function is to grow and repair/maintain body.
  • A cell grows, and divides, and repeats during its life.
• 1 parent cell (46 chromosomes) produces 2 identical daughter cells (46 chromosomes each). 
• Your cells do not divide (perform mitosis) continually. Most of the time, they are in interphase.
• Cancer is when cells uncontrollably divide. 

\
INTERPHASE (PRE MITOSIS)

• The cell grows in size and performs regular functions.
• Chromosomes are replicated (doubled).

\
FOUR STAGES OF MITOSIS

• PMAT : Prophase, Metaphase, Anaphase, Telophase
• Prophase 
  • Centrioles (poles) appear and move to opposite ends of cell.
  • Spindle fibers form between the poles.
• Metaphase
  • Chromatids line up in the middle of the cell and attach to the spindle fibers.
• Anaphase
  • Chromatids separate and begin to move to opposite ends of of the cell.
• Telophase
  • Two new nuclei form and the chromosomes appear as chromatin (threads rather than rods).
  • Mitosis ends.

\
Cytokinesis 

• Cell membrane moves inward to create two daughter cells (each with its own nucleus and identical chromosomes). 

\
\
MEIOSIS (SEXUAL REPRODUCTION) 

• Prophase 1

  • Chromosomes line up with their homologous pairs. 
  • Homologous chromosomes are 2 chromosomes that are about the same size & have the same gene type in the same place.
  • Crossing over occurs (homologous pairs transfer their genetic info, creating recombinant chromosomes).

• Metaphase 1 

  • Chromosomes line up in the middle of the cell in pairs and attach to spindle fibers.

• Anaphase 1

  • The spindle fibers pull the homologous chromosomes apart and they move to opposite ends of the cell.

• Telophase 1 and Cytokinesis (ends meiosis one)

  • The nuclear membranes reform around the chromosomes, the two cells are separate.

• Prophase 2

  • The two haploid cells start to go through meiosis 2.
  • The cells nuclear membrane breaks back down, and spindle fibers begin to form. 

• Metaphase 2

  • Chromosomes line up in the middle of the cell and attach to spindle fibers (single file).

• Anaphase 2 

  • Sister chromatids separate and are pulled to opposite sides of the cell by spindle fibers.

• Telophase 2 and Cytokinesis

  • The nuclear membranes reforms.
  • Four new haploid cells (23 chromosomes) have formed!
  • These cells are gametes, and each one is unique and different from each other (NO identical cells, unlike cells from mitosis). 

• Nondisjunction occurs when chromosomes don't separate correctly.

  • A cell may receive too many or too little chromosomes in the separation. 

  \n \n \n \n \n \n