MEKANISME SEL DAN SIKLUS
HIDUP TANAMAN
MITOSIS
-
-
Istilah mitosis : proses yg menghasilkan dua sel
anak yg identik.
Mitosis memegang peranan dalam pertumbuhan
dan perkembangan organisme.
Pada tanaman mitosis terjadi pd sel-sel
meristematis, misalnya kambium, ujung-ujung akar,
dan ujung batang.
Mitosis
Prophase
• In prophase, the cell begins the process of
division.
• 1. The chromosomes condense. The
proteins attached to the DNA cause the
chromosomes to go from long thin structures
to short fat one, which makes them easier to
pull apart.
• 2. The nuclear envelope disappears. The
double membrane that surround the nucleus
dissolves into a collection of small vesicles,
freeing the chromosomes to use the whole
cell for division
• 3. The centrosomes move to opposite poles.
During interphase, the pair of centrosomes
were together just outside the nucleus. In
prophase they separate and move to
opposite ends of the cell.
• 4. The spindle starts to form, growing out of
the centrosomes towards the chromosomes.
Metaphase
• Metaphase is a short resting
period where the
chromosomes are lined up on
the equator of the cell, with
the centrosomes at opposite
ends and the spindle fibers
attached to the centromeres.
Everything is aligned for the
rest of the division process to
occur.
Anaphase
• In anaphase, the centromeres
divide. At this point, each
individual chromosome goes
from:
– 1 chromosome with 2
chromatids
– to: 2 chromosomes with one
chromatid each.
• Then the spindle fibers
contract, and the
chromosomes are pulled to
opposite poles, towards the
centrosomes.
Telophase
• In telophase the cell
actually divides.
• The chromosomes are at
the poles of the spindle.
• The spindle disintegrates
• The nuclear envelope reforms around the two sets
of chromosomes.
• The cytoplasm is divided
into 2 separate cells, the
process of cytokinesis.
Cytokinesis
• The organelles (other than the
chromosomes) get divided up into
the 2 daughter cells passively:
they go with whichever cell they
find themselves in.
• Plant and animal cells divide the
cytoplasm in different ways.
• In plant cells, a new cell wall made
of cellulose forms between the 2
new nuclei, about where the
chromosomes lined up in
metaphase. Cell membranes form
along the surfaces of this wall.
When the new wall joins with the
existing side wall, the 2 cells have
become separate.
• In animal cells, a ring of actin
fibers (microfilaments are
composed of actin) forms around
the cell equator and contacts,
pinching the cell in half.
Meiosis
• Different from somatic cell
• Reduces the number of chromosomes in new
cells to half the number in the original cell
• Produces gametes (sperm and egg cells)
Terjadi 4 kejadian penting pd meiosis
• Perpasangan kromosom yg homolog
(synapsis)
• Pertukaran bag kromosom (crossing over)
• Distribusi kembali kromosom
• Susunan materi genetik mungkin berbeda dg
tetua akibat crossing over
Gamete Formation
• Gametes are sex cells (sperm, eggs)
• Arise from germ cells
ovaries
testes
anther
ovary
Stages of Meiosis
Meiosis I
Meiosis II
• Prophase I
• Prophase II
• Metaphase I
• Metaphase II
• Anaphase I
• Anaphase II
• Telophase I
• Telophase II
Mitosis Vs meiosis
DNA Replication
Meiosis
Meiosis I
Each homologue in the
cell pairs with its partner,
then the partners
separate
Meiosis I - Stages
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase I
• Each duplicated, condensed chromosome
pairs with its homologue (synapsis)
• Homologues swap segments (crossing over)
Homologous Chromosomes
Homologous Chromosomes
Synapsis
Crossing
Over
Effect of Crossing Over
• After crossing over, each chromosome
contains both maternal and parental
segments
• Creates new allele combinations in offspring
Metaphase I
• Chromosomes are pushed and pulled into the
middle of cell
• Sister chromatids of one homologue orient
toward one pole, and those of other
homologue toward opposite pole
Anaphase I
• Homologous chromosomes segregate from
each other randomly (independent
assortment)
• Independent assortment results in genetic
variation
Independent Assortment
Telophase I and Cytokinesis
• The chromosomes arrive at opposite poles
• The cytoplasm divides
• There are now two haploid cells
• This completes Meiosis I
Meiosis II
• The two sister chromatids of each duplicated
chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
Meiosis II - Stages
Prophase II
Metaphase II
Anaphase II
Telophase II
Prophase II
• Microtubules attach to the kinetochores of
the duplicated chromosomes
• Chromosomes move toward the spindle’s
equator
Metaphase II
• All of the duplicated chromosomes are
lined up at the spindle equator, midway
between the poles
Anaphase II
• Sister chromatids separate to become
independent chromosomes and move to
opposite poles
Telophase II and Cytokinesis
• The chromosomes arrive at opposite ends of
the cell
• A nuclear envelope forms around each set of
chromosomes
• The cytoplasm divides
• There are now four haploid cells
Meiosis Animation I
Meiosis Animation II
Results of Mitosis and Meiosis
• Mitosis
– Two diploid cells produced
– Each identical to parent
• Meiosis
– Four haploid cells produced
– Differ from parent and one another
SIKLUS HIDUP TANAMAN
Gametogenesis Tumbuhan
• Mikrosporogenesis (pd anther)
• Megasporogenesis (pd bunga betina/ovarium)
Canna
Hibiscus
Microsporogenesis
Megasporogenesis
Megasporogenesis & Megagametogenesis
Megasporogenesis & Megagametogenesis
Megasporogenesis & Megagametogenesis