Ch. 12: mitosis, Meiosis, and life cycles
How does a plant grow?
• Cell cycle
– Activities of a cell from one cell division to
the next
What is a chromosome?
• =
•
•
•
•
•
•
Cabbage: 18
Cotton: 52
Mango: 40
Corn: 20
Foxglove: 56
Oak tree:24
Fig 8.7
The Events of the Interphase
• Interphase:
–
Divided into 3 phases:
G1 –
S–
G2 – cell growth after DNA replication; cell
prepares to divide
Cell Division or “M” phase
• Cell Division consists of two parts
1. Mitosis:
2. Cytokinesis:
• What needs to happen to the chromosomes prior to
Mitosis?
• During mitosis?
Fig 8.6
Sketch of one duplicated chromosome
Each chromatid has one
DNA molecule
1.
2.
How do
sister
chromatids
compare
genetically?
What
happens to
sister
chromatids
during
mitosis?
Sister chromatids
Centromere
Mitosis: sister chromatids separate
Two-chromatid
chromosome
One-chromatid
chromosome
One-chromatid
chromosome
S-Phase: DNA Replication
Interphase
The number
of
chromosomes
in each
daughter cell
is the same as
the number of
chromosomes
in the parent
cell
Mitosis: Division of the Nucleus
Four Stages:
1. Prophase –
1. .
2. .
3. Chromosomes attach to spindle fibers
2. Metaphase – Spindle fibers align the chromosomes at the
equator of the cell
3. Anaphase –
4. Telophase – nuclear envelope forms around each cluster
of chromosomes
Fig 8.8
Cytokinesis: division of the cytoplasm to
create 2 new cells
Fig 8.9
• Mitosis
• Meiosis
– A reductive division (46 C  23 C)
– Daughter cells are genetically different
• Karyotype =
• How many pairs of
chromosomes in this
Karyotype?
• Paired chromosomes are
homologous =
Normal Karyotype
of Human
Chromosomes
Diploid cell: 3 sets of
homologous
chromosomes
Haploid cell
One set of
non-homologous
chromosomes
Haploid cell
One set of nonhomologous
chromosomes
• Diploid cell –
• Haploid cell – contains only ONE
chromosome of each pair (n)
Meiosis
• Only occurs within the male and female
sporangium (all other cell divisions are
mitosis)
Fig 8.15
Fig 8.16 Meiosis I
Stages of Meoisis
1. Interphase – same as mitosis (G1, S, G2)
2. Meiosis I
a) Prophase I –
b) Metaphase I –
c) Anaphase I –
d) Telophase I –
3. Meiosis II
a) Prophase II – chromosomes attach to spindle
b) Metaphase II – chromosomes align at equator
c) Anaphase II – sister chromatids separate
d) Telophase II – cells divide, end result = 4 haploid
daughter cells
Plant sexual life cycles: Alternation of Generations
•
2 multicellular life stages:
1. Sporophyte:
• Spores – haploid cells that can grow into a
new, multicellular, haploid organism (the
gametophyte) without fusing to another cell.
2. Gametophyte:
•
Egg & sperm fuse to form the diploid zygote,
which divides by mitosis to form the sporophyte