Video #1: Generations-Mitosis & Meiosis
In the mid 1800’s what did Pasteur, Lister do? In 1876, What did Walter
Flemming do that provided better visualization of parts in the cell?
What did he see & discover?
2.
Chromosomes literally mean: “_______”
3.
What is a centromere and what is its function?
4.
What is a karyotype and what does it reveal? What are “homologous
chromosomes”?
5.
How many chromosomes do humans, fruit flies (Drosophila), horsetails,
Toads, and pea plants have?
6.
Name the business used in the 2nd segment to show the importance of
mitosis.
7.
Briefly explain what “grafting” is?
8.
A complete cycle can be completed in about ______hrs in a rapidly
dividing tissue such as bone marrow. During this time mitosis occurs for
only _______ hr(s). Pg. 221
9.
Name the FOUR phases of Mitosis and two key events that occur. (See
pg. 222-223)
10. Name two differences between Mitosis & Meiosis after watching the final
segment.
****Write the Title for each segment and THREE key statements for each
segment.
1.
Introductory Questions #1
1) How much DNA does a typical human cell have?
How are chromosomes differ from chromatin?
2) How is a somatic cell different from a gamete?
3) How is every species different in regards to their
chromosomes?
4) Name the main stages of the cell cycle. (pg. 221)
5) What are the four stages of mitosis? Which stage
is the longest and which stage is the shortest?
6) Give three specific events that occur during
prophase. How is Prometaphase different from
prophase?
7) How are plant cell different from animal cells when
they divide?
Introductory Questions #2
1) What are the three checkpoints of the cell cycle that
regulates mitosis? Which one is considered the “restriction
point”? Why this checkpoint and not the others?
2) Name the two protein molecules that are high in
concentration during the mitotic (M) phase of the cell cycle.
Name the complex that it forms.
3) Why are telomeres considered to be a “mitotic clock”? DO
telomeres contain genes? What does telomerase do?
(see pgs 306-307 in Ch. 16)
4) How are tumor supressor genes different from an
oncogenes? How is a proto-oncogene different from an
oncogene? What kind of a protein does the RAS gene
produce?
5) What is the difference between a malignant tumor and a
benign tumor?
6) When looking at the hypothetical sequence of how mitosis
may have evolved how is the process different in a
bacteria and diatom from a plant and animal cell?
Introductory Questions #3
1)
2)
3)
4)
5)
6)
7)
How is a totipotent stem cell different from a pluripotent stem
cell? See pgs. 415-418 (Ch. 21)
Which phase is used to obtain pictures of chromosomes in
order to generate a karyotype
Give five differences between Mitosis and Meiosis.
Name three factors in Meiosis & reproduction that
contributes in increasing genetic variability within a
population.
What is a polar body? How is oogenesis different from
spematogenesis?
How is a sporophyte different from a gametophyte? What do
they produce and what process is involved, mitosis or
meiosis?
What is a tetrad? Which phase of Meiosis does crossing over
occur?
Mitosis and Meiosis
• Chapter 12 & 13
• Mitosis & Meiosis
Next Unit: Genetics & DNA
• Chapter 12 & 13: Mitosis & Meiosis
• Chapter 14: Principles of Heredity
• Chapter 15: Human Genetics &
Disorders
• **Two Labs will be done for this Unit
• Goal: to complete before Thanksgiving and to
take Test #3 on 11/25 (Tuesday)
Mitosis
• Occurs only in certain types of cells
• Form of asexual reproduction
• Produces two genetically identical cells
from one cell.
• The splitting or dividing of the nucleus
• Viewed in different stages by examining
chromosome formation and behavior.
Significance of Understanding Mitosis
• Preserves the continuity of life
• Allows organisms to grow, repair, and
reproduce
• Important in unlocking the mysteries of
embryonic development & stem cells
• Important in understanding how cancer
develops and could someday provide
clues in stopping cancer.
• Cell replacement (seen here in skin)
Dead
cells
Epidermis,
the outer
layer of the
skin
Dividing
cells
Dermis
Figure 8.11B
Packaging of Genetic Material
http://www.biostudio.com/demo_freeman_dna_coiling.htm
•
•
•
•
•
•
Structure / Activity
Diameter
DNA: smallest structure about (2 nm)
DNA & Histones = Nucleosome (10 nm)
Chromatin Fibers**
(30 nm)
Extensive Looping
(300 nm)
Further Condensing
(700 nm)
Fully Formed Chromosome (1400 nm)
Chromosomes
• Condensed DNA attached to proteins
• Can only be seen when a cell is actively
undergoing mitosis.
