Biology 101
Fall, 2008
Week 1 – Introduction
Seed Magic,
Cells, Tissues, Leaves
Mitosis, Meiosis
Meet the TA’s for fall 2008
Beth Thomas
Chandra Emani
Xiangyu Shi
Angelie Misra
Lab Coordinator Tonna Harris Haller
Computer
Charlie Harris
Office
S
BIOLOGY 101 ! GENERAL INFORMATION ! Fall 2007
TEXTBOOK- Stern, Introductory Plant Biology, (9th Ed) 2002; Website: http://www.idmb.tamu.edu/biology101/
Harris-Haller, Biology 101 Lab Manual, 1st ed. 2008, Hayden-McNeil Publishing Co. Primary local sources for the Textbook
are Loupot’s (Northgate) and Traditions bookstores. If you purchase on line be sure to get the 9th edn - ISBN 0072909412
LECTURE- MWF 9:10 to 10:00 a.m. in Biol. Sciences Bldg. East (BSBE) Room 115. Lecture notes will be posted at:
http://www.idmb.tamu.edu/biology101/ Approximately 25 POPQUIZZES, each typically worth 1 to3 points, will be held in
class without prior notice! As they are totally BONUS points, the instructor has NO obligation to provide any prior
announcement of these quizzes, and there here will be NO opportunities to make-up these quizzes. Attendance for the lectures
IS NOT mandatory but absence means that the opportunity for extra credits from POPQUIZZES will be lost.
LABORATORY- All lab sections meet in Heldenfels 305. Unlike lectures, attendance at the laboratories IS mandatory. There
are no makeup labs. If you miss lab, you must notify your instructor within two class days and provide documentation of a
university authorized absence within one week to be considered for a makeup assignment. See Lab Manual Appendix B for a 20
point bonus opportunity in lab:
EXAMS - DO NOT FORGET YOUR STUDENT ID! Exams I, II and III will be from 9:10 to 10:00 a.m. in BSBE 115, except
for students with disabilities. You may NOT take any back-pack, notes or headgear (e..g. caps) to your desk - leave them at the
side or front of the room. Exam I, Monday Sept 24; Exam II Friday Oct 19; Exam III; Monday Nov12. NOTE: Exam IV will be
from 8:00 to 10:00 (2 hr) on Monday, December 10. EXAM REVIEW SESSIONS - 7:30 to 9:00 p.m.: Thursday Sept 20;
Tuesday Oct 16; Thursday Nov 8 (all in BSBE 115). The review for the Final Exam (December 3) will be in normal class time
and place. MISSED EXAM If you know you will miss an exam for a university approved reason, please contact Dr. Hall as
soon as possible and in any case no less than 2 working days prior to the exam. If you miss an exam, you must show written
evidence within 1 week to substantiate the absence was for an accepted reason (section 7, Attendance, revised 2006
http://student-rules.tamu.edu/). The Lower Division Biology Program DOES NOT accept the Texas A&M University
Explanatory Statement of Absence Form as an excused absence. MAKE-UP EXAMS will NOT be rescheduled without
instructor permission and proof of an authorized absence. It is your responsibility to notify Dr. Hall of your absence, provide
verification, and insure your name is on the sign-up list for the appropriate make-up exam. Make-up exams will only be offered
on the following dates: (1) Thurs. Oct. 11; (2) Thurs. Nov. 1; (3) Thurs. Nov. 29. Make-up exams may consist of essay and short
answer questions. All make up exams will be held at 7:00-8:00 p.m in Heldenfels 100.
DETERMINE YOUR GRADE AS FOLLOWS: Note: Of the total possible points (600), 170 will be earned in the
Laboratory.
LECTURE
3 lecture examinations, 100 points each
1 final examination (comprehensive)
Sub Total
300
130
430
LAB
Lab Quizzes/writeups, 12 at 10 points each
Two laboratory reports at 15 points each
Lab participation points
Sub Total
120
30
20
170
To determine your grade: Add points scored for Exams I through IV; add total lab points. To this total add the total PopQuiz
bonus points. Divide this total by 6 to get a % score. Normally, 90-100% = A; 80-89% = B; 70-79% = C and 60-69% = D.
