LESSON 2: THE
DEVELOPMENT OF ORGANISMS
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From previous lessons, you now have a
general idea of how cells communicate and change in embryos and
adult organisms. The next phase of understanding involves
putting these processes in the bigger picture of how cells work
together to form a functional individual. We will take a
chronological look at development starting with the early
stages, such as
fertilization and then move on to larger morphological changes
that occur later on in development. We will be using the typical
examples of plants and animals, but keep in mind that there are
a number of other multicellular eukaryotic organisms that have
similar processes and controls over development.
Understand the hierarchical
organization of developmental genes.
Become familiar with common
stages of early development.
Understand the factors
affecting the development of shape, or morphology, in
Topics covered in this Lesson
In previous topics and lessons we have
looked at how
genes are transcribed and
translated, but the question keeps coming up - how do cells and
organisms “know” what genes to transcribe when? Differential
gene expression during development has been studied in some
detail for a number of organisms. It turns out that development
often occurs as a cascade of events, with
proteins from one phase
regulating the activity of the genes of the next phase.
The pathways found in pattern formation
and organismal development can shed light on the evolutionary
history of very diverse organisms. As you work through the
details of segmentation and
homeobox genes in
organ identity genes in plants, keep in mind what these processes
are telling us about the way evolution works and how genetic
“solutions” are conserved.
- Understand the hierarchical arrangement
of regulatory cascades.
- Know what homeobox genes are and why they
are important in organismal development.
- Think about the similarities in the genes
controlling development in diverse organisms.
- Understand the process of organ identity
genes creating various plant structures.
As you have seen from previous lessons, multicellular organisms
begin as a single-celled zygote. The next few hours in the
development of an individual involve a series of dynamic and
critical processes such as
cleavage, and major morphological changes in the
embryo. Most cells are
by the end of these early stages, and the basic layout for the
organism has been made. Keep in mind through this lesson the
similarities of developmental processes and reflect back on the
regulatory cascades from the previous module.
Know which stage of development
represents the first incidence of cell signaling processes
What are some of the key
differences in the development of animals versus plants?
How are the developmental processes
in animals and plants similar?
Understand what processes cause
morphological changes in the developing embryo.
Develop an understanding of how a
zygote becomes a late-stage embryo in both plants and
have explored the early stages of development in multicellular
organisms. But we know that development does not end there.
Pattern formation and morphogenesis are processes that “sculpt”
and refine the late-stage embryo into a fully-functional
organism. As we will see in this module, developmental changes
don’t stop here either. In fact,
phenotypic changes occur throughout the lifetime of most
organisms. Sometimes these changes are drastic, such as the
regeneration of a limb, and some are more subtle but equally
important, like seasonal color change.
- Understand how cell induction and
morphogens give cells in the developing embryo
positional information that leads to the formation of
- What role does apoptosis play in the
formation of organisms?
- Know the difference between
dedifferentiated and undifferentiated cells and how each
of them plays a role in pattern formation.
- What is phenotypic plasticity, and
how does it relate to changes in adult organisms?