Chapter 12 Outline Introduction Asexual Sexual Reproduction The Phases of Meiosis Division I Division II Alternation of Generations Introduction Asexual Reproduction p roduction ID: 458986
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Slide1
Meiosis and Alternation of Generations
Chapter 12Slide2
Outline
Introduction
Asexual
Sexual Reproduction
The Phases of Meiosis
Division I
Division II
Alternation
of GenerationsSlide3
Introduction
Asexual
Reproduction
-
p
roduction
of cells identical in chromosomes with cells from which they arose
Sexual
Reproduction
-
i
n
nearly all plants
Results in formation of seeds in flowering and cone-bearing plants
Gametes
produced
Egg
and
sperm
unite to form
zygoteSlide4
Introduction
Asexual and Sexual ReproductionSlide5
Introduction
Cells
-> 2
sets of chromosomes,
1
set from each
parent
Members of each
chromosome pair identical
in:
Length
Amount of DNA
Genes carried
Location of
centromere
Homologous
Chromosomes
=
chromosome
pairsSlide6
Introduction
Results
of meiosis:
4
cells from
2
successive divisions
Cells with
half chromosome #
of
parents
Each cell rarely identical to original cell or each
otherSlide7
The Phases of Meiosis
Before meiosis, DNA molecules of each chromosome
double
Each chromosome has identical DNA molecules held together
by centromere
Meiosis:
Division I (Meiosis I or Reduction Division) -
#
of chromosomes reduced to
half
Division II (Meiosis II or
Equational
Division) -
no
further reduction in chromosome
#Slide8
The Phases of Meiosis
Division I
Prophase I
Chromosomes coil and condense, and
align
in homologous
pairs
Nuclear
envelope and nucleolus
disassociate
Each closely associated pair of chromosomes exchange parts =
crossing-over
Chromosomes coilSlide9
The Phases of Meiosis
Division I
Prophase I - Crossing-over
Chiasmata
form
Results in exchange of DNA by
2
parents
Chromosomes align in pairs; chiasmata visibleSlide10
The Phases of Meiosis
Division I
Metaphase I
Chromosomes align in pairs at
equator
Spindle formation
completedSlide11
The Phases of Meiosis
Division I
Anaphase I
One whole chromosome from each pair migrates to
pole
Telophase I
Original cell becomes
2 cells
or
2 nucleiSlide12
The Phases of Meiosis
Division II
Similar to mitosis
Prophase II
Chromosomes
become shorter and
thickerSlide13
The Phases of Meiosis
Division II
Similar to mitosis
Metaphase II
Centromeres become aligned along
equator
New spindles
completedSlide14
The Phases of Meiosis
Division II
Similar to mitosis
Anaphase II
Centromeres and chromatids of each chromosome separate, and migrate to opposite
polesSlide15
The Phases of Meiosis
Division II
Chromosomes at poles
Formation of cell walls
Telophase
II
Coils of chromatids relax and chromosomes become longer and
thinner
Nuclear envelope and nucleoli reappear for each group of
chromosomes
New cell walls
formSlide16
Alternation
of Generations
Haploid (1x) -
c
ell
with
1
set of chromosomes
Gametes
Diploid (2x) -
c
ell
with
2
sets of chromosomes
Zygote
Polyploid - cell with >2 sets of chromosomes
Triploid (3x) - 3 sets of chromosomes
Homologous chromosomes cannot pair properly, thus gametes typically inviableNavel oranges, seedless watermelonsTetraploid (4x) -
4
sets of chromosomes
Potatoes, pasta wheatSlide17
Alternation
of Generations
Alternation of
Generations
-
l
ife
cycle involving sexual
reproduction alternating
between
2
n
sporophyte phase and
1
n
gametophyte phaseSporophytes develop from zygotes and produce sporocytesSporocyte undergoes meiosis - produces 4 1n sporesSlide18
Alternation
of Generations
Gametophytes
develop from
spores
Form cells or sexual structures in which
gametes
are formed by mitosis
Fertilization produces
zygote
Fertilization
(
S
yngamy
)
=
fusion of gametesSlide19
Alternation
of Generations
First cell of gametophyte generation
= spore
, and last
cell = gamete
Any gametophyte cell
= 1
n
First cell of sporophyte generation
=
zygote, and last cell
=
sporocyte
Any
sporocyte
cell
= 2nSlide20
Alternation
of Generations
Change from sporophyte to gametophyte generation occurs
from meiosis
Change from gametophyte to sporophyte occurs
from fertilizationSlide21
Review
Introduction
Asexual
Sexual Reproduction
The Phases of Meiosis
Division I
Division II
Alternation
of Generations