COMPUTER ACCESS INFORMATION- Please note that grade checks and exam challenges can only be made by computer
application. Once you obtain a student ID with a universal identification number (UIN), then logon to http://gateway.tamu.edu/
to activate your Neo NetID. Grade information will be posted online on Vista/Blackboard. Use your NeoID to login at
http://elearning.tamu.edu to access your grades.
GRADE CHECKS & EXAM CHALLENGES - Requests for grade checks must be submitted via the Lower Division Biology
Homepage at: http://www.bio.tamu.edu/ldi. You will be notified by email when a grade check is ready for pickup. Come to 315
Heldenfels and show your I.D. to pickup a grade check. Exam challenges are submitted via an Exam Challenge Form at:
http://www.bio.tamu.edu/ldi. All exam challenge forms will be forwarded to Dr. Hall for review.
ACADEMIC INTEGRITY: – “An Aggie does not lie, cheat or steal or tolerate those who do”. The Honors Council
provides a means to report and appeal allegations of academic dishonesty. Please see the Rules and Procedures at
http://www.tamu.edu/aggiehonor.
Misconduct in research or scholarship includes fabrication, falsification, or plagiarism in proposing, performing, reviewing or
reporting research. It does not include honest error or honest differences in interpretations or judgements of data. Texas A&M
University students are responsible for authenticating all work submitted to an instructor. If asked, students must be able to
produce proof that the item submitted is indeed the work of the student. Students must keep appropriate records at all times. The
1
BIOLOGY 101 ! LECTURE AND LAB SCHEDULE ! Fall 2007
BIOL 101 (3-3): MWF 9:10-10 a.m., BSBE 115
LAB: Heldenfels 305
INSTRUCTOR: Dr. Tim Hall tim@idmb.tamu.edu
OFFICE HOURS: W 10:15 am; F 2:00 pm
OFFICE LOCATION:
BSBW 407
OFFICE PHONE: 845-7728
BOOKS & RESOURCES: TEXT: Stern, Introductory Plant Biology 9th ed; Website:
http://www.idmb.tamu.edu/biology101/;
LAB: Harris-Haller, Biology 101 Lab Manual, 1st ed. 2008, Hayden-McNeil Publishing
Lecture Schedule and Subject
ì
Aug
Sep
Ù
Ú
Û
Text Chapters (Pages)
27 M Introduction
29 W Seeds - Morphology, germination
31 F Seedlings -roots, stems, leaves, (Tissues)
3 M Roots and Soils
5 W Stems, Secondary growth
7 F Leaves
10 M Flowering plants; Flowers
12 W Fruits and Seeds
14 F Classification Systems; Evol. concepts
17 M Cell Cycle, Mitosis, Meiosis
19 W Biomolecules (DNA & RNA) Replication
20 R Exam Review - 7:30 to 9:00 p.m.
21 F Growth & Dev. Hormones, Tropisms
Ü
24 M ** EXAM I ** (to Replication)
26 W Plant Metabolism: Carbohydrates, Lipids
28 F Membranes and membrane transport
Oct
1 M Photosynthesis - Light & dark (C3, C4)
3 W Respiration aerobic & anaerobic
5 F Genetics
Ý
Þ
ß
à
á
Nov
ìì
ìí
Lab Manual Exercis
Week 1 notes on Website; 1 (1-11) 1. Investigating Botany;
8 (147-153); 3 (28-50)
2. Cells
4 (53-64)
Seed germination setup
5 (65-85)
6 (86-108)
7 (109-129)
3. Flowering Plant Developm
Turn in notes on germinati
23 (441-460)
8 (130-147)
15 (273-285); 16 (286-298)
4. Flowering Plant Anatomy
Turn in notes on seedling d
12 (221-229)
11 (197-220)
5. Cell Division
extra credit: appendix B.