• Typical humans form 46 chromosomes vs. other
organisms which varies significantly.
• Our 46 chromosomes are thought to contain
anywhere from 25,000 to 100,000 genes.
• Duplicated before mitosis occurs producing a
sister chromatid (identical copy)
• Sister chromatids held together by “Centromere”
Cells from an onion Root tip
• When the cell cycle operates normally,
mitotic cell division functions in:
– Growth (seen here in an onion root)
Figure 8.11A
• E. coli dividing
Figure 8.3x
• Asexual reproduction (seen here in a hydra)
Figure 8.11C
MITOSIS
• A eukaryotic cell has many more genes
than a prokaryotic cell
– The genes are grouped into
multiple chromosomes,
found in the nucleus
– The chromosomes of this
plant cell are stained
dark purple
Figure 8.4A
• Human male bands
Figure 8.19x3
• Human female karyotype
Figure 8.19x2
Sister chromatids
• Before a cell starts
dividing, the
chromosomes are
duplicated
Centromere
– This process
produces sister
chromatids
Figure 8.4B
• When the cell
divides, the sister
chromatids
separate
Chromosome
duplication
Sister
chromatids
Centromere
– Two daughter
cells are
produced
– Each has a
complete and
identical set of
chromosomes
Chromosome
distribution
to
daughter
cells
Figure 8.4C
Interphase
Interphase
•
•
•
•
•
•
Cells spend most of its time in this phase
Cells are growing
DNA has to be replicated (all 2 meters of it)
Proteins are being produced
90% of all cells are in this phase
Three phases:
G1, S, and G2
Prophase
Prophase
• Chromatin thickens (coils) into chromosomes
• Two copies of DNA are present: sister chromatids
(twice the amount of DNA is present)
• Centrioles replicate forming another centrosome
separate.
• Centrioles separate to each side of the nucleus
• Nuclear membrane (envelope) disappears
• Microtubules elongate forming the spindle apparatus
Metaphase
Metaphase
• Chromosomes align themselves up in the
center of the cell
• Spindle fibers (microtubules) attach to the
centromere of the chromosomes
• Longest phase of Mitosis
Metaphase
• Mitotic spindle
Figure 8.6x2
Anaphase - Early & Late
Anaphase
• Chromosomes separate by the shortening of
the microtubules.
• The sister chromatids separate to each side
(pole) of the cell. (humans: 46 to each side)
• The centrosome is located at each side of the
cell.
Telophase (Plant & Animal)
Cytokinesis: Plant vs Animal
Cells
• Cleavage furrow: animals cells
• Cell plate: Plant cells
Cytokinesis differs for plant and animal
cells
• In animals, cytokinesis
occurs by cleavage
– This process pinches
the cell apart
Cleavage
furrow
Cleavage
furrow
Figure 8.7A
Contracting ring of
microfilaments
Daughter cells
• In plants, a
membranous cell
plate splits the cell
in two
Cell plate
forming
Wall of
parent cell
Cell wall
Figure 8.7B
Vesicles containing
cell wall material
Daughter
nucleus
New cell wall
Cell plate
Daughter
cells
Cells from an onion Root tip
• When the cell cycle operates normally,
mitotic cell division functions in:
– Growth (seen here in an onion root)
Figure 8.11A
Whitefish-phases of Mitosis
Various phases of Mitosis-Plants
Which Phase is this?
