Mendelian genetics and plant reproduction PS 353 Lecture 2 Chapter 2

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Mendelian genetics and plant reproduction PS 353
Lecture 2 Chapter 2

• Bob Trigiano

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Objectives and discussion questions

• There is a vocabulary that is necessary to master
  to understand basic plant genetics and
  reproduction.
• What is a gene, and why are there multiple viable
  definitions?
• How does the discrete nature of chromosomes
  impact sexual reproduction in plants?
• What would be the consequence of sexual
  reproduction if mitosis was the only form of cell
  division?
• How do the reproductive features of plants
  regulate the degree of inbreeding?

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• Alternation of Generations
• Mitosis and Meiosis
• Mendelian Genetics

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ALTERNATION OF GENERATIONS

• DEFINITIONS
• Diploid Having two sets of chromosomes or 2N
  the sporophyte phase of plants. 2N 2X 22
  (Flowering dogwood)
• Haploid Having one set of chromosomes or N the
  gametophyte phase of plants. N X11 (Flowering
  dogwood)
• Polyploid Having more than two sets of
  chromosomes 2N 6X 54 sporophyte
  gametophyte N 3X 27 (Chrysanthemum)

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How is Alternation of Generations Accomplished?
Mitosis (1 cell 2 cells) and Meiosis
(1 cell 4 cells) and Sexual
Reproduction where 1 1 2 1!
Gametophyte (n) mitosis Gametes
(N) fuse (sexual reproduction) to form zygote
(2N) mitosis Mature Sporophyte (2N)
meiosis
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ALTERNATION OF GENERATIONS
Higher Plants
Lower Plants
SHADED AREA REPRESENT RELATIVE TIME IN DIPLOID
OR SPOROPHYTIC PHASE OPEN RELATIVE TIME IN
HAPLOID OR GAMETOPHYTIC PHASE.
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1
MOSS
FERN
A
www.calflora.net
silviahartmann.com
D
E
A
B
D
C
C
B
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Mitosis and Meiosis
http//www.vcbio.science.ru.nl/images/cellcycle/mm
itosis_onion_zoom.jpg
http//www.phschool.com/science/biology_place/bioc
oach/index.html
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Figure 6.1
Structure of DNA Nitrogenous base (A, T, G,
and C) Phosphate Deoxyribose sugar
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Figure 6.3
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Figure 2.2
A. Chromosome Physical States
Nucleus
Nucleus
Condensed Chromosome
Relaxed Chromosome
B. Chromosome Conformations
C. Homologous Chromosomes
Chromatid
Sister Chromatids
DNA Synthesis
Locus 2
Centromere
Centromere
Locus 1
Chromosome 1
Chromosome 2
Chromosome 1
Chromosome 1
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http//nobelprize.org/nobel_prizes/medicine/laurea
tes/2001/cellcycle_eng.jpg
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STAGES OF MITOSIS
PROPHASE Shortening and thickening of
chromosomes (actually sister chromatids
Movement to the metaphase plate
nucleous disappears nuclear
membrane disappears. METAPHASE Chromosomes
lie on the plate. ANAPHASE Sister chromatids
separate and are pulled toward the
poles. TELOPHASE Last phase of mitosis
chromosomes become reorganized into nuclei
nucleolus reappears and
nuclear membrane is reformed. CYTOKINESIS
Literally division of the cytoplasm (including
organelles such mito-
chondria, chloroplasts, etc.).
Essentially, mitosis is asexual division
(formation of somatic cells and builds the
plants. Theoretically, all cells resulting from
mitosis are clones not quite true, but close
enough for our purposes.
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http//tainano.com/Molecular20Biology20Glossary.
files/image011.gif
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Onion Root Tip
1 Interphase, 2-5 Prophase 6 Early
Metaphase 7 Late Metaphase 8 Anaphase 9
Telophase 10 Completion of Cytokinesis
