Cell Reproduction
Homework!
• www.cellsalive.com
• Complete the mitosis and meiosis sheets
Cells Division Introductory Video
• During cell division the
cell’s DNA is coiled
compactly into a
CHROMOSOME
• Each chromosome is a
single DNA molecule
• The DNA wraps tightly
around a protein called
HISTONE (helps maintain
the chromosome’s shape)
The
Chromosome
Breaking Down the Definitions
1.
2.
3.
4.
5.
6.
7.
8.
Chromosome
Histone
Chromatid
Centromere
Chromatin
Sex chromosome
Autosome
Homologous
chromosome
9. Karyotype
10. Diploid
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Haploid
Binary fission
Mitosis
Asexual reproduction
Meiosis
Gamete
Interphase
Cytokinesis
Prophase
Spindle fiber
Metaphase
22.
23.
24.
25.
26.
27.
28.
29.
Anaphase
Telophase
Cell plate
Synapsis
Tetrad
Crossing over
genetic recombination
Independent
assortment
30. Sexual reproduction
Anatomy of a Chromosome
• Each half of a chromosome is
called a CHROMATID
• Chromatids form as the DNA
copies itself before cell division
• The 2 Chromatids are attached at
a point called a CENTROMERE
• CHROMATIN=less tightly areas of
DNA between cell divisions
Chromosome Numbers
• Every species has a certain number of
chromosomes in each cell.
• Animal chromosomes are either:
• Sex Chromosomes—will determine the
gender of an organism (X and Y)
• Autosomes—all of the other
chromosomes
• Cells with 2 sets of Chromosomes are
DIPLOID
• Cells with one set of chromosomes are
HAPLOID (sex cells…half the number of
chromosomes)
Chromosomes Clip
• How many chromosomes does a potato have?
• How many chromosomes do Ferns have?
• After the video…in your own words why do different
organisms have different numbers of chromosomes??
Cell Division (aka Cell Reproduction) in
Prokaryotes
•Most prokaryotes
reproduce by BINARY
FISSION
•2 identical cells are
produced from one
cell
•Draw this
Cell Division Eukaryotes
• Two types of Cell Division
(Reproduction) in
Eukaryotes!
• Mitosis=new cells with
identical genetic material
• Meiosis=reduces the
number of chromosomes
by half for the purpose of
eventual reproduction
Mitosis
Meiosis
The Cell Cycle
• The CELL CYCLE
is the repeating
events of the life
of a cell.
• Interphase is the
period between
cell divisions
How do little elephants grow up to be BIG elephants?
Three reasons why cells reproduce by
asexual reproduction or MITOSIS:
1. Growth
2. Repair
3. Replacement
Mitosis Cycle
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase & Cytokinesis
Interphase
occurs before mitosis begins
• Chromosomes are copied (# doubles)
• Chromosomes appear as threadlike coils (chromatin) at the
start, but each chromosome and its copy(sister
chromosome) change to sister chromatids at end of this
phase
Nucleus
CELL
MEMBRANE
Cytoplasm
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase
1st step in Mitosis
• Mitosis begins (cell begins to divide)
• Centrioles (or poles) appear and begin to move to opposite
end of the cell.
• Spindle fibers form between the poles.
Centrioles
Sister chromatids
Spindle fibers
Prophase
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
2nd step in Mitosis
•Chromatids (or pairs of
chromosomes) attach to the spindle
fibers.
Centrioles
Spindle fibers
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
3rd step in Mitosis
• Chromatids (or pairs of chromosomes)
separate and begin to move to opposite
ends of the cell.
Centrioles
Spindle fibers
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase
4th step in Mitosis
• Two new nuclei form.
• Chromosomes appear as chromatin (threads rather than
rods).
• Mitosis ends.
Nuclei
Chromatin
Nuclei
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesis
occurs after mitosis
• Cell membrane moves inward to create
two daughter cells – each with its own
nucleus with identical chromosomes.
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
REMEMBER!
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
IPMATC
I P___ M___ A___ T___ C______
Label it!
Brainpop Mitosis
Mitosis in an
Onion
Stages of Mitosis Animation
It’s your turn! Identify the stages of mitosis…
Mitosis Dance Video
Onion Tips and Whitefish…
View 1
Whitefish
Onion
View 2
View 3
View 4
View 5
Meiosis – key differences from mitosis
• Meiosis reduces the number of chromosomes by half.
