Mendelian Genetics, Plant Sexual Reproduction and Other Stuff
R. N. Trigiano, Professor EPP
17 January 2012
Alternation of Generations
Mitosis and Meiosis
Mendelian Genetics
Sexual Reproduction in Plants
ALTERNATION OF GENERATIONS
DEFINITIONS:
Diploid: Having two sets of chromomosomes 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 = X=11 (Flowering dogwood)
Polyploid: Having more than two sets of chromosomes – 2N = 6X = 54 sporophyte; gametophyte N = 3X= 27 (Chrysanthemum)
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 Spores (n)
SHADED AREA REPRESENT RELATIVE TIME IN DIPLOID OR
SPOROPHYTIC PHASE; OPEN = RELATIVE TIME IN HAPLOID
OR GAMETOPHYTIC PHASE.
ALTERNATION OF GENERATIONS
Lower Plants Higher Plants
A
1
B
CD
E
MOSS FERN
A
B
C
Dwww.calflora.net
silviahartmann.com
Mitosis and Meiosis
http://www.phschool.com/science/biology_place/biocoach/index.html
http://www.vcbio.science.ru.nl/images/cellcycle/mmitosis_onion_zoom.jpg
Figure 6.1
Structure of DNA
Nitrogenous bases
AdenineThymineGuanineCytosine
Phosphate (PO4)
Deoxyribose sugar
Chromatid Sister Chromatids
DNA Synthesis
Chromosome 1 Chromosome 1
Centromere Centromere
B. Chromosome Conformations C. Homologous Chromosomes
Chromosome 1 Chromosome 2
Locus 1
Locus 2
Condensed ChromosomeRelaxed Chromosome
A. Chromosome Physical States
Nucleus Nucleus
Figure 2.2
http://nobelprize.org/nobel_prizes/medicine/laureates/2001/cellcycle_eng.jpg
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.
http://tainano.com/Molecular%20Biology%20Glossary.files/image011.gif
http://www.vcbio.science.ru.nl/images/cellcycle/mmitosis_onion_zoom.jpg
1 = Interphase, 2-5 = Prophase; 6 = Early Metaphase; 7 = Late Metaphase; 8 = Anaphase; 9 = Telophase; 10 = Completion of Cytokinesis
Interphase
Figure 2.7. Mitosis
Nucleus
ProphaseMetaphase
Telophase
Anaphase
Cytokinesis
Metaphase Plate
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.
Stages of Meiosis
Prophase: 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 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.
A. B. C.
Figure 2.9. Crossing- over
Chiasma - Exchange between homologous chromosomes. Actually sister chromatids during Prophase I.
Results in recombination and increased diversity
Synapse – pairing of homologous Chromosomes
Mitosis Meiosis I Meiosis IIMetaphase Metaphase I Metaphase II
AnaphaseAnaphase I Anaphase II
Cytokinesis Cytokinesis Cytokinesis
Metaphase PlateMetaphase PlateMetaphase Plate
Figure 2.8.
2N
N
2N
N
N
N
A
B
C
D
E
F
G
H
RAF
3 Meiosis
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
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]
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
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.
Allelic pair - the combination of two alleles that comprise the gene pair
SOME MORE DEFINITIONS
http://www.ndsu.edu/instruct/mcclean/plsc431/mendel/mendel1.htm
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
• 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/mendel/mendel1.htm
Mendel's First Law - the law of segregation; during gameteformation each member of the allelic pair separates from the other member to form the genetic constitution of the gamete
e.g. A a yields gametes with A a
Mendel’s 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
Mendel’s Laws
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
Parent 1 Parent 2
YY yy
X
Yy Yy
YyYy
y
y
Y Y
Parent 1
Parent 2
F1 Hybrid Plants: 100% yellow
Parent 1 Parent 2
Yy Yy
X
YY Yy
yyYy
Y
Y
Y y
Parent 1
Parent 2
F2 Plants: 75% yellow 25% green
A. Monohybrid Cross
Gametes: Y Y y y Gametes: Y y Y y
Yy
B. F1 Self Fertilization
YY & Yy
yy
F1 Fertilization: F2 Fertilization:
TtYy
TTYY TTYy
TY
Parent 1
Parent 2
TtYY TtYy
Ty tY ty
TTYy TTyy TtYy Ttyy
TyYY TtYy ttYY ttYy
TtYy Ttyy ttYy ttyy
TY
Ty
tY
ty
Figure 2.6. Independent Assortment – Two or more traits.