• Sea urchin development
Figure 8.0x
• Cell cycle collage
Figure 8.5x
• Fibroblast growth
Figure 8.8x
Total Class Data for all Three
Classes: Fall 2005
Interphase Prophase Metaphase Anaphase Telophase
Total # of cells
11806
2451
386
264
516
% in each phase
77%
16%
3%
2%
3%
Time in each phase (min)
1102.3
228.8
36.0
24.6
48.2
Hours
18.4
3.8
0.6
0.4
0.8
Total Class Data for all Three
Classes: Fall 2006
Interphase Prophase Metaphase Anaphase Telophase
Total # of cells
% in each phase
Time in each phase (min)
Hours
18296
84%
1208.1
20.1
1821
8%
122.3
2.0
529
2%
35.2
0.6
461
2%
29.9
0.5
695
3%
44.5
0.7
The Cell Cycle: Generation Time
• Interphase: most of a cell’s life
(90%)
-G1: 1st gap of growth
-S phase: DNA is duplicated
(synthesized)
-G2 phase: 2nd gap of growth
• Mitosis: splitting of the nucleus (PMAT)
• Cytokinesis: separation of the cytoplasm
The cell cycle multiplies cells
• The cell cycle consists of two major phases:
– Interphase, where chromosomes duplicate
and cell parts
are made
– The mitotic
phase, when
cell division
occurs
Figure 8.5
See Pgs 222-223
INTERPHASE
PROPHASE
Prometaphase
Figure 8.6
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#
Nuclear
envelope
forming
Nucleolus
forming
The Kinetochores
• Located in the middle of each sister
chromatid.
• Microtubules attach and breakdown as the
sister chromatids are pulled to opposite
sides of the cell.
• See Research on Pg. 225
• Mitosis collage, light micrographs
Figure 8.6x1
Evolution of Mitosis (pg. 227)
Chromosomes attach
to the plasma
membrane
Chromosomes
attach to the nuclear
membrane
Pass through the nucleus
Spindle forms within
the nucleus
Regulation of Cell Division
• Driven by specific molecular signals
• Research has shown:
– Two cells in different phases causes the other to
be pushed into the next phases.
– Ex.
• S phase & G1 grown together will cause the G1 cell to
enter into the S phase immediately
• M phase cell & G1 cell will cause the G1 cell to enter
into the M phase immediately.
• There is an obvious control system in place.
Regulating Mitosis-Control System
(pg. 229-231)
• Most cells can divide up to 50 times
• Control of the Cell cycle involves three checkpoints
-G1 (most important checkpoint) = restriction point
(G0: non-dividing state)
-G2
-M phase
• Growth factors (proteins): Cyclins & Kinases
– Kinases: phosphorylate proteins, gives the go ahead
– Cdk: are kinases that must be attached to a cyclin to be activated
– MPF: Maturation promoting factor (Fig: pg. 230)
• Complex of kinase and cyclin
• Triggers the passage from G2 phase into M phase
• peaks during Metaphase
Growth factors signal the cell
cycle control system
• Proteins within the cell control the cell cycle
– Signals affecting critical checkpoints determine
whether the cell will go through a complete cycle
and divide
G1 checkpoint
Control
system
M checkpoint
G2 checkpoint
Figure 8.9A
Cyclin & Kinase effects on the cell
cycle.
• Animated link:
http://nobelprize.org/educational_games/m
edicine/2001/cellcycle.html
Video #2: Cancer and its Causes
Reference Pages:
Ch. 16 Pgs. 306-307
Ch. 19 pgs. 370-373
****While watching the video be sure to have a minimum of
15 key statements. Some of your statements should
address:
1. What was thought to be the cause of cancer in the earlier
years? What do we know today in regards to the causes of
cancer?
2. Differences between an Oncogene and a Tumor
suppressor gene and what these genes specifically do.
3. The RAS gene and p53 gene and what they do. Which
one is a proto-oncogene
4. Why is the p53 gene considered to be the “Guardian Angel
of the cell” Give three things that is does.
5. How has the study of Telomeres and the enzyme
Telomerase contributed to our knowledge of cancer.
Cyclin & MPF Concentrations
• The binding of growth factors to specific
receptors on the plasma membrane is
usually necessary for cell division
Growth factor
Plasma membrane
Receptor
protein
Signal
transduction
pathway
Figure 8.8B
Relay
proteins
G1 checkpoint
Cell cycle
control
system
Growth Factors that stimulate Cell
Division
PDGF: Platelet-derived growth factor causes
fibroblasts to divide in response to an
injury. Has been shown to be effective in
artificial conditions
Cytokinins: key hormone in plants that
promotes cell division
Mitotic Clock Mechanisms in Cells
Telomeres, Proteins, Cell size (SA), hormones, &
Growth factors
• Telomeres: Segments of DNA (200 repeated
sequences of nucleotides) are lost at the tips
of the chromosomes with each mitotic event.
