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Premedical Biology
Individual development in
Different types of cells have the same genetic
information, create different proteins as result of
regulatin of transcription.
Tissue specific proteins / determinated
[differentiated] cells
Maternal molecules in cytoplasm and local cell
signalling regulate transcription
General principles have being studied on model
Model organisms
melanogaster - fruit fly
Xenopus laevis - frog
elegans – nematode
Mus musculus
Zygote / embryonal development means
cell division, cell differentiation and morphogenesis/
create a form
genetic information for many types of cells, for
threedimensional form / morfogenetic movements
1. Maternal determinants in egg:
protein molecules, RNA, mRNA….= cytoplasmatic
imformation molecules
Cytoplasmatic determinants
2. Signal molecules/ induction
are coded of offspring genome,
Process is accomplished by chemical signals –
have target cells / local signalling
and cell surface interactions
- responsible of early diferentiation, early
Induction / signalling / regulation of gene expression
Positional information
• determine the location relative to body axes
and cell’s ability to respond to signals
• anteriorposterior and dorsoventral axe
is done by gradients of maternal morphogenes=
=products of genes, transcription factors
Group of genes
1. egg-polarity genes - bicoid
Segmentation genes
2. Gap genes
3. Pair-rule genes
4. Segment polarity genes
Homeotic genes / Homeobox
• identity of body parts
• evolutionarily highly conserved
HOX genes:
origin of transctiption factors with homeodomain
able to bind to DNA / switch on or off
Zygote - cleavage
Morula - blastomers
Blastula / blastocoel / blastocyst
Gastrula – gastrulation
Organogenesis – primitive organs
Specific changes of shape, position and adhesion
Polarization / animal vegetal pole
Epiblast - embryo
Hypoblast - yolk sac
Germ layers / invagination
Ectoderm – nervous system, skin
Endoderm – pancreas, epitels of digestive system
Mesoderm – kidneys, heart, muscle
ectoderm forms the outer layer of gastrula
endoderm lines the digestive tract and
mesoderm fills the space between the ectoderm and
Animal kingdom
Porifera - sponges
Cnidaria – jellyfish, corals, anemones
Ctenophora – coma jellies
Platyhelminthes – flatworms
Nematoda – roundworms
Nemertea – ribbon worms
two germs layers
three germs layers
Protostomia / mouth from
Mollusca – clams, snails, octopuses
Annelida – segmented worms
Arthropoda – crustaceans, insects, spiders
Echinodermata – sea stars, sea urchins
Chordata – lancelets, tunicates, vertebrates
Coelom without segmetation
Coelom with segmentation
Segmentation homonomously
Sedmentation herenomously
Deuterostomia / anus from
blastopor, mouth secondarily
Body cavity
Space between
digestive tract
outer body wall
Organogenesis - chordata
Primitive organs from germ layers
folds, clefts, dense clumps – mechanisms
Neural tube - ektoderm – centre of nerve
system, brain and spinal cord
Notochord – mesoderm – backbone
Somites - mesoderm - the muscle segments
arrange along each side of notochord
neural tube
Chicken, mammals
Primitive streak “blastoporus”
a rapidly proliferating mass of cells that spreads
between the ectoderm and endoderm, giving rise
to the mesoderm layer.
Amniotic egg / reptiles, birds and mammals
Amnion / protection
Allantois / wastes
and gas exchange
Chorion / gas
Yolk sac
Human embryo
a slow rate of division - between 12 and 24 hours
Blastocyst – 7 days, more than 100 cells
Trofoblast – placenta
Primitive streak
Ectoderm: nervous system and epidermis
Endoderm: digestive tract and associated organs
Mesoderm: kidney, heart, muscles, inner layer of
In vertebrates, the
ectoderm has three
external ectoderm
(also known as
surface ectoderm),
the neural crest, and
neural tube.
The latter two are
known as
The body organs, tissues and systems derived from the
• bones
• cartilage
• most of the circulatory system, including the heart and major
blood vessels
• connective tissues of the gut and integuments
• mesenchyme
• mesothelium
• muscles
• peritoneum (lining of the abdominal cavity)
• reproductive system
• spleen
• urinary system, including the kidneys
The following chart shows the products produced by
the endoderm.
Gastrointestinal tract
Respiratory tract
Endocrine glands and organs (liver and pancreas)
The endoderm
forms the epithelial lining of the entire alimentary canal
except part of the mouth, pharynx and the terminal part
of the rectum (which are lined by involutions of the
ectoderm), the lining cells of all the glands which open
into the digestive tube, including those of the liver and
pancreas, the epithelium of the auditory tube and
tympanic cavity, of the trachea, bronchi, and alveoli of
the lungs, of the urinary bladder and part of the urethra,
and that which lines the follicles of the thyroid gland and
• Sensory organs
• Cuticle [skin] of more levels and with derivatives
• Special blood cells carry oxygen, closed circulatory system
• Pairing kidneys of mesoderm origin
• Nervous system and system of glands of internal secretions
operate all life functions
• Ability to deposite of molecules of high energy
- Land vertebrate have egg with
amniotic sac and allantois,
Agnatha and Gnathostomata from pharyngeal slits
• Mammals, birds, reptiles, amphibians, classes of fishes
Perfect thermoregulation - adaptation to fluctuating
Cornification of skin, hair
Epidermic glands, lactic, milk glands
Two-generation set of teeth
Two atrias, two ventriculi, left alveolar arch
Non-nucleated erythrocytes
Placenta / placental mammals and marsupials
Thank you for your attention
Campbell, Neil A., Reece, Jane
B., Cain Michael L., Jackson,
Robert B., Minorsky, Peter V.,
Biology, Benjamin-Cummings
Publishing Company, 1996 –