CELL REPRODUCTION
Chapter 8
•CHROMOSOMES
•CELL DIVISION
•MEIOSIS
WHAT IS DNA?
• Deoxyribonucleic acid
• Long thin molecule
that stores genetic info
• In humans- 6 billion
pairs of nucleotides
• If a cell were the size
of a basketball, the
DNA would stretch for
40 miles!
CHROMOSOME
STRUCTURE
• DNA is coiled into
very compact
structures called
chromosomes.
• CHROMOSOMES
are rod-shaped
structures of DNA +
histone PROTEIN.
Replicated DNA
• Each half of the
chromosome is called a
CHROMATID.
(divide it vertically)
• Identical chromatids
formed during S phase
of the cell cycle ensure
that cell division will
result in indentical cells.
• They are connected at
the CENTROMERE.
Draw and label this chromosome
CHROMOSOME NUMBER
• Each species has a certain
number of chromosomes in each
cell.
• For each chromosome there are
two copies- one from Mom & one
from Dad.
• For example, humans have 46
and gorillas have 48!
• Cats, like mine… Pele, have 32
of them!
HOMOLOGOUS
Chromosomes
• Every cell of an
organism produced by
sexual reproduction has
two copies of each
autosome.
• Get one copy of each
autosome from each
parent.
• Two copies of each
chromosome that
contain the same genes
are called
KARYOTYPE photomicrograph of
all the chromosomes in the
nucleus of• AUTOSOMES
a cell are the
chromosomes besides
the sex chromosomesnumbered 1-22.
• In humans, 44
chromosomes are
AUTOSOMES and the
other 2 are sex
chromosomes.
• What sex chromosome
combination do males
have?
SEX chromosomes
• Sex Chromosomes
determine the sex of an
organism.
• In humans:
XX is female
XY is male
* This is why males
determine the sex of
the baby!
Haploid & Diploid Cells
• Haploid Cells (1n)
-have one of each
chromosome
-examples: sperm cells, egg
cells
• Diploid Cells (2n)
-have pairs of chromosomes
-examples: all non-reproductive
cells.
• Exception: red blood cells don’t
have any chromosomes
CELL DIVISION IN
PROKARYOTES
Prokaryotes have ONE chromosome that exists as a loop. They
also have no nuclear envelope separating their DNA from the rest
of the cell.
BINARY FISSION is the
division of a
prokaryotic cell
(bacteria) into two
identical cells!
1. DNA copied
2. Copies move
3. Cell membrane begins
to divide the cell in two
4. Two identical haploid
cells are formed.
CELL DIVISION IN
EUKARYOTES
is more complicated because the DNA is enclosed in a nuclear envelope, the
DNA is arranged in multiple strands, with a duplicate copy of each
• NUCLEUS divides (karyokinesis)
chromosome.
before the cell divides
(cytokinesis)
Two types:
1. MITOSIS (makes clones)
-reproduction of unicellular
organisms
-addition of cells to a tissue or
organ.
2. MEIOSIS (makes gametes)
-used for sexual reproduction
-1/2 as many chromosomes
-sperm & egg can recombine in
sexual reproduction.
THE CELL CYCLE
The events that occur in the “life” of a cell. The cell grows and
copies its’ DNA during Interphase (the longest phase), then divides
during M phase.
• INTERPHASE
- G1 (growth)
- S (DNA synthesis)
- G2 (growth)
• MITOSIS-nuclear division
- prophase
- metaphase
- anaphase
- telophase
• CYTOKINESIS-cytoplasmic
division
-cleavage furrow in animal
cells
Question: Where does the toy
poodle urinate when it is
raining outside?
• THE PMAT
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
MITOSIS & MEIOSIS
Chapter 8
MITOSIS
results in identical cells.
Behavior of chromosomes1. PROPHASE- replicated
in KARYOKINESIS is DNA condenses into
replicated chromosomes
simple:
(sister chromatids)
sister chromatids separate2. METAPHASE- replicated
chromosomes line up on
the metaphase plate
(imaginary center plane of
cell)
3. ANAPHASE- sister
chromatids are pulled
apart to opposite “poles”
of the cell.
4. TELOPHASE- nuclear
envelope reforms.
* CYTOKINESIS = 2 cells
Mitosis- produces identical
cells
MITOSIS
• Prophase
• Metaphase
• Anaphase
• Telophose
CYTOKINESIS
CYTOKINESIS
• Cleavage furrow
in Animal cells.
• Cell Plate in Plant
cells.
Can you name the stages and
the organelles involved???
MEIOSIS
• Process of nuclear division that reduces the number of
chromosomes in new cells to half the number in the
original cell.
• Chromosomes no longer in pairs.
• This 1/2ing of the chromosome number allows for the
fusion of cells later in the life cycle of the organism.