Field Botany/Campus Tou
10 (170-182)
6. Enzymes
2 (12-23); Website
Website; 9 (154-159)
10 (170-182; 182-186)
10 (186-196)
13 (231; 240-252)
7. Photosynthesis
8 M Gene structure, Transcription
10 W Amino acids, Protein synthesis (translation)
12 F Gene Cloning/synthesis and detection - PCR
Website; 13 (232-237)
8. Respiration
15 M Plant Tissue Culture
16 T Exam Review - 7:30 to 9:00 p.m.
17 W Plant transformation, regeneration
19 F **EXAM II ** (to Photosynthesis)
Protista-Algae
Website; 14 (253-272)
22 M Transgenic Plants: Analysis
24 W Feeding the world - 2005
26 F Feeding the world - 2050
29 M Plant pathogens and ways to stop them
31 W Algae
2 F Bryophytes
5 M Seedless Vascular Plants
7 W Seed Plants: Gymnosperms
8 R Exam Review - 7:30 to 9:00 p.m.
9 F Plant nutrition
12 M **EXAM III ** (Biotech/Alga-Gymnos)
14 W Nutrient cycles
16 F Ecology
9. Genetics
Website
24 (461-486)
Website
10. Transgenic Plants week 1
Website; 13 (237-241)
Website
Website
10. Transgenic Plants week 2
GFP Demo
11. Protein Synthesis
20 (381-395)
21 (410-420; 405-410)
12. Plant Pathogens
Website
13. Non-seed bearing plants
25 (487-507)
25 (508-518)
BIOL 101 LABS WILL BE HELD
THIS WEEK
e.g.
TODAY!
2
Several cultivars of common bean, Phaseolus vulgaris.
A “cultivar” or “cultivated variety” is not the same thing as a species,
but further changes could make it a species.
Some seeds are boring
Some seeds
are
interesting!
Seed Magic. How does a seed know when to germinate?
How do some parts grow up and some down?
Mung
2 days
Soy
3
Mung
3 days
Mung
6 days
Mung
Soy
Soy
Soya
4
SEED GERMINATION
„ primary growth
from apical
meristems of root
(radicle) and shoot
„ energy for growth
from:
„ endosperm
„ cotyledons
(storage proteins)
Bean seed structure, germination and seedling
Corn seed structure, germination and seedling
5
Mung seedling
leaves at 6 days
EMBRYO AND
SEEDLING
„ cotyledonary
node
„ epicotyl
„ hypocotyl
„ radicle
6
PLANT CELLS
1665 Robert Hooke - First to describe the concept of cells. He
actually studied cork, which only has dead cells.
1809 Jean Baptiste de Lamarck - Recognized that animals and
plants consisted of cells, often grouped into tissues.
1831 Robert Brown - Discovered the nucleus. Soon after,
Matthaias Schleiden discovered the nucleolus and, together with
Theodore Schwann, recognized the significance of cells and are
credited with developing (1838-39) the cell theory.
Robert Hooke 1635-1703
Lamarck 1744-1829
7
MEASUREMENT
ƒ METER (m)
ƒBasic unit of scientific measurement
ƒ CENTIMETER (cm)
ƒ0.01, 10-2 or 1/100th of a meter
ƒ MILLIMETER (mm)
ƒ 0.001, 10-3 or 1/1000th of a meter
ƒ MICROMETER (μm)
ƒ10-6, one millionth of a meter
ƒ NANOMETER (nm)
ƒ10-9, one thousand millionth of a meter
MEASUREMENT
ƒ MICROMETER (μm, micron)
ƒ10-6, one millionth, of a meter
A frequently used dimension in biology
Plant cell average size is 10 to 100 μm
Plant cell nuclei average 10 μm
Bacteria average
2 to 3 μm
Viruses are about
0.01 μm
Microtubule diameter is 0.02 μm
PLANT CELLS
8
The Plant Cell
Tonoplast
Vacuole
Nuclear Envelope
Microtubules
Chromatin
Mitochondrion
Nucleolus
Ribosomes
Rough ER
Actin
Filaments
Smooth ER
Chloroplast
Peroxisome
Plasmodesmata
Cell Wall
Plasma Membrane
Golgi Apparatus
Nucleus: contains chromosomes - DNA
(deoxyribonucleic acid) and proteins
Nucleolus
Nucleoplasm
Inner
Membrane
Nuclear
Pores
Nuclear
Pore
Outer
Membrane
Nuclear Envelope
DNA is typically wrapped round
histone proteins as chromatin..