– (Mitotic clock) the tips of chromosomes wear
down and lose DNA sequences over time.
– Six Nucleotide sequence repeated hundreds of
times
– 1,200 nucleotides are removed after each mitotic
event
Image of Telomeres-notice light
Blue Regions
Chromosomes in green &
Telomeres in yellow
Genes that are thought to cause Cancer
See Pgs: 371-372
• Oncogenes: a gene that increases cell
division and triggers cancerous
characteristics.
• Tumor Suppressor genes: a gene that
inactivates or inhibits cell division. Prevents
uncontrolled cell growth (cancer). It keeps
mitosis in check and controls the cell cycle.
• Failure of normal cell programmed death
(Apotosis) Pgs. 800 & 902
Anchorage, cell density, and
chemical growth factors affect cell
division
• Most animal cells divide only when
stimulated, and others not at all
• In laboratory cultures, most normal cells
divide only when attached to a surface
– They are anchorage dependent
• Cells continue dividing until they touch one
another
– This is called density-dependent inhibition
Cells anchor to dish surface and
divide.
When cells have formed a
complete single layer, they stop
dividing (density-dependent
inhibition).
If some cells are scraped away,
the remaining cells divide to fill
the dish with a single layer and
then stop (density-dependent
inhibition).
Figure 8.8A
• Growth factors are proteins secreted by
cells that stimulate other cells to divide
See pg. 232
After forming a single layer, cells
have stopped dividing.
Providing an additional supply of
growth factors stimulates further
cell division.
Figure 8.8B
• Malignant tumors can invade other tissues
and may kill the organism
Lymph
vessels
Tumor
Glandular
tissue
Metastasis
1
A tumor grows
from a single
cancer cell.
Figure 8.10
2
Cancer cells invade
neighboring tissue.
3
Cancer cells spread
through lymph and
blood vessels to other
parts of the body.
Growing out of control, cancer cells
produce Malignant tumors
• Cancer cells have abnormal cell cycles
– They divide excessively and can form abnormal
masses called tumors
• Radiation and chemotherapy are effective as
cancer treatments because they interfere
with cell division
• Breast cancer cell
Figure 8.10x1
• Mammograms
Figure 8.10x2
Anti-Cancer drugs
• Colchicine: blocks microtubules from forming
-binds & inhibits unpolymerized tubulin
-breakdown of microtubules occur
-polyploidy could occur
• Taxol: Found in the bark of yew trees
-blocks ovarian cancer from forming
http://www.ncl.ox.ac.uk/quicktime/taxol.html
Video #2: Cancer and its Causes
Reference Pages:
Ch. 16 Pgs. 306-307
Ch. 19 pgs. 370-373
****While watching the video be sure to have a minimum of
15 key statements. Some of your statements should
address:
1. What was thought to be the cause of cancer in the earlier
years? What do we know today in regards to the causes of
cancer?
2. Differences between an Oncogene and a Tumor
suppressor gene and what these genes specifically do.
3. The RAS gene and p53 gene and what they do. Which
one is a proto-oncogene
4. Why is the p53 gene considered to be the “Guardian Angel
of the cell” Give three things that is does.
5. How has the study of Telomeres and the enzyme
Telomerase contributed to our knowledge of cancer.
Lab #7-Rooting for Mitosis
Objective & goals: Prepare and mount a slide of onion root
cells in hopes of viewing and identifying the phases of
Mitosis.
-Cut off a approx. 1mm section of root tissue from rounded tip
of the root.
-One drop of 1M HCl & let stand for 4 min.
-Use a tissue or towel to wick up the acid.
-Cover the root tip with 1% Toluidine-set for 2 min.
-Blot around root and rinse several times by absorbing with
towel and rinsing with water until the water runs clear.
-Add one drop of water and place a cover slip on the sample
-Apply pressure & squash the tissue with your fingers or easer
end of a pencil. Be careful not to crack the cover slip or
slide.
-View under the microscope first with low power then high
power.
-Identify, draw and label the phases observed in your sample.
Lab #7 Part II: Viewing the Phases of Mitosis
in Professionally Prepared slides of Allium
(onion) root tip and Whitefish Blastula
**Look for all the phases of mitosis including interphase using the prepared
slides of plant and animal cells.
