Cell reproduction
 Cancer cells
o Cancer cells differ from normal cells for the following reasons:
 Uncontrolled growth
 No contact inhibition
 Disorganized and multilayered
 Not specialized
 Abnormal nuclei
 Do not undergo apoptosis
 Crossing over v. mutation
o Crossing over occurs when 2 homologous chromosomes swap genetic
information. The exchange is for equal information, and just leads to
more variety.
o Mutations occur when there are changes to the DNA code (a gene
mutation), or errors on a particular chromosome (deletion – section
missing, duplication – section repeated, inversion – section flipped
backwards, and translocation – two non-homologous chromosomes
swap information)
 Mitosis v. meiosis – steps/phases
o Interphase is not part of either
o Mitosis
 Prophase – chromosomes become visible, spindle fibers form,
nuclear membrane and nucleolus disappear, centrioles move to
opposite poles
 Metaphase – chromosomes line up along the metaphase plate
 Anaphase – sister chromatids separate, becoming daughter
chromosomes
 Telophase – cytokinesis is completed; cleavage furrow or cell
plate forms, spindle fibers disappear, nuclear membrane and
nucleolus reappear, chromosomes turn back into chromatin
o Meiosis
 Prophase I – Same as in mitosis, except homologous
chromosomes will pair up, and crossing over may occur
 Metaphase I – Homologous chromosomes line up in pairs at the
metaphase plate
 Anaphase I – Homologous chromosomes separate
 Telophase I – Same as telophase in mitosis, except the cell is now
haploid
 Prophase II – Same as prophase in mitosis, except the cell is
haploid
 Metaphase II – Same as metaphase in mitosis, except the cell is
haploid
 Anaphase II – Same as in anaphase, except the cell is haploid
 Telophase II – Same as in telophase, except the cell is haploid
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G1, S, G2 stages?
o These are collectively called interphase; the period in between cell
divisions
o G1 – cell growth, making proteins
o S – DNA replication occurs
o G2 – Cell prepares for cell division
When would mitosis occur? Get a cut? Growing? Both?
o Mitosis would occur for any of these reasons: growth, repair of an
injury (cut, broken bone, etc.), fighting infection, and replacing worn out
cells
Crossing over
o This can occur during prophase I of meiosis, when homologous
chromosomes wrap so tightly around each other that they swap
information. The exchange is equal, and just results in more variety
Gametes and zygotes
o Gametes are haploid sex cells (cells that have half the number of
chromosomes as the body cells), such as an egg cell in a female, and a
sperm cell in a male
o Zygote is the fertilized egg that forms when a sperm cell fuses with an
egg cell
Meiosis I v. II – how to tell which phase is which in diagram
o You need to know either the diploid or haploid number of chromosomes
for that cell. If you know one, you can figure out the other.
 Diploid/2n
 Haploid/n
 If diploid number = 8, then haploid number = 4
o If cell being created has the haploid number of chromosomes, you know
you are looking at a cell in meiosis, and it must be in telophase I or later.
o If the cell has 2 sister chromatids still attached, and is forming a
cleavage furrow, it is in telophase I rather than telophase II, in which
you would see chromosomes with only 1 chromatid while the cell is
forming a cleavage furrow
o If you see a cell with the haploid number of chromosomes and no
pairing of homologous chromosomes, you know you are looking at a cell
in meiosis II
o If you see a cell with the diploid number of chromosomes, you are either
looking at a cell in mitosis, or a cell in prophase I or metaphase I of
meiosis.
o If the chromosomes are pairing up, it must be either prophase I (paired,
but not lined up), or metaphase I (lined up in pairs in the middle of the
cell)