Genes (DNA) are organized into
chromosomes.
Chromosomal structure is important in
cell division and in controlling gene
expression.
Nuclear products such as messenger
RNA (mRNA) are exported to the
cytoplasm via the nuclear pores.
Regulatory proteins and other
materials produced in the cytoplasm
are imported via nuclear pores.
Nuclear structure
Ribosomes, essential for protein
synthesis, are produced in the
nucleolus.
9
Cytoplasm
„ entire contents of
cell, except nucleus
„ cytosol
„ cytoskeleton –
network of filaments
„ Cytoskeleton Filaments
„ Microtubules: hollow tubules,
α- and β- tubulin, bound as dimers
MICROTUBULE
25 nm
α- and β- tubulin
„ Cytoskeleton Filaments
„ Actin filaments: two intertwined
actin strands
ACTIN FILAMENT
7 nm
Actin molecules
10
„ Cytoskeleton Filaments
„ Intermediate filaments: various fibrous
proteins
INTERMEDIATE FILAMENT
10 nm
Cytoskeleton
MICROTUBULE
ACTIN
FILAMENT
Cell Wall
„ middle lamella - holds cells together;
mostly pectins
„ primary cell wall - thin, flexible;
hemicellulose, pectin and glycoproteins
<25% cellulose
„ secondary cell wall - rigid, provides structure;
40 to 80% cellulose, up to 25% lignin
11
Cell Wall
Primary
Cell Wall
Layers of
Secondary
Cell Wall
Middle
Lamella
Plasmodesmata
From: Lucas et al. (2001) Nature Reviews Mol. Cell Biol. 2: 849-857
12
Plasma Membrane
surrounds cytoplasm
typically in contact
with cell wall
differentially
permeable
plasmodesmata
desmotubule
Plasma Membrane
„ made of phospholipids and proteins
Endoplasmic Reticulum (ER)
Rough ER
„ has ribosomes attached
„ ribosomes
„ are composed of RNA and protein
„ synthesized in the nucleolus
„ are the machinery for protein synthesis
Smooth ER
„ does not have ribosomes attached
13
Endoplasmic Reticulum (ER)
Golgi Bodies (Dictyosomes)
„ stacks of vesicles
„ receive material from ER
„ processed material exported to plasma membrane
and cell wall (exocytosis)
Chloroplast
Outer
Membrane
Thylakoid
Inner Granum
Stroma Membrane
Membrane
14
Chloroplasts
„ green organelles
surrounded by two
membranes
„ photosynthesis - light energy
harvested and converted into
chemical energy (sugars) by
fixation of atmospheric CO2
Mitochondria
„ two membranes; inner folded to form cristae
Cristae
Inner
Membrane
„ respiration –
chemical energy
(e.g. sugars)
is converted into ATP
(adenosine triphosphate)
and the ATP used for
cellular work;
CO2 released
Outer
Membrane
Vacuoles
„ surrounded by single membrane, the tonoplast
„ plant
turgidity
„ reservoir for
cellular
metabolites
15
MICROBODIES
„ small organelles (0.5 - 1.5 μm diameter)
„ single membrane
„ Peroxisomes
„ mainly in leaves
„ metabolize H2O2 (hydrogen peroxide) via catalase
„ contain oxidases that produce H2O2
„ Glyoxysomes - convert lipids to carbohydrates
(rare in animals)
The Plant Cell
Tonoplast
Vacuole
Nuclear Envelope
Microtubules
Chromatin
Mitochondrion