• The chromosome in one gamete can find its’ “pair” in
another gamete through the fusion of sperm & egg.
• In humans MEIOSIS results in either
-4 sperm cells from 1 sperm producing cell or
-1 egg cell & 3 polar bodies from 1 egg producing
cell
• Egg and Sperm combine chromosomes in sexual
GAMETES- haploid reproductive cells
SPERM (spermatogenesis) & EGGS (oogenesis
MEIOSIS ONE
homologous chromosomes
separate
Crossing over
Independent assortment
Genetic recombination
Occurs during meiosis 1:
1. Crossing Over
2. Independent assortment
STAGES OF MEIOSIS
MEIOSIS 1- homologous replicated chromosomes divide = pairs
are split.
Prophase 1- DNA condenses into chromosomes
Metaphase 1- tetrads align on the metaphase plate
Anaphase 1-homologous replicated chromosomes pulled Apart
Telophase 1-nuclei form…
Q: Cells are haploid or diploid at the end of meiosis 1?
A: HAPLOID
MEIOSIS 2- chromatids of the replicated chromosomes are
separated.
Prophase 2-DNA condenses into chromosomes
Metaphase 2-replicated chromosomes align on the metaphase
plate
Anaphase 2-chromatids separate
Telophase 2-nuclei form…
PROPHASE 1
• SYNAPSIS is the
pairing of homologous
chromosomes.
• TETRAD is each pair
of homologous
chromosomes.
• CROSSING OVER is
when portions of
chromatids break off
and attach to the
adjacent chromatid on
the homologous
chromosome.
• This results in
Crossing Over occurs during
PROPHASE 1 of MEIOSIS
• Homologous
chromosomes pair
up in a tetrad.
• Non sister
chromatids get
tangled and switch
places.
• RECOMBINANT
chromosomes are
created.
• = new
METAPHASE
• Tetrads align on the
metaphase plate.
• Spindle fibers from one
pair of centrioles
attach to one
replicated
chromosome of the
tetrad pair.
• Spindle fibers from the
other pair of centrioles
attach to the other
replicated
ANAPHASE 1
• INDEPENDENT
ASSORTMENT is the
random separation of the
homologous chromosomes
based on how the tetrads
line up during METAPHASE
• Think of it as “shuffling” the
chromosomes. There are
many different combinations
of the chromosomes
possible… each side gets
one out of two of each
chromosome.
• Independent assortment
happens during
ANAPHASE 1.
CAN YOU FIND THE
PATTERN?
1 pair of
chromosomes
2X1=2
2 kinds of
gametes
2 pairs
chromosomes
2X2=4
4 kinds of
gametes
3 pairs
Chromosomes
2X2X2=8
8 kinds of
gametes
4 pairs
chromosomes
2X2X2X2=16
16 kinds of
gametes
How many kinds of gametes for Humans w/ 23 pairs of chroms?
HOW MANY DIFFERENT
TYPES OF GAMETES CAN
YOU MAKE?
DID YOUR PARENTS MAKE
WHEN THEY MADE YOU?
WHY DOES THIS MATTER?
• FORMULA = (2) 23 or (2) # chromosomes
• 2 (because there are two copies of each
chromosome: one from mom & one from dad)
raised to the 23rd power (because humans have
23 chromosomes.)
• 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2
x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 =
8,388,608
• 1/8,388,608 x 1/8,388,608 =
• 1/70,368,744,180,000 = that your parents will have
another “YOU”
• YOU ARE SPECIAL!!!
Meiosis II
• CELLS ARE
HAPLOID
• Although,
chromosomes
are replicated.
• Is
ESSENTIALLY
mitosis.
• Chromatids
separate.
MEIOSIS TWO
sister chromatids separate =
similar to mitosis.
Note the difference… the cells are already haploid. Only one
Color of each kind of chromosome in each cell.
MITOSIS QUESTIONS 1-11
1. Cell cycle :
Interphase (G1, S, G2) 90% of the cell’s life. It
grows and during S phase it
copies/replicates it’s DNA)
M phase (P,M,A,T) Karyokinesis- division of the
nucleus. Replicated chromosomes line up
on the metaphase plate and Chromatids are
separated. Two identical nuclei are formed.
Cytokinesis- division of the cytoplasm via
cleavage furrow (microfillaments pulling like
a drawstring on sweatpants) in animal cells
and cell plate formation (cellulose delivered
by vesicles) in plant cells.
2) Fingers = spindle fibers
Hands = centrioles
Chromosomes don’t move on their own… the
microtubules formed by centrioles attach to
the centromeres of the replicated
chromosomes and move them around. :)
3) The chromosomes are NOT lined up in any
particular order during prophase of mitosis.
3)