LS10 Developmental biology review
Lesson 1 How is it possible that a complete
organism is generated from a single cell?
Preformism theory states: sperm cells are cells that
could caary the preformed offspring
★ So organisms develop from miniature
versions of themselves (homunculi)
★ It was believed that the form of living things
existed prior to their development
Epigenesis (William Harvey)
★ Showed that life came from eggs
★ Development through differentiation
Theory of recapitulation (Johann Friedrich Meckel)
★ The development of the embryo goes
through stages that represent evolution of ancestors
★ ‘’Ontogeny recapitulates phylogeny’’
★ Ontogeny = embryonic development represents
★ Phylogeny = history of evolution
★ Each species seems to recapitulate ancestral morphologies during its own development,
so they have common genetic developmental plans!
Development begins with a single cell-the fertilized egg/zygote (undifferentiated), which divides
mitotically to produce all the cells of the body into fully differentiated cells
★ Development does not stop at birth, or even at adulthood e.g. bone marrow generates
million of new red blood cells every minute, regeneration of severed parts,
metamorphosis etc.
★ Developmental biology is the discipline that studies embryonic development and other
processes related to organisms’ development
Cell polarization
★ Can happen due to external niche which keeps contact with one daughter cell =
extrinsic regulation
★ Only one daughter cell can maintain contact with the niche
★ Intrinsic regulation = regulators of self-renewal within a cell is localized asymmetrically
→ they are inherited by only one of the two daughter cells
, The two sides of a zygote differ → assymetrical
★ This happens after fertilization and determines the assymetry of the zygote
★ Myosin (in the cytoskeleton) rearranges to one side which determines the anterior and
posterior side
★ There are mechanisms which maintain the polarity before mitosis
PAR proteins: an internal cellular signal for
polarisation
★ PAR = partitioning defective genes
★ They are well conserved and create
domains which have a distinct
composition for different functions
★ A domain is created by proteins
interacting with each other and
aggregating
★ PAR proteins localize in a mutually exclusive matter → the loss of PAR proteins
(mutant) effects the localization on the other side
★ So posterior PARs are required to prevent anterior PAR proteins from lozaling at the
posterior side and vise versa!
Cellular polarization → asymmetric cell division
★ The anterior side is bigger than the posterior side
★ There is a relationship between PAR proteins and asymmetry in order for the two
daughter cells to dissociate
Lesson 1 How is it possible that a complete
organism is generated from a single cell?
Preformism theory states: sperm cells are cells that
could caary the preformed offspring
★ So organisms develop from miniature
versions of themselves (homunculi)
★ It was believed that the form of living things
existed prior to their development
Epigenesis (William Harvey)
★ Showed that life came from eggs
★ Development through differentiation
Theory of recapitulation (Johann Friedrich Meckel)
★ The development of the embryo goes
through stages that represent evolution of ancestors
★ ‘’Ontogeny recapitulates phylogeny’’
★ Ontogeny = embryonic development represents
★ Phylogeny = history of evolution
★ Each species seems to recapitulate ancestral morphologies during its own development,
so they have common genetic developmental plans!
Development begins with a single cell-the fertilized egg/zygote (undifferentiated), which divides
mitotically to produce all the cells of the body into fully differentiated cells
★ Development does not stop at birth, or even at adulthood e.g. bone marrow generates
million of new red blood cells every minute, regeneration of severed parts,
metamorphosis etc.
★ Developmental biology is the discipline that studies embryonic development and other
processes related to organisms’ development
Cell polarization
★ Can happen due to external niche which keeps contact with one daughter cell =
extrinsic regulation
★ Only one daughter cell can maintain contact with the niche
★ Intrinsic regulation = regulators of self-renewal within a cell is localized asymmetrically
→ they are inherited by only one of the two daughter cells
, The two sides of a zygote differ → assymetrical
★ This happens after fertilization and determines the assymetry of the zygote
★ Myosin (in the cytoskeleton) rearranges to one side which determines the anterior and
posterior side
★ There are mechanisms which maintain the polarity before mitosis
PAR proteins: an internal cellular signal for
polarisation
★ PAR = partitioning defective genes
★ They are well conserved and create
domains which have a distinct
composition for different functions
★ A domain is created by proteins
interacting with each other and
aggregating
★ PAR proteins localize in a mutually exclusive matter → the loss of PAR proteins
(mutant) effects the localization on the other side
★ So posterior PARs are required to prevent anterior PAR proteins from lozaling at the
posterior side and vise versa!
Cellular polarization → asymmetric cell division
★ The anterior side is bigger than the posterior side
★ There is a relationship between PAR proteins and asymmetry in order for the two
daughter cells to dissociate