Nucleolus
Ribosomes
Rough ER
Actin
Filaments
Smooth ER
Chloroplast
Peroxisome
Plasmodesmata
Cell Wall
Plasma Membrane
Golgi Apparatus
Plant Tissues
A useful link is:
University of Arkansas at Little Rock
http://www.ualr.edu/botany/
16
Fundamental Types of Plant Cells
• Parenchyma – thin, primary cell walls;
undifferentiated, living
Parenchyma
„ chlorenchyma
„ photosynthesis
„ aerenchyma
„ gas exchange
„ transfer cells
„ short-distance
solute transport
„ storage parenchyma
Fundamental Types of Plant Cells
„ Collenchyma – unevenly thickened,
stretchable, primary cell walls; living
17
Fundamental Types of Plant Cells
• Sclerenchyma – thick, non-stretchable secondary
cell walls; dead
Sclerenchyma
„ Sclereids : short,
variously shaped
„ in all parts of the
plant
„ Fibers: long, slender
cells
„ often associated
with vascular bundles
18
Primary Types of Plant Tissues
„ MERISTEMS
„ Apical
„ Axillary buds
„ Intercalary
„ DERMAL TISSUES
„ Epidermis
„GROUND TISSUES
„Parenchyma
„Collenchyma
„Sclerenchyma
„ VASCULAR TISSUES
„ Xylem
„ Phloem
LEAVES
EXTERNAL STRUCTURE
„Simple leaves
„ flat, undivided blade
midvein
„ Compound leaves
„ blades divided into
leaflets
„ Both types supported by a petiole
(leaves with no petiole are sessile)
„ and sometimes subtended by bracts
19
Components of a typical leaf
cuticle
upper epidermal cell
palisade mesophyll
air space
spongy mesophyll
bundle sheath cell
vascular bundle
lower epidermis
stoma
guard cell
cuticle
petiole
blade
LEAF STRUCTURE
„ Epidermis
„ usually not photosynthetic – except for guard cells
„stomata
„ usually more on
abaxial than adaxial
surface
20
LEAVES: primary site of photosynthesis in
most plants
Leaf
design:
„ sunlight
„ CO2
„ water
„ sugars
(photosynthate)
INTERNAL STRUCTURE
Vascular tissues
„ veins
„ surrounded by
bundle sheath
INTERNAL STRUCTURE
„ Horizontal leaves
„ chlorenchyma cells
„ palisade mesophyll
„ aerenchyma cells
„ spongy mesophyll
„ Vertical leaves
„ uniform mesophyll
21
LEAF ABSCISSION
„ Deciduous plants
„ shed leaves in fall
„ fall colors
„ Evergreen plants
„ leaves live 3-5 years
„ shed year-round
stem
LEAF ABSCISSION : shedding of leaves
„ hormone controlled
„ short day length
„ drought
„ abscission zone
„ petiole base
„ little sclerenchyma
„ suberization (suberin)
„ suberized leaf scar
22
Palmately compound (Buckeye)
Pinnately compound (Black walnut)
Alternate (Tulip tree)
Opposite (Dogwood)
Palmately veined (Maple)
Globe-shaped (String-of pearls)
Pinnately veined (Oak)
Parallel-veined (Grass)
Whorled (Bedstraw)
Linear (Yew)
Fan-shaped (Ginkgo)
MODIFIED LEAVES
„ LEAF TENDRILS
„ e.g. garden peas
„STIPULES
„ protect buds (oak)
„ may become
tendrils (Smilax) or
spines (Euphorbia)
MODIFIED LEAVES
„ BUD SCALES
„ WINDOW
LEAVES
„ e.g. Fenestraria
23
MODIFIED LEAVES
Flower pot leaves
e.g. Dischidia
An epiphyte. Some leaves
develop into pouches.
