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Cell Reproduction
Mitosis vs. Meiosis
Mitosis Exit Ticket Questions
Copy these questions in your notebook and answer before
the end of class. Show to Mrs. Millican before you leave. IT
IS A GRADE!!!
1. What is the purpose of mitosis? What kind of cells
does it occur in?
1. When is the DNA copied for the new cell?
1. How many chromosomes do human beings have?
1. Why aren’t chromosomes always visible?
How do little elephants grow up to be BIG
elephants?
Why do animals shed their
skin?
The process of asexual
reproduction begins after a
sperm fertilizes an egg.
Three reasons why cells reproduce
by asexual reproduction/mitosis:
1. Growth
2. Repair
3. Replacement
Skin cancer - the abnormal growth of
skin cells - most often develops on skin
exposed to the sun.
Cell that reproduce by asexual
reproduction reproduce constantly.
Eukaryotic Cell Division
Two forms
– Mitosis
• grow, replace dead or worn out cells, or to repair
wounds
• Asexual reproduction in fungi, protists, some
plants/animals
– Meiosis
• Sexual reproduction
Cell Division
• All cells arise from other cells by cell
division.
• When cells grow to a certain size they
must either divide or die.
• If a cell continued to grow without dividing,
the surface area of the cell would become
too small to hold the cell’s contents.
Cell Division
• Cell division is a complex series of changes in
the nucleus of a cell that leads to the production
of two new cells.
• The new cells are called daughter cells.
• The nuclei of the daughter cells are usually
identical to each other and to that of the parent
cell.
• The daughter cells grow and increase in size
until they divide and produce two more daughter
cells.
• This process continues, resulting in organism
growth and reproduction.
Mitosis
• All cells in the body (except sex cells) are
produced by the process of mitotic cell
division.
• Mitosis involves a complex series of
changes in the nuclei of body cells that
produce identical (same) daughter cells.
– They have the same number and type of
chromosomes as the parent cells.
The Cell Cycle – Stages of
Mitosis
Although the events of mitosis
are an ongoing process, they
are generally described in
terms of separate phases,
or stages.
– Interphase
– Prophase
– Metaphase
– Anaphase
– Telophase
Before Cell Division
Before mitosis can begin,
the cells chromosomes
must be duplicated. The
familiar X shape usually
shown in pictures of
chromosomes is actually
two chromosomes right
before mitosis or meiosis.
A Karyotype is an Arranged Picture of Chromosomes At Their Most
Condensed State
Note that almost all chromosomes come in homologous pairs.
A normal
human
karyotype
DNA is Condensed into Visible Chromosomes Only For Brief
Periods in the Life of a Cell
95% of the time, chromosomes
are like this.
Easily visible chromosomes are
apparent perhaps 5% of the time
in an actively growing cell and
less in a non-growing cell.
DNA is Packaged into Chromosomes
duplicated
chromosome
chromatin
The packaging is impressive – 2 meters of human DNA fit into a sphere
about 0.000005 meters in diameter.
Interphase
• Interphase is the period
between cell divisions.
• During interphase, the
single-stranded
chromosomes replicate
(make an extra copy).
• The chromosomes can
not be seen during
interphase.
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase
• In prophase, the doublestranded chromosomes
become visible, and the
nuclear membrane
disappears.
• A spindle apparatus,
consisting of fibers, forms
between opposite
poles of the cell.
Prophase
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
• During metaphase, the chromosomes move
toward the middle of the cell and line up at the
cell equator (midline).
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
• During anaphase, the double-stranded
chromosome separates and move to opposite
poles of the cell.
• There is a complete set of chromosomes at each
pole of the cell.
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase and
Cytoplasmic Division
• The last stage of mitosis is telophase.
• In telophase, a nuclear membrane forms around
each set of chromosomes, forming two identical
nuclei.
• At the end of mitosis,
the cytoplasm divides,
forming two new
identical daughter cells.
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
The Cell Cycle
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Meiosis
• The process of meiosis involves two cell
divisions and produces cells that are
different from the parent cell.
– Meiosis produces cells that have one-half the
number of chromosomes as the parent cells.
– If meiosis did not take place, the fertilized egg
would have double the amount of chromosomes
it needs.
• Meiosis produces the cells that are needed
for sexual reproduction (egg cells and sperm
cells).
Meiosis
• One-half the number of
chromosomes is called the
haploid, (or n) number.
– In humans, the haploid
number (n) is 23.
• When the egg and sperm
unite during fertilization, the
species normal
chromosome number
called the diploid or (2n)
number is restored
(brought back).
– The diploid number in
humans is 46.
– n (sperm) + n (egg) = 2n
Comparison of Mitosis and
Meiosis
Characteristic
Mitosis
Meiosis
Number of daughter cells
2
4
Number of cell division
1
2
Diploid
Haploid
Full set of chromosomes
Half the chromosomes
Identical
Different
Diploid
Diploid
Daughter cells are
diploid or haploid
Daughter cells are
identical or different
Parent cell is
diploid or haploid
Boy or Girl? The Y Chromosome “Decides”
DNA Structure
 DNA consists of two molecules that are
arranged into a ladder-like structure called a
Double Helix.
 A molecule of DNA is made up of millions of
tiny subunits called Nucleotides.
 There are four types of nitrogenous bases.
Nucleotides
A
Adenine
C
Cytosine
T
Thymine
G
Guanine
Nucleotides
 Each base will only bond with one other
specific base.
 Adenine (A)
 Thymine (T)
 Cytosine (C)
 Guanine (G)
Form a base pair.
Form a base pair.
A
T
C
G
T
A
C
G
A
T
G
C
T
A
DNA Structure
 To crack the genetic code found in DNA we
need to look at the sequence of bases.
 The bases are arranged in triplets called
codons.
AGG-CTC-AAG-TCC-TAG
TCC-GAG-TTC-AGG-ATC
DNA Structure
 A gene is a section of DNA that codes for a
protein.
 Each unique gene has a unique sequence of
bases.
 This unique sequence of bases will code for the
production of a unique protein.
 It is these proteins and combination of proteins
that give us a unique phenotype.
DNA
Gene
Protein
Trait

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