**Count how many cells are in each phase and write those counts in table
(#13)
**Draw & LABEL all key structures: cell (plasma) membrane, nuclear
membrane, chromosomes, nucleolus, and all phases: I P M A T
IMPORTANT NOTE: Be sure to find a region on the root tip that has all the
phases represented. This means one drawing for the onion root and one
for the whitefish blastula.
**Be sure to indicate the magnification, and source of the tissue (label on the
slide)
Finally: Find some images for these two tissues. Print and paste next to your
drawing. Again be sure to include all labels you had in your drawing.
Answer the Evaluation & Test Preparation Questions. Do the online quiz from
the website written on your lab (after quest. #6)
Stem Cells (pgs. 415-418)
• Undifferentiated cells
• Progenitor cells: partially specialized cell.
an intermediate between a stem cell and a
fully differentiated cell.
• Pluripotent cells: follows fewer pathways
that it can develop into.
• Totipotent cells: cells that are very early
in development when the zygote has
developed into a small ball of cells.
Cell Differentiation
http://learn.genetics.utah.edu/units/stemcells/whatissc/
Heredity, Life Cycles, and Meiosis
Chapter 13
Heredity
Heredity: the transmission of traits
from one generation to the next
Asexual reproduction: clones
Sexual reproduction: variation
Human life cycle:
23 pairs of homologous chromosomes
1 pair of sex chromosomes (X or Y)
and 22 pairs of autosomes;
Karyotype : Pix of chromosomes
-Gametes are haploid (n)
-All other cells (somatic) are diploid
(2n)
-Fertilization (syngamy) joining
(fusion)
of gametes to produce a zygote
Meiosis: cell division to produce
haploid gametes
• The human
life cycle
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
Figure 8.13
Video #1: Generations-Mitosis & Meiosis
In the mid 1800’s what did Paseur, Lister do? In 1876, What did Walter
Flemming do that provided better visualization of parts in the cell?
What did he see & discover?
2.
Chromosomes literally mean: “_______”
3.
What is a centromere and what is its function?
4.
What is a karyotype and what does it reveal? What are “homologous
chromosomes”?
5.
How many chromosomes do humans, fruit flies (Drosophila), horsetails,
Toads, and pea plants have?
6.
Name the business used in the 2nd segment to show the importance of
mitosis.
7.
Briefly explain what “grafting” is?
8.
A complete cycle can be completed in about ______hrs in a rapidly
dividing tissue such as bone marrow. During this time mitosis occurs for
only _______ hr(s). Pg. 221
9.
Name the FOUR phases of Mitosis and two key events that occur. (See
pg. 222-223)
10. Name two differences between Mitosis & Meiosis after watching the final
segment.
****Write the Title for each segment and THREE key statements for each
segment.
1.
Alternative Life Cycles
Fungi/some algae
-Meiosis produces haploid cells (n)
that divide by mitosis to produce
-Haploid (n) adults
(gametes produced by mitosis)
Plants/some algae
Do Alternation of generations:
2n = Sporophyte generation
n = Gametophyte generation
Meiosis occurs & produces spores:
Spores are haploid (n)
Spores divide by mitosis to generate
more haploid cells (n)
Gametes are produced by mitosis
which then fertilize into a
sporophyte (2n)
Meiosis
• Chromosome replicate
• 2 Cell divisions occur
(Meiosis I & Meiosis II)
• 4 daughter cells are
made all are (n): haploid
• Homologous Chrom’s
separate in meiosis I
• Meiosis II = Mitosis
(chromatids separate)
Homologous chromosomes carry
different versions of genes
• The differences between homologous
chromosomes are based on the fact that
they can carry different versions of a gene
(alleles) at corresponding loci
Homologous Chromosomes
(Are they identical?)
