What is mitosis?
-Process in which a cell divides, creating TWO complete
Sets of the original cell with the same EXACT genetic
Material (DNA)
Cell Division
Produces CLONES with the same # of
chromosomes and same EXACT chromosomes
-DNA
Replicates
(Copies itself)
-copied DNA
Pairs up
-Nuclear membrane
Disappears
-Paired chromosomes
Meet in the middle
-chromosomes
Are pulled
apart
-Mitosis is
rapid cell division
and produces
large #’s of
offspring
Ex: Skin Cell
(Body Cell)
Is mitosis
Asexual or
Sexual
Reproduction?
-Two complete
Cells formed
Identical to original
-cytoplasm pinches
in
-nuclear membrane
reappears
-Asexual
What is cancer?
-Uncontrollable cell division
Cancer is rapid MITOTIC
cell division
How can I remember the stages of mitosis?
P= pair up
M= meet
A= apart
T= two
Chromosome- Coiled strands of genetic material (DNA)
found inside the nucleus of eukaryotic cells
Haploid- Cell that contains ½ the normal number of
chromosomes (n)
Ex: Human Cell=23, Potato Cell= 24
Diploid- Cell that contains the full number of
chromosomes (2n)
Ex: Human cell = 46, potato cell= 48
Chromatin- Long strands of DNA found in the nucleus
Homologous Chromosomes-A pair of chromosomes that
are the same length and have
the same inherited characteristics
How many chromosomes are found in each of the following?
Diploid (2n)
Human Cell= 46 (23 pairs)
Gamete= Sex Cell= 23 (1/2 normal cell!!)
Haploid (n)
Zygote= Fertilized egg= 46 (23 pairs)
Sperm + Egg (n+n=2n)
=
+
(1/2 DNA)
(1/2 DNA)
1 whole
Where do sex cells come from, since they only have
½ the normal number of chromosomes?
Meiosis- Cell division that creates
gametes (sex cells)
Meiosis converts a diploid cell into a haploid cell
“In-between phase”
Interphase- All cells remain in this
phase when they are NOT dividing
**Right before entering prophase DNA replicates (copies)
Prophase I- “P”
-copied DNA pairs up into HOMOLOGOUS PAIRS
(find their “match” = little “X’s”)
-Nuclear membrane disappears
-Spindle forms
Metaphase I - “M”
-Homologous Pairs “meet” in the middle
Anaphase I-”A”
-Homologous pairs split apart (each side contains
Same # of chromosomes as parent cell)
-Cell begins to “pinch” in (cytokenesis)
Telophase I-”T”
-2 new cells created with the SAME
# of chromosomes as the original cell
(Cytokenesis complete; Cell splits)
-Nuclear membrane comes back in BOTH cells
Meoisis I produces the same end product as
(2 Identical Cells with the
normal chromosome # )
If meiosis produces gametes (1/2 original chromosome #),
what happens next???
- A second division MUST occur
Meiosis II starts out with 2 cells with Double-Stranded chromosomes
It ends with 4 cells with Single-Stranded chromosomes
Prophase II-
-same as Prophase I
occurring in BOTH cells
**There is no replication of DNA in Meiosis II
-Cells go from Telophase I into Prophase II
Anaphase II-
Metaphase II-
Telophase II
At the end of Telophase II:
Males:
4 new sperm cells
(1/2 of original # chromosomes)
Spermatogenesis
Females:
1 Egg Cell (3 polar bodies die off)
(1/2 of original chromosome #)
Oogenesis
1 egg cell produced
4 sperm cells produced
1. Reduces chromosome #
Humans 46
23
(getting ready for
fertilization!!!)
2. Variation (genetic differences)
What happens if
A mistake happens during
Meiosis?
-Chromosomal Abnormality
Ex:
Down Syndrome
47 chromosomes
Human Karyotype: A picture that pairs up a persons
chromosomes by size and shape
-Used by Geneticists to study chromosomes and determine genetic
disorders
Is this a male or a
female?
-Male
(one X chromosome
And one Y chromosome)
MITOSIS
MEOISIS
1
2
# Cell divisions:
# of Daughter
Cells Produced:
# of chromosomes
compared to parent:
Function of cells
produced:
(Type of cell)
Variation:
2
4
Same exact #
½ original #
Growth/Repair
(Body Cell)
Gamete (sex cell)
NO
(Clone)
YES
What would each daughter cell look like?
46
46
46
92
92
46
46
46
23
23
23
23
What is the purpose of mitosis?
-Growth and repair of BODY CELLS
What is the purpose of meiosis?
-Produce gametes (sex cells) for fertilization
(Reduces chromosome # and creates genetic variation)
*** No 2 sperm cells or egg cells are identical!!!
Are any two sexually reproducing individuals genetically
identical (except identical twins)?
-NO!!!
-Meiotic Variation
Process in which genetic material is exchanged
and switched during meiosis causing genetic
diversity within a species
How does variation occur?
3 Ways:
Crossing Over- During meiosis homologous genes are
Exchanged between homologous
chromosomes
Recombination- Due to crossing over, new genes are
created that neither parent had
Independent Assortment- Every time meiosis occurs, the
chromosomes line up in a
different order
What is the importance of variation?
-no two individuals within a species are identical
If we were all clones, one disease
could wipe us all out!!!!
Some advantages to sexual reproduction:
-Offspring is not identical to parent (Variation)
Why is fertilization important?
-transfers genes from BOTH parents to offspring
-Restores the chromosome number to normal
ONLY occurs in SEXUALLY reproducing organisms
Creates gametes (sperm and egg)
Creates BODY CELLS for growth and repair
of tissue (clones)
How do meiosis and fertilization work together to
carry out sexual reproduction ?
-Meiosis reduces the chromosome number by
½, creating gametes (sperm and egg)
-Fertilization restores the chromosome # back to normal
(sperm + egg = zygote with NORMAL # of chromosomes)