Download Reproduction

Organismal Development
Part 1
Prokaryotes and Protists
Important concepts from previous units:
• Cells that divide by mitosis produce
genetically identical offspring.
• Cells divide when they become inefficient at
transport across the cell membrane.
• Cells that reproduce sexually depend on
cell-to-cell communication/contact.
• All matter and energy for growth and
development comes from the environment.
Modes (ways of doing) of
reproduction
• Asexually – Basically, the making of genetically
identical clones. No exchange of DNA occurs.
• Sexually – The fusion of two different gametes
(sperm and egg) to create a Zygote (fertilized egg)
that has variation.
– Remember, variation is the key to survival in changing
environments.
– To create sperm and eggs, certain diploid cells
have to undergo meiosis, which involves two
divisions of chromosomes to become haploid
cells.
Sexual Reproduction
Types of Asexual Reproduction:
• Binary Fission – term for Bacterial reproduction
• Budding – organisms, such as polyps (sessile form of
jellyfish), are generating genetically identical “buds”
that break off to become a new organism.
• Fragmentation and regeneration - Seen in the
Platyhelminthes (flatworms) and Echinoderms
(starfish).
– For example, a single arm of a starfish gets removed. The
starfish will grow (regenerate) a new arm in that same
place. The removed arm will (fragment) will become a new
starfish.
Asexual - Budding
Platyhelminthes - Regeneration
Binary Fission
• This is the process of Reproduction/Replication in prokaryotes
(bacteria).
– DNA replication(S phase) starts at the “origin” and works
around the entire single, circular chromosome, this results in
two identical chromosomes in the nucleoid region.
– This is followed by producing a cleavage furrow (cytokinesis)
to produce 2 new cells that are referred to as clones.
• The cleavage furrow is produced using actin and myosin
microfilaments.
• How is Binary Fission related to mitosis in terms of evolution?
– Binary Fission would have evolved into Mitosis as the DNA
content increased dramatically and also the endosymbiant
hypothesis occurred to produce “organelles”. The two major
steps are the same: synthesis and division.
– 100% genetically identical clones are produced by this
process.
Cell wall
Origin of
replication
Asexual – Binary
Fission
E. coli cell
Chromosome replication
begins.
Soon thereafter,
one copy of the origin
moves rapidly toward the
other end of the cell.
Replication continues. One
copy of the origin is now at
each end of the cell.
Replication finishes.
The plasma membrane
grows inward, and
new cell wall is deposited.
Two daughter
cells result.
Two copies
of origin
Origin
Plasma
membrane
Bacterial
chromosome
Origin
Bacterial Variation Processes
• Remember, variation increases survival chances
within a changing environment.
• Transformation (This is a simple change of DNA
content.)
– A bacteria took in DNA from an external source.
Recombination of DNA occurred. Variation “created”.
– Biotechnology? This is what we do, in laboratories, to
make bacteria “learn” new tricks.
Transformation
• Transduction (This is
when new DNA has been
carried in by a virus thus
creating the “change”.
– A phage (virus) introduced
the new DNA into the
bacterial. The two DNAs
combined into one
genome.
– Bacteria exchange plasmids (small circular pieces
of DNA) through a conjugation tube from the
“male” to the “female” (Bacteria DO NOT have
sexes like humans do.)
– F factor (If a bacteria possess this gene, they are
considered “male”.) (Shown as F+); (F- are
“female”.)(They do NOT possess the F factor
gene.)
– Pili – This structure is a “sex whip” for pulling the
“female” close so that a conjugation tube can be
made between the two bacteria. The pili is
created by expressing the F factor gene.
Conjugation in Bacteria
Sex pilus
5 µm
PROTISTS
(These are mostly single celled organisms.)
• Reproductive Means
– Some are sexually reproducing organisms.
• Remember, this method favors variety.
• The organism makes haploid gamete structures
through the process of meiosis.
• The gametes are released from the parent organism.
• The male and female gametes combine to form a
genetically new diploid zygote.
• The zygote develops over time into the “adult”
organism.
PROTISTS
• Some are asexual reproducing organisms.
– This is a faster process but produces no variation;
they are all clones.
– Essentially, it is a process just like Binary Fission,
except
• they have a nucleus with linear chromosomes and
organelles in the cytoplasm;
• so therefore, there is a G2 phase and it is followed by
Mitosis and Cytokinesis. (We call this whole process
Mitosis. Just like we discussed with the Cell cycle)
Cell Cycle with checkpoints
(Is all going according to plan?)
G2 followed by Mitosis
Mitosis continued followed by
cytokinesis
Important concepts from previous
units:
• Haploid refers to having one half the DNA content of
a normal Diploid cell. We represent it as “n”.
• Diploid refers to having two halves (a whole) of the
normal DNA content. We represent it as “2n”.
• S phase replicates the DNA of a cell. Mitosis has one
division of DNA. Meiosis has 2 divisions of DNA.
FUNGUS
Fungal Life Cycles
• Majority of the life is spent as haploid asexual
organisms.
– This allows the organism to reproduce much
faster and colonize a dead organism for food
and reduce competition with other organisms.
– Haploid spores can be produced by mitosis and
then released to reproduce, in favorable
environments, very quickly.
Germ tube (Growing Spore)
(initial hypha)
single hypha
Mass of hyphae (mycelium)
• Fungi use the diploid state to create variation.
(Remember, variation helps with survival in a
changing environment.
– All sexual reproduction, for all types of fungus,
involves three phases:
– Plasmogamy - This is the fusion of cytoplasms.
(+=male; - =female) The “female” is signaled by the
release of pheromones from the “male”.
• This fusion together of hyphae results in
heterokaryon (Means “different nuclei”) or
Dikaryotic (Means “two nuclei”).
– Karyogamy – This is the fusion of nuclei. This makes
the hyphae now 2n (Diploid) in genetic content.
(VARIATION)
– Meiosis of the diploid (2n) zygote to return to a
haploid (n) state. Variation has been “created”.
PLANTS
• Sexual Reproduction in plants using Alternation of
Generations
– Sporophyte (2n) This generation produces diploid spores
that undergo meiosis to become haploid (n) spores.
• The haploid spores are released (in the case of the seedless
plants) into the environment or retained in the case of
gymnosperms and angiosperms (the seed producing plants).
• Released spores hopefully will find a suitable environment to
grow and produce gametophyte.
• Retained spores will develop into a single celled gametophyte,
the sperm or egg.
– The haploid gametophyte (n) produces haploid gametes
that are released if male and retained if female.
• The male gamete, sperm, travels to the female gamete, egg, to
fertilize and form a diploid zygote.
• The diploid zygote will grow into the new sporophyte
generaration.
•
Asexual reproduction methods in plants (A.K.A.
Vegetative Reproduction or Vegetative propagation)
– Fragmentation – A piece of the original plant breaks off
and lands implants the cut edge in the dirt.
• This fragment of cells begin to develop missing parts so long
as Xylem tissue runs in right direction… up.
– Cuttings – “Man” removes a piece and puts in water or soil
to grow. (Like fragmentation; but caused by “man”.)
– Grafting – This is the combining of two different plants.
• Stock – This is the part with established roots.
• Scion – This is the cutting to be attached to the stock plant.
– Tissue Cultures – This uses plant cells to make clones.
• These cells are said to be totipotential (means “they can
make all types of cells”).
Apoptosis
• This is the “programmed” cell death of cells
to create important anatomical structures.
– It is controlled by DNA genes within the cells of
developing organisms.
– An example would be the death and hollowing out
of cells to create the water moving xylem tissue of
plants.