http//www.vcbio.science.ru.nl/images/cellcycle/mm
itosis_onion_zoom.jpg
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Figure 2.7. Mitosis
Metaphase Plate
Nucleus
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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OH NO ! MORE DEFINITIONS
Meiosis Two successive divisions (reduction
followed by an equal) that reduces the ploidy
level from 2N to N or diploid to
haploid. Homologous Chromosomes Chromosomes
that associate in pairs in the first division of
meiosis each member of the pair was derived from
a different parent. Crossing Over The exchange
of corresponding segments of genetic material
between chromatids of homologous chromosomes.
See also Synapse and Chiasma Recombination
The process by which offspring can gain
combination of genes different from the
combinations in either of their parents. Leads
to genetic diversity.
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Stages of Meiosis
Prophase I Same as in mitosis except that
crossing over occurs here. Metaphase I
Homologous chromosomes (each chromosome consists
of 2 sister chromatids) line up opposite each
other on the plate. Anaphase I One of each of
the homologous pair of chromosomes are drawn to
the two poles. This essentially reduces the
number of chromosomes that are in each cell by
half. Diploid Haploid. Telophase I
Haploid cells are established chromosomes
disappear. Prophase II Chromosome condense
(sister chromatids are not identical to one
another because of crossing over). Metaphase II
Chromosomes (actually sister chromatids) align on
the plate. Anaphase II One sister chromatid
(now chromosome) are drawn to each pole.
Teleophase II and Cytokinesis Essentially the
same as in mitosis.
Meiosis is essentially a reduction division
followed by an equal division. Tetrad (4) of
cells or spores are formed.
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Figure 2.9. Crossing over
A.
B.
C.
Chiasma - Exchange between homologous
chromosomes. Actually sister chromatids during
Prophase I.
Synapse pairing of homologous Chromosomes
Results in recombination and increased diversity
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Figure 2.8.
Mitosis
Meiosis I
Meiosis II
Metaphase
Metaphase I
Metaphase II
2N
N
2N
Metaphase Plate
Metaphase Plate
Metaphase Plate
Anaphase I
Anaphase II
Anaphase
Cytokinesis
Cytokinesis
Cytokinesis
N
N
N
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Meiosis
3
A
E
B
F
G
C
H
D
TETRAD
RAF
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Figure 2. 3.
Gregory Mendel working with peas made two
innovations to the science of genetics 1)
developed pure lines 2) counted his results and
kept statistical notes
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SOME MORE DEFINITIONS
Pure Line - a population that breeds true for a
particular trait this was an important
innovation because any non-pure (segregating)
generation would and did confuse the results of
genetic experiments Dominant - the allele that
expresses itself at the expense of an alternate
allele the phenotype that is expressed in the
F1 generation from the cross of two pure lines.
Recessive - an allele whose expression is
suppressed in the presence of a dominant allele
the phenotype that disappears in the F1
generation from the cross of two pure lines and
reappears in the F2 generation Co-dominance a
relationship among alleles where both alleles
contribute to the phenotype of the heterozygote.
Allele - one alternative form of a given
allelic pair tall and dwarf are the alleles for
the height of a pea plant more than two alleles
can exist for any specific gene, but only two of
them will be found within any individual
Allelic pair - the combination of two alleles
that comprise the gene pair
http//www.ndsu.edu/instruct/mcclean/plsc431/mende
l/mendel1.htm
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More Definitions !!!

