Unit 5

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Unit 5: Cell Growth and
Reproduction
Unit 5: Cell Growth and Reproduction
• The events that occur during the cell cycle
– Interphase: The longest‐lasting phase of the cell
cycle in which a cell performs the majority of its
functions, such as preparing for nuclear division
and cytokinesis.
Unit 5: Cell Growth and Reproduction
• Nuclear division
– Mitosis: A nuclear division resulting in the
production of two somatic cells having the same
genetic complement as the original cell.
• Prophase: nucleus disappears, chromosomes pack
together.
• Metaphase: chromosomes line up in the center of the
cell.
• Anaphase: sister chromatids separate and move to
opposite sides.
• Telophase: chromosomes uncoil, both nuclei reform.
Unit 5: Cell Growth and Reproduction
• Nuclear division
– Meiosis: A two‐phase nuclear division that results
in the eventual production of gametes with half
the normal number of chromosomes.
• Meiosis I: homologous chromosomes separate.
– Prophase I: chromosomes pack tightly. Homologous
chromosomes pair up. Crossing over can occur.
– Anaphase I: homologous chromosomes separate and move to
opposite sides.
• Meiosis II: sister chromatids separate. There is no DNA
replication.
Unit 5: Cell Growth and Reproduction
• Nuclear division
– Cytokinesis: The final phase of a cell cycle
resulting in the division of the cytoplasm.
Unit 5: Cell Growth and Reproduction
• Compare the processes and outcomes of mitotic and
meiotic nuclear divisions
– Mitosis is used to repair cells, used in asexual reproduction, and
used in growth. Meiosis is only used for sexual reproduction.
– Mitosis produces genetically identical daughter cells. Meiosis
produces four different daughter cells with half the number of
chromosomes. Meiosis is only used to form gametes.
– How chromosome separation is different: the sister chromatids
do not separate in mitosis only the homologous chromosomes.
In meiosis I the homologous chromosomes separate. In meiosis
II then the sister chromatids.
– When the similar chromosomes line up early in meiosis, they
may swap portions. This is “crossing over” and makes the
product of meiosis (and sex) more varied and unpredictable.
Unit 5: Cell Growth and Reproduction
– Nondisjunction: The process in which sister
chromatids fail to separate during and after
mitosis or meiosis.
• If chromosomes or parts of chromosomes do not
separate correctly during any form of cell division, the
cells produced may have too much or too little genetic
information.
• If an egg or sperm has too many or too few
chromosomes, the entire organism formed from it will
usually not develop. Down syndrome (with an extra 21st
chromosome) is one of very few survivable situations.
Unit 5: Cell Growth and Reproduction
• How DNA replication results in transmission
and/or conservation of genetic information
– DNA replication: The process in which DNA makes a
duplicate copy of itself.
• Every time the cell divides, DNA must replicate. DNA copies
have to be accurate.
– Original strand of DNA used as a template. DNA is
built from 2 complementary strands. Every time more
DNA is copied, one of the “old” strands becomes
complement to the new. This maintains the correct
order of the code (usually).
– Base pairing rules: adenine with thymine. Cytosine
with guanine.
Video Review
• Mitosis Animation
• Mitosis Song
Video Review
• Meiosis Animation
• Meiosis Song
Video Review
• Mitosis vs. Meiosis
Video Review
• Nondisjunction
Video Review
• DNA Replication song
• DNA Replication Animation