Ants carry soil into the
pouches and moisture makes
a good growing medium.
developing roots
MODIFIED LEAVES
sundew (Drosera)
droplets of digestive enzymes
trap insects
pitcher plant (Sarracenia)
nectar glands attract insects,
they fall into pitcher
bladderwort (Utrichularia)
insects are sucked into bladders; trapdoor closes in 1/100 sec
Copyright © McGraw-Hill Companies
MODIFIED LEAVES
„ INSECT TRAPPING
LEAVES
„ e.g. Venus flytrap,
Dionaea
„ STORAGE
„ e.g. onion, Allium
24
MODIFIED LEAVES
„ COTYLEDONS
„ REPRODUCTIVE
„ asexual
„ e.g., Kalanchoë
MODIFIED LEAVES
„ SPINES
„ e.g. cacti
„ BRACTS
„ at base of flower
or peduncle
„ e.g.,
bougainvillea
Spines
Barbary (Berberis)
spines are modified
leaves
25
Thorns
Thorns are modified
stems produced in leaf
axils
Prickles
Rose (Rosa) prickles are
outgrowths of the stem
epidermis or cortex
LEAF DEFENSE SYSTEMS
„ Poisons
„ e.g. epidermal hairs with toxins
26
LEAF DEFENSE SYSTEMS
„ Protease inhibitors
in tomato – insect
damage to leaves
induces their
production
„ Hormones
Bugleweed (Ajuga
remota) produces
ecdysone-like
compounds that cause
insects to develop
multiple head
capsules
ECONOMIC IMPORTANCE OF LEAVES
„ Food,
spices, drinks
ECONOMIC IMPORTANCE OF LEAVES
„ Dyes
„ e.g. henna,
indigo
„ Fibers
„ Drugs
27
ECONOMIC IMPORTANCE OF LEAVES
„ Drugs
ECONOMIC IMPORTANCE OF LEAVES
„ Waxes, soaps
„ Fuel
„ coal
EXTERNAL SECRETORY STRUCTURES
„ Nectaries
„ Hydathodes
„ guttation
28
EXTERNAL SECRETORY STRUCTURES
„ Digestive
glands
„ trichomes
„ Salt glands
INTERNAL SECRETORY STRUCTURES
Secretory cells
„ chemical deterrents
„ sources of oils
„ peanut cotyledons
„ safflower seeds
„ palm fruits
„ secondary
phloem (bark) of
Cinnamomum sp.
INTERNAL SECRETORY STRUCTURES
„ Ducts
„ pine resin
„ deters
grazing
animals
„ seals
wounds
„ Laticifers
„ latex
29
MODIFIED LEAVES
sundew (Drosera)
droplets of digestive enzymes
trap insects
pitcher plant (Sarracenia)
nectar glands attract insects,
they fall into pitcher
bladderwort (Utrichularia)
insects are sucked into bladders; trapdoor closes in 1/100 sec
Copyright © McGraw-Hill Companies
Video gallery - cyclosis in
Canadian pondweed
by Dave Walker, UK
Elodea
30
The Cell Cycle
Mitosis and Meiosis
The Cell Cycle
„ Cell Growth
„ Interphase
„ G1
„S
„ G2
„ Cell Division
„ Mitosis
„ Cytokinesis
Telomere
31
http://highered.mcgraw-hill.com/sites/0073031216/student_view0/exercise13/mitosis_movie.html
„ INTERPHASE
„ period between cell
divisions
„ most metabolic activities
are conducted in this
phase
„ 90% of all cells are in this
phase
„ chromosomes elongated
as diffuse (eu)chromatin
„ INTERPHASE
„ G1 phase
„ cellular growth and
biosynthesis
„ proteins and enzymes
produced
„ organelles multiply
„ nucleotides made
„ cytoskeletal microtubules reassemble
32
„ INTERPHASE
„ S phase
„ DNA is synthesized (replicated)
„ G2 phase
„ cell prepares for mitosis
„ microtubule synthesis
„ proteins made for processing chromosomes
and lysis of the nuclear envelope
MITOSIS
The nucleus divides
to give two daughter nuclei
genetically identical to the
parental nucleus
The original ploidy
(haploid - n or diploid - 2n)
of the parental nucleus is
maintained
MITOSIS
„ Prophase
Chromatin condenses.
