GENETICS & DEVELOPMENT - Cell Division
Physical Basis of Inheritability... Key Concepts*
Mechanisms of Cell Reproduction... egg & sperm cells
cells reproduce identically, yet w variation (new traits)
"All living cells arise from pre-existing cells"
GENETICS asks.... HOW? mechanisms at cellular & molecular level
DEVELOPMENT looks.... at the LIFE CYCLE of organisms
1. reproduction mechanisms of organisms
2. growth of organism..... zygote to adult
cell differentiation - how one cell becomes different from another
differential gene activity - genes are active at different times
totipotency & cloning - exact genetic copies
METHODS of CELL REPRODUCTION
include...
Fission*
- binary = 2 equal halves (bacteria
& cyanobacteria &
protozoans)
Budding* - outgrowths detach = new organism (unequal)
(hydra)
Chapter 46.1 video:
Video: Hydra Budding
Mitosis* - asexually = identical
genetic copies [cytokinesis*]
genetically equal somatic cells
c7 fig 1.5 lung
cell*
amoeba, bone, marrow, & fertilized egg cell
divisions
Meiosis* - sexually produces sperm & egg cells with
1/2
chromosome # & new gene combos
Mitosis
- Asexual Reproduction Cell Cycle...
results in copying & equal duplication of
parental cell's DNA
and the equal division of chromosomes
into two daughter cells
(rates =
liver cells 1x/yr
- epithelial cells
1x/day)
the Life cycle of a
Cell... is referred to as the "CELL
CYCLE"...
Concept Activity
12.2 -
The Cell Cycle
[3 Stages] -
Cell Cycle
is depicted as a circle
360o
fig
12.5*
[G1 -
S -
G2 -
M]
Interphase
- period between successive divisions of a cell
3 parts
= G1 -
before, DNA synthesis (S), &
G2 period after
MITOSIS
- nuclear division phase; separation & duplication of chromosomes
Cytokenesis*
- physical
division of cell into two parts:
animals/plants
Names and
Numbers - (to protect the innocent)
bacteria have about 3,000 genes & 1 chromosome
humans have some 20 to 25,000+ genes & 46 chromosomes
Humans have 46 chromosomes
or 23 HOMOLOGOUS pairs
23 maternal chromosomes
23 paternal chromosomes
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Control of Cell Division and the Cell Cycle
2001 Nobel prize
Regulated by "Growth Factors" -
proteins that promote cell division
|
MPF -
mitotic promoting factor... [
complex* of
two proteins cdk + cyclin]
MPF is a kinase
enzyme, ones that switches on/off target cell
cycle
proteins by phosphorylating them.....
inactive cycle protein ----------------> active-P
ATP ---> ADP |
MPF promotes entrance into
mitosis from the G2 phase by
phosphorylating
multiple
proteins during mitosis including one that leads to destruction of
cyclin itself
MPF - cdk - a
cell division control protein - cyclin dependent kinase;
active only when bound to
cyclin;
cyclin - a
protein whose amount
varies cyclically*;
when in
high concentrations*, binds to
cdk makes MPF...
[cyclin + cdk =
MPF]... favors
Mitosis
|
 |
Growth Factors
regulate at critical points...
Cell
cycle checkpoints*
|
| Concept Activity -
12.1 -
Roles of Cell Division |
SEXUAL CELL
REPRODUCTION...
"MEIOSIS"
compare
physical
differences*
between nuclear division of MEIOSIS & MITOSIS
so the Distinct
Differences are:
Key Concepts*
meiosis
= 4 progeny cells [1 = 2 = 4]...
thus
2 divisions
mitosis
= 2 daughter cells only...
thus 1 cell division
meiosis = one-half number of chromosomes
mitosis
= same # of chromosomes as parent cell
meiosis = new combinations of gene not
in parents &
chromosomes sort randomly
of each other
mitosis
= daughter cells are genetically identical
Sexual Cell Reproduction
(Meiosis)
Where does meiosis occur during sexual cell cycle ?
Meiosis ---> produces cells
half chrm # =
23 (sperm & egg
- haploid)
fertilization (sperm + egg) ----->
diploid life cycle*
(chrm # =
46)
Alternation
of Generations*
& Human
life Cycle
Concept Activity 13.1 -
Asexual and Sexual Life Cycles
Stages of Sexual Cell Division
same 3 phases... just as in asexual division
(Interphase,
Nuclear Division,
Cytokinesis)
but,
2 Divisions Meiosis I and
Meiosis II
1 cell = 2 cell = 4 cells
Names of stages are same & have analogous functions
Meiosis
I...
Prophase I = chromosomes condense
SYNAPSIS -
homologs PAIR together = tetrad
CROSSOVER*
- exchange at
chiasma*
Metaphase I = chromosomes align at equator
Anaphase I = chromosomes migrate toward poles
Telophase I = chromosome at poles - cell domains separate
Meiosis I
separates homologs of homologous pair*
fig 13.7*
Meiosis II... is just like mitosis
separates chromatids of
one homolog of the homologous pair
just as is done in mitosis
Comparison(fig
13.9)*
of Mitosis/Meiosis -
comparison animation
Independent Assortment* - random alignment homologs
(fig)
Crossing Over - exchange of chromosome material
Concept Activity 13.3 -
Meiosis Animation
Sumanas, Inc. animation of Meiosis*
|
Summary of MEIOSIS
[table
of differences]* |
| 1.
Nuclear division phase of sexual cell reproduction |
2. Two successive divisions, results in 4 daughter cells...
Meiosis 1 and Meiosis 2 |
3. Reduction/division occurs....
diploid ---->
haploid
daughter cells ½
number of parent cell chromosomes |
4. Stages have same nomenclature as Mitosis
prophase, metaphase,
anaphase, telophase,
M1 &
M2 |
5. Only one S phase, where DNA is duplicated
often may be no interphase between
M1 &
M2 |
6. Homologs separate in Meiosis 1
Chromatids separate in Meiosis 2 (mitotic-like) |
7. Random Assortment occurs...... homologs align
at equitorial plates
independent of each other |
8. Crossing
over... may occur in Prophase I...
synapsis = close pairing homologs allows exchange
chiasma = point exchange of sister chromatids
|
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Consequences of sex...
new gene/chromosome combos
that did not exist in either parent,
which will become
the stuff of evolution...
next lecture
 Key Concepts*
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