• Homozygote - an individual which contains only
  one allele at the allelic pair for example DD is
  homozygous dominant and dd is homozygous
  recessive pure lines are homozygous for the gene
  of interest
• Heterozygote - an individual which contains one
  of each member of the gene pair for example the
  Dd heterozygote
• Genotype - the specific allelic combination for a
  certain gene or set of genes
• Phenotype - literally means "the form that is
  shown" it is the outward, physical appearance of
  a particular trait or traits determined by the
  genotype
• Mendel's pea plants exhibited the following
  phenotypes
• - round or wrinkled seed phenotype
• - yellow or green seed phenotype
• - red or white flower phenotype
• - tall or dwarf plant phenotype

http//www.ndsu.edu/instruct/mcclean/plsc431/mende
l/mendel1.htm
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Mendels Laws
Mendel's First Law - the law of segregation
during gamete formation each member of the
allelic pair separates from the other member to
form the genetic constitution of the gamete
Mendels Second Law -- the law of
independent assortment during gamete formation
the segregation of the alleles of one allelic
pair is independent of the segregation of the
alleles of another allelic pair
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Figure 2.5. Mendel's First Law - the law of
segregation during gamete formation each member
of the allelic pair separates from the other
member to form the genetic constitution of the
gamete
A. Monohybrid Cross
B. F1 Self Fertilization
Parent 1
Parent 2
Parent 2
Parent 1
X
X
Yy
YY
yy
Yy
Gametes
Y
Y
y
y
Gametes
Y
y
Y
y
F1 Fertilization
F2 Fertilization
YY Yy
Yy
F2 Plants 75 yellow 25 green
F1 Hybrid Plants 100 yellow
yy
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Figure 2.6. Independent Assortment Two or
more traits.
A. Dihybrid Cross
Parent 1
Parent 2
TTYY
X
ttyy
F1 Fertilization
TtYy
F1 Plants 100 tall/yellow
B. F1 Self Fertilization
TtYy
TtYy
X
Ratios of F2 Plants
F2 Fertilization
T_Y_ 9/16 tall/yellow
T_yy 3/16 tall/green
ttY_ 3/16 short/yellow
ttyy 1/16 short/green
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ty
ty
TY
TtYy
TtYy
TtYy
TtYy
TY
F1 Generation of Dihybid cross
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Figure 2.6. Independent Assortment Two or
more traits (color and height).
A. Dihybrid Cross
Parent 1
Parent 2
TTYY
X
ttyy
F1 Fertilization
TtYy
F1 Plants 100 tall/yellow
B. F1 Self Fertilization
TtYy
TtYy
X
Ratios of F2 Plants
F2 Fertilization
T_Y_ 9/16 tall/yellow
T_yy 3/16 tall/green
ttY_ 3/16 short/yellow
ttyy 1/16 short/green
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Co-dominance Variation to Mendel laws
Another Monohybrid Cross
RR Red Flower Parent -- rr White Flower
Parent
r
r
Rr
Rr
R
F1
R
Rr
Rr
If Dominance (R) then all should be RED
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F1
But co-dominance of R and r produces all pink
flowers
Rr
Rr
Rr
Rr
Rr x Rr
R
r
F2
Rr
RR
R
1 Red 2 Pink 1 White
r
rr
rR
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Flowers and Sexual Reproduction
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5
Flower Parts Only Angiosperms!
ST
PIST
SEP
PET
Figure 36.5. Morphology of a dicot flower. The
perfect flower of this Oxalis species has five
sepals (SEP), which are hidden from view in the
open flowers by the five petals (PET), five
stamens (ST) and one pistil (PIS). Compare to
Figures 36.5 and 36.6.
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4
ST
AN
ST
PIST
STL
FL
OVY
PET
OVL
SEP
REC
RAF
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STY
6
SEP
OVY
OVL
PET
LOC
OVL
OVL
FL
OVY
FIL
CAR
PET
SEP
REC
B
A
36
8
T
MMC
B
C
A
GN
S
PTN
PTN
PT
D
E
RAF
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7
A
V
I
MSMC
M
B
HN
N
C
DN
FMSN
D
AN
PN
E
S
M
RAF
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Youre Right!!! More Definitions
Self Incompatibility Plant that cannot
fertilize its female gametes with its own male
gametes. Basically two types Gametophytic in
which the pollen grain will not grow when it
shares the same incompatibility gene (s) and
Sporophytic in which the diploid parent hinders
germination and growth of the pollen tube. Both
types prevent double fertilization. Outcrossing
Species basically self-incompatible requires a
partner of a different genotype. Pollination
The process in which the pollen is carried from
the anther to the stigma. Basically two types
Cross (between different genotypes of plants) and
Self (same plant). Double Fertilization one
sperm nucleus unites with egg to form the zygote
and restore the sporophytic phase (2N) of the
plant and the other sperm nucleus fuses with the
polar nuclei of the female gametophyte to form
the primary endosperm nucleus (3N or greater).
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Figure 2.12
Gametophytic Incompatibility
Sporophytic Incompatibility
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Double Fertilization
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AN
PN
E
SP
PT
B
N
PG
PN
2
1
E
PT
PT
C
OVY
PEN
ZY
OVL
D
A
RAF
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Zygotic Embryo Ontogeny -- Dicot
Embryo
Suspensor
Bilateral Symmetry
Radial Symmetry
Figure 4.4
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YGE
I
EN
E
S
Zygotic embryogenesis Cercis canadensis (Eastern
Redbud)
A
A
D
GE
I
EN
S
C
B
C
SM
H
VT
RM
C
E
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Somatic Embryogenesis
EN
SC
CL
SM
Orchardgrass a monocot
SN
RM
CR
A
B
EN
C
I
SM
C
Eastern Redbud a dicot
H
SM
H
C
D