Chromosomes become
visible and easily stainable –
two chromatids can be
discerned.
Nuclear envelope dissolves.
Nucleolus gradually
disintegrates.
33
MITOSIS
„ Metaphase
The spindle apparatus,
composed of microtubules,
forms
Additional microtubules
attach to kinetochores on
either side of centromere to
complete the spindle
apparatus
Chromosomes align with
their centromeres on a single
equatorial plane: the
metaphase plate
MITOSIS
„ Anaphase
Centromeres split
Chromatids become
chromosomes as
they are pulled
(and/or pushed)
apart
MITOSIS
„ Telophase
The nuclear envelopes
surround new
chromosomes, forming
daughter nuclei
The chromosomes decondense
into diffuse euchromatin
34
Cytokinesis - Division of the Cytoplasm
Phragmoplast
system of
microtubules on the
plane of the former
preprophase band
and cell equator
Cytokinesis
„ dictyosome
vesicles
„ cell-wall
......precursors
Vesicles
„ trapped by the
phragmoplast
„ cell plate
„ becomes the new
cell wall
Cell Plate
Daughter
Cells
„ desmotubules (ER)
penetrate plate; form
plasmodesmata
MITOSIS
Mitotic Stages in the Endosperm of
Haemanthus katherinae,
Photographed with an Interference
Contrast Microscope
A. BAJER, Eugene/Oregon
b-online@botanik.uni-hamburg.de
35
MEIOSIS
„ 2 nuclear divisions
„ Meiosis I (1 → 2 cells)
Meiosis II (2 → 4 cells)
„ four haploid (1n) nuclei
from one diploid (2n)
nucleus
„ genetic information is
reassorted, yielding
genetic variation in
daughter nuclei
Meiosis I : Reduction Division (2n → n )
„ PROPHASE I
„ chromosomes
condense
„ homologous
chromosomes pair
(synapsis)
„ DNA is exchanged
between non-sister
chromatids at chiasmata
Meiotic Stages in Anthers of Ramsons (Allium ursinum; 2n = 14)
Staining with acetic acid carmine, phase contrast microscopy
photography by W. KASPRIK
© Peter v. Sengbusch - b-online@botanik.uni-hamburg.de
Meiosis I : Reduction Division (2n → n )
„ PROPHASE I
crossing-over and
gene exchange occur
No Chiasmata
Synapsis - synaptonemal
complex; bivalents
chiasmata form
exchange of genetic
information
Chiasmata
36
Meiosis I
„ METAPHASE I
„ homologous chromosome
alignment centromeres lie
on either side of the cell
equator
„ microtubules attach to
one side of each
centromere in bivalent
Meiosis I
„ ANAPHASE I
„ Chromosome
separation
(2n → n)
37
Meiosis I
„ TELOPHASE I
„may be
omitted in
meiosis
„ cytokinesis
may occur
Meiosis II: Gamete or Spore Formation
„ PROPHASE II
„ chromosome
condensation
„ omitted, if
Telophase I
was omitted
Meiosis II: Gamete or Spore Formation
„ METAPHASE II
„ chromosomal
alignment
„Cell equator–
usually oriented 90o
to first division
38
Meiosis II
„ ANAPHASE II
„ centromeres
split
„ chromatids
separate,
becoming
chromosomes
Meiosis II
„ TELOPHASE II
„ nuclear
envelopes
reform
„ chromosomes
decondense
Comparison of mitosis and meiosis
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Fig. 12.2f2
MEIOSIS
Produces four haploid (gametophyte) nuclei from one
diploid (sporophyte) nucleus
The number of chromosomes is halved (2n
Fertilization will restore the diploid state.
n).
During the process, genetic information is reassorted
Depending upon chromosomal arrangement during
metaphase I, two of the daughter nuclei can have the
majority of their genetic information from the female
grandparent
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