• Daughter cells differ from parent, and each other.
• Meiosis involves two divisions, Mitosis only one.
• Meiosis I involves:
• Synapsis – homologous chromosomes pair up. Chiasmata form
(crossing over of non-sister chromatids).
• In Metaphase I, homologous pairs line up at metaphase plate.
• In Anaphase I, sister chromatids do NOT separate.
• Overall, separation of homologous pairs of chromosomes, rather
than sister chromatids of individual chromosome.
Meiosis KM
42
Meiosis I (four phases)
• Cell division that reduces the chromosome number
by one-half.
• four phases:
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I
Meiosis
• The form of cell division by which gametes (sperm or egg cells), with
half the number of chromosomes, are produced.
• Diploid (2n)
haploid (n) n=# of chromosomes
• Meiosis is sexual reproduction.
• Two divisions (meiosis I and meiosis II).
Meiosis
• Sex cells divide to produce gametes (sperm or egg).
• Gametes have half the # of chromosomes.
• Occurs only in gonads (testes or ovaries).
Male: spermatogenesis
Female: oogenesis
• Meiosis is similar to mitosis with some chromosomal differences.
Sex Chromosomes
The Sex Chromosomes code for the sex of the offspring.
** If the offspring has two “X” chromosomes it will be a female.
** If the offspring has one “X” chromosome and one “Y” chromosome it will be
a male.
In Humans the
“Sex
Chromosomes”
are the 23rd set
XX chromosome - female
XY chromosome - male
Boy or Girl? The Y Chromosome “Decides”
Y chromosome
X chromosome
Interphase I
• Similar to mitosis interphase.
• Chromosomes replicate (S phase).
• Each duplicated chromosome consist of two identical
sister chromatids attached at their centromeres.
• Centriole pairs also replicate.
Interphase I
• Nucleus and nucleolus visible.
chromatin
nuclear
membrane
cell membrane
nucleolus
Prophase I
• Longest and most complex phase (90%).
• Chromosomes condense.
• Synapsis occurs: homologous chromosomes come
together to form a tetrad.
• Tetrad is two chromosomes or four chromatids (sister
and nonsister chromatids).
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
Prophase I
spindle fiber
aster
fibers
centrioles
Crossing Over
• Crossing over (variation) may occur between
nonsister chromatids
• Crossing over: segments of nonsister chromatids
break and reattach to the other chromatid.
Crossing Over - variation
nonsister chromatids
chiasmata: site
of crossing over
Tetrad
variation
Another Way Meiosis Makes Lots of
Different Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of
different gamete types produced by independent
Metaphase I
• Shortest phase
• Tetrads align on the metaphase plate.
• INDEPENDENT ASSORTMENT OCCURS:
1. The random separation of the homologous
chromosomes---this results in GENETIC VARIATION
Homologous Chromosomes
• Pair of chromosomes (maternal and paternal) that are similar in shape and
size.
• Homologous pairs (tetrads) carry genes controlling the same inherited traits.
• Each locus (position of a gene) is in the same position on homologues.
• Humans have 23 pairs of homologous chromosomes.
a.
b.
22 pairs of autosomes
01 pair of sex chromosomes
Homologous Chromosomes
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal
Metaphase I
OR
metaphase plate
metaphase plate
Anaphase I
• Homologous chromosomes separate and move towards the poles.
• Sister chromatids remain attached at their centromeres.
Anaphase I
Telophase I
• Each pole now has haploid set of chromosomes.
• Cytokinesis occurs and two haploid daughter cells
are formed.
Telophase I
Meiosis II
• No interphase II
(or very short - no more DNA replication)
• Remember: Meiosis II is similar to mitosis
Prophase II
• same as prophase in mitosis
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
Telophase II
• Same as telophase in mitosis.
• Nuclei form.
• Cytokinesis occurs.
• Remember:
four haploid daughter cells
produced.
gametes = sperm or egg
Telophase II
Meiosis
n=2
sex cell
sperm
n=2
n=2
2n=4
haploid (n)
n=2
diploid (2n)
n=2
n=2
meiosis I
meiosis II
Meiosis – mouse
Parent cell
1st division
2nd division
4 gametes
Meiosis I
Draw
This!
Meiosis
II
Meiosis
Cells Dividing Clip
Crash Course Meiosis
Meiosis Pipe Cleaner Lab
Snowball Fight!