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Development
Including Mitosis and
Meiosis
A. Russo-Neustadt
CSULA
Lancelet early development
I. The Cell Cycle
Division of cytoplasm
and organelles between
new cells
G = gap
IPMAT
M = mitosis or
meiosis, DNA is
divided between
two new cells
Regular sequence of events in which a cell grows and carries
out regular activities, prepares to divide and then divides to
produce two new cells
II. Comparison of Mitosis and
Meiosis
Mitosis
A. Results in 2 new
cells with the same #
of chromosomes as
the original cell
2n = diploid cell
Meiosis
A. Results in 4 new
cells each with ½ the
# of chromosomes as
the original cell
2n cell
2 X 2n cells
4 X 1n = haploid
cells
II. Comparison of Mitosis and
Meiosis - continued
Mitosis
B. Cytokinesis is usually
approximately equal
C. Used for –
growth
repair
development
(embryogenesis)
asexual reproduction
Meiosis
B. Cytokinesis can be
unequal (oogenesis)
C. Used for –
gametogenesis
Definitions
Homologous
chromosomes =
chromosomes that
contain information
to control the same
genetic trait, one
member of each pair
came from mom and
one came from dad
Chromosome = DNA and its
associated proteins, 46 in humans
Definitions – continued:
Site where sister chromatids
are held together,
microtubules of spindle
apparatus attach here during
cell division
Copies of the same chromosome that
result from S phase
Definitions – continued:
Equator = center
plane of the cell
Spindle apparatus = portion of the cytoskeleton that
orients and separates sister chromatids or homologous
chromosomes during cell division; contains poles and
microtubules
How is Diversity achieved?
CROSSING OVER
INDEPENDENT ASSORTMENT
LET’S REVIEW
if time permits
Steps in Development
A.
Gametogenesis = production of
gametes through the process of meiosis
1.
Spermatogenesis = sperm cell production
2 meiotic divisions
2n
1n
1n
1n
1n
2n (diploid) testis cell
4 X 1n (haploid) sperm cells
A. Gametogenesis - continued
B. Oogenesis = egg cell production
2 meiotic divisions
1n
2n
1n
1n
2n (diploid) follicle cell
1n
1 haploid (1n) egg + 3 haploid
polar bodies
Gets all the
cytoplasm and
organelles at
cytokinesis
essentially 3
haploid nuclei that
are discarded
B. Fertilization
The union of an egg cell and a sperm cell
that produces a zygote (fertile egg)
and re-establishes the diploid
condition
fusion
1n
2n
egg
zygote
1n
sperm
C. Embryogenesis
embryo formation: consists of cleavage +
gastrulation + organ formation
All three steps will make use of mitosis to
produce new cells
1. Cleavage = division
of the single celled
zygote into a many
celled structure called
a blastula (hollow ball
of cells); uses mitosis
so that all cells in the
developing animal will
have a complete set of
genes
Fluid-filled
2n
X.S.
Requires multiple mitotic divisions
2n
2n
2n
2n
2. Gastrulation = transformation
using complex cell movements
of a blastula into a multi-layered
animal (gastrula); mitotic cell
division continues as developing
animal continues to increase in
size
Breaks
through to
form
mouth or
anus
l.s.
gut
becomes mouth or anus
x.s.
gut
All cells are 2n
3. Organ Formation
Differentiation and specialization of
embryonic tissues (endoderm, ectoderm
and mesoderm) into adult tissues
(epithelial, connective, muscle and
nervous tissues) and organs
Final Steps in Development
D. Growth = increase in size; differentiation
usually continues
E. Maturation = attainment of adult body
form capable of reproduction
metamorphosis as an example of a
dramatic maturation process