Tetrad (Bivalent)
♂ from father
from mother
Sister Chromatids
• Human female karyotype
Figure 8.19x2
• Human male karyotype
Figure 8.19x4
MEIOSIS I: Homologous chromosomes separate
INTERPHASE
Centrosomes
(with
centriole
pairs)
Nuclear
envelope
Figure 8.14, part 1
PROPHASE I
METAPHASE I
Microtubules
attached to
Spindle kinetochore
Sites of crossing over
Chromatin
Sister
chromatids
Tetrad
Metaphase
plate
Centromere
(with kinetochore)
ANAPHASE I
Sister chromatids
remain attached
Homologous
chromosomes separate
Crossing over further increases
genetic variability
• Crossing over is the exchange of
corresponding segments between two
homologous chromosomes
• Genetic recombination results from crossing
over during prophase I of meiosis
Tetrad
Chaisma
Centromere
Figure 8.18A
Synaptonemal Complex- Pg 213
• Protein that hold homologous chromosomes
together
• Thought to be involved in crossing over
events
Coat-color
genes
• How crossing over
leads to genetic
recombination
Eye-color
genes
Tetrad
(homologous pair of
chromosomes in synapsis)
1
Breakage of homologous chromatids
2
Joining of homologous chromatids
Chiasma
3
Separation of homologous
chromosomes at anaphase I
4
Separation of chromatids at
anaphase II and completion of meiosis
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Figure 8.18B
Gametes of four genetic types
Coat-color genes
Eye-color genes
Brown
Black
C
E
c
e
White
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
Figure 8.17A, B
C
E
C
E
c
e
c
e
Chromosomes of
the four gametes
Origins of Genetic Variation
(1) Independent assortment:
How they line up during metaphase I
Matters!!!
Homologous pairs of chromosomes
position and orient themselves
Randomly. (random positioning)
Different combinations are possible
when gametes are produced.
POSSIBILITY 1
POSSIBILITY 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1
Figure 8.16
Combination 2
Combination 3
Combination 4
Origins of Genetic Variation
(2) Crossing over (prophase I):
-the reciprocal exchange of
genetic material between
nonsister chromatids during
synapsis of meiosis I
(recombinant chromosomes)
(3) Random fertilization:
1 sperm (1 of 8 million possible
chromosome combinations) x 1
ovum (1 of 8 million different
possibilities) = 64 trillion diploid
combinations!
MEIOSIS II: Sister chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Cleavage
furrow
Sister
chromatids
separate
Figure 8.14, part 2
Haploid
daughter cells
forming
Meiosis vs. Mitosis
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• Synapsis/tetrad/chiasmat
a (prophase I)
• Homologous vs.
individual chromosomes
(metaphase I)
• Sister chromatids do not
separate (anaphase I)
• Meiosis I separates
homologous pairs of
chromosomes, not sister
chromatids of individual
chromosomes.
MITOSIS
MEIOSIS
PARENT CELL
(before chromosome replication)
Site of
crossing over
PROPHASE I
Tetrad formed
by synapsis of
homologous
chromosomes
PROPHASE
Duplicated
chromosome
(two sister chromatids)
METAPHASE
ANAPHASE
TELOPHASE
2n
Daughter cells
of mitosis
Figure 8.15
Chromosome
replication
Chromosome
replication
2n = 4
Chromosomes
align at the
metaphase plate
Tetrads
align at the
metaphase plate
Sister chromatids
separate during
anaphase
Homologous
chromosomes
separate
during
anaphase I;
sister
chromatids
remain together
2n
MEIOSIS I
METAPHASE I
ANAPHASE I
TELOPHASE I
Haploid
n=2
Daughter
cells of
meiosis I
No further
MEIOSIS II
chromosomal
replication; sister
chromatids
separate during
anaphase II
n
n
n
n
Daughter cells of meiosis II
The End
• Translocation
Figure 8.23Bx
• At fertilization, a sperm fuses with an egg,
forming a diploid zygote
– Repeated mitotic divisions lead to the
development of a mature adult
– The adult makes haploid gametes by meiosis
– All of these processes make up the sexual life
cycle of organisms
• The large number of possible arrangements
of chromosome pairs at metaphase I of
meiosis leads to many different
combinations of chromosomes in gametes
• Random fertilization also increases variation
in offspring
• Human female bands
Figure 8.19x1
• Human female karyotype
Figure 8.19x2
• Human male bands
Figure 8.19x3
• Human male karyotype
Figure 8.19x4
• Down syndrome karyotype
Figure 8.20Ax
• Klinefelter’s karyotype
Figure 8.22Ax
• XYY karyotype
Figure 8.22x