TtYy
TTYY ttyy
F2 Fertilization:
T_Y_ = 9/16tall/yellow
T_yy = 3/16tall/green
ttY_ = 3/16short/yellow
ttyy = 1/16short/green
F1 Fertilization:
X
F1 Plants: 100% tall/yellow
TtYy
X
Ratios ofF2 Plants:
Parent 1 Parent 2
B. F1 Self Fertilization
A. Dihybrid Cross
TY
TY
ty ty
TtYy
TtYy
TtYy
TtYy
F1 Generation of Dihybid cross
TtYy
TTYY TTYy
TY
Parent 1
Parent 2
TtYY TtYy
Ty tY ty
TTYy TTyy TtYy Ttyy
TyYY TtYy ttYY ttYy
TtYy Ttyy ttYy ttyy
TY
Ty
tY
ty
Figure 2.6. Independent Assortment – Two or more traits (color and height).
TtYy
TTYY ttyy
F2 Fertilization:
T_Y_ = 9/16tall/yellow
T_yy = 3/16tall/green
ttY_ = 3/16short/yellow
ttyy = 1/16short/green
F1 Fertilization:
X
F1 Plants: 100% tall/yellow
TtYy
X
Ratios ofF2 Plants:
Parent 1 Parent 2
B. F1 Self Fertilization
A. Dihybrid Cross
Co-dominance –Variation to Mendel “laws”
Another Monohybrid Cross
RR = Red Flower Parent -- rr = White Flower Parent
R
R
r r
Rr Rr
Rr Rr
If Dominance (R) then all should be RED
F1
Rr Rr
Rr Rr
But co-dominance of R and rproduces all pink flowers
R
R
r
r
RR
rR
Rr
rr
1 Red; 2 Pink; 1 WhiteF2
Flowers and Sexual Reproduction
ST
PET
SEP
PIST
5
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.
Flower Parts – Only Angiosperms!
SEP
PET
REC
AN
STFL
ST
STL
OVY
PIST
OVL
RAF
4
OVL
OVY FL
PET
SEP
OVL
OVY
REC
STY
FILPETSEP
A B
CAR
LOCOVL
6
A
B C
D E
MMC
GN
PTNS
PTN
PT
T
RAF
8
IV
MSMC
A
B
FMSN
DN
N
C
AN
PN
M
E
HN
D
SM RAF
7
You’re 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 uniting with the polar nuclei of the female gametophyte to form the primary endosperm nucleus.
Figure 2.12 Pollen parent genotypeS1S2
S1 S2 S1 S2 S1 S2
Pollen parent genotypeS1S2
S1 S3 S1 S3 S1 S3
S1S2 pistil
ES ES ES
ESESES
S1S2 pistil
S1S3 pistil
(a)
(b)
S2S3 pistil
S3S4 pistil
S2S4 pistil
Gametophytic Incompatibility
Sporophytic Incompatibility
B
C
D
PT
PN
SPE
12
PEN
ZY
PG
PT
OVY
OVL
A
PT
AN
N
E
PN
RAF
9 Double Fertilization
Figure 4.4
Zygotic Embryo Ontogeny -- Dicot
AA
YGE
S
EN
B
GE
S
C
I
D
VT
C
I
EN
C
SMH
RM
E
E
10
Zygotic embryogenesisCercis canadensis(Eastern Redbud)
A B
C D
SC
CL
EN
SM
RM
CR
SN
H
H
EN
SM
SMC
CI
11 Somatic Embryogenesis
Orchardgrass – a monocot
Eastern Redbud – a dicot