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1/25/2013
1
Today:
Presentations! Topic
Due Thursday!
Looking at Cell Division- Mitosis! (In-
Class 4)
Preview of Meiosis?
Why do cells do Mitosis?
1. Growth &
Development
2. Repair
What’s important about Mitosis?
Mitosis (cell division) must be very precise for
both DNA replication (more later) and parceling out the
DNA to the new cells!
Abnormal division triggers cancer…
Bladder cancer cells.
(Photo by Nancy Kedersha)
Words to Know: GENOME: the collection of all a cell’s genetic information
CHROMOSOMES: The packaging unit for DNA.
Each species has a characteristic number of chromosomes. (Humans = 46, except in sex cells) Chromosomes are composed of
CHROMATIN.
SISTER CHROMATIDS: As a chromosome is
duplicated, it forms a set of two sister chromatids. The chromatids have a narrow “waist” called the CENTROMERE.
A single
CHROMOSOME
duplicates to form a pair of
SISTER
CHROMATIDS, with a visible
CENTROMERE.
Homologous Chromosomes
DIPLOID organisms (like
us) have two of each chromosome
(one from each
parent). These pairs are called
HOMOLOGOUS Chromosomes.
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The Mitotic Cell Cycle: An Overview
~90% of the cell cycle
Mitosis Occurs in 4 Steps:
Prophase Metaphase Anaphase Telophase
Step 1: Prophase
Chromatin (DNA) condenses to form
‘visible’ chromosomes
Microtubules are reassembled, spindle begins to form
Nuclear envelope breaks up
Step 2: Metaphase
Spindle is complete
“Push-pull” aligns chromosomes at
the midpoint to form the
METAPHASE PLATE
Step 3: Anaphase
Sister Chromatids separate and
migrate towards opposite spindle
poles
Step 4: Telophase
Chromosomes arrive at poles and
relax
Nuclear membrane reforms
Spindle is disassembled
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CYTOKINESIS Let’s Watch!
Check out these cancer cells: http://www.microscopyu.com/moviegallery/livecellimaging/a549/index.html
Or Mitosis in a Pig Kidney Cell:
http://www.microscopyu.com/moviegallery/c1si/mitosiseb3/index.html
Last but not least, Lung of Newt! http://video.google.com/videoplay?docid=-990474875075679903&ei=7cDgSsKCNZWUqAPP-
f3CDA&q=mitosis+in+newt+lung&hl=en#
Modeling Mitosis
With a neighbor or two, build some chromosomes! If you are building sister chromatids, make them the same color and length.
If building homologous chromosomes, make them
different colors but the same length. With your group, walk
through each stage, making sure you can explain what’s
happening at each!
Fill-in Part 1, AC
Asexual vs Sexual Reproduction
Advantages and Disadvantages?
Asexual
Reproduction occurs
through MITOSIS and
CYTOKINESIS
The resulting
offspring are
CLONES! (genetically
identical to the
parent)
Sexual Reproduction Genetic
Variation!
Through sexual reproduction, offspring inherit
new combinations of alleles.
An ALLELE is a “version” of a particular gene
Genetic Diversity is
Essential for Evolution!
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Sexual
Recombination
Requires
Haploid
Gametes
A Graphical
Overview of Meiosis
Meiosis occurs in two stages:
Meiosis I- Homologous chromosomes separate
Meiosis II- Sister
chromatids separate
Meiosis II Meiosis II
You Try: 2AC
Meiosis Creates Genetic
Diversity:
Crossover
Homologous
Chromosomes are
INDEPENDENTLY (randomly)
parceled out during
Meiosis I
Meiosis Creates Genetic Diversity: Random Fertilization
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8 million possible
chromosome
combinations in each egg, and each sperm…
= >70 trillion possibilities!
Meiosis Creates Genetic Diversity: Random Fertilization
Meiosis: What can go wrong??
You Try: 2D
Nondisjunction can result in an abnormal chromosome number
Red viscacha rat from Argentina = 4n
XXY = Klinefelter Syndrome-
male with normal
intelligence, sterile
XO = Turner syndrome-
phenotypically female, sterile, usually normal
intelligence
XYY = no general traits (tall)
XXX = healthy, “normal”
Nondisjunction can result in an abnormal chromosome number
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