Development

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Development

• Introduction
• Early Stages of Development
• Quiz part 1
• Suites of Developmental Characters
• Quiz part 2

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In this tutorial, you will learn

• The basics of early development from
  fertilization through gastrulation.
• Major differences in early development between
  taxonomic groups.

Credits Figures and images by N. Wheat unless
otherwise noted. Starfish embryo photos courtesy
of K. Wynne. Sea urchin gastrulation, and frog
cleavage gastrulation videos courtesy of
TheDeepScis YouTube channel. Chick gastrulation
video courtesy of elishanathans YouTube
channel. Blastocyst image from Wikipedia. Funded
by Title V-STEM grant P031S090007.
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Introduction

• Development describes the changes in an organism
  from its earliest beginnings through maturity.

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Fertilization

• Fertilization is the initial event in development
  in sexual reproduction.
• Union of male and female gametes.
• Recombination of paternal and maternal genes.
• Restoration of the diploid number (two sets of
  chromosomes).

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Zygote

• The diploid cell resulting from fertilization is
  now called a zygote.

Photo courtesy of K. Wynne

• Photos in the following slides illustrate
  development in the starfish (Phylum
  Echinodermata).

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Cleavage

• Cleavage rapid cell divisions following
  fertilization.
• Very little growth occurs while the cells are
  dividing.
• Each cell called a blastomere.

4 cell stage
2 cell stage
Photos courtesy of K. Wynne
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Cleavage

• This video shows cleavage in a frog embryo

Cant view the video? Link To YouTube
http//www.youtube.com/user/TheDeepScip/u/5/UPJJ
wVNzaHw
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Morula

• Morula the name given to the solid ball of
  cells that results from cleavage.
• First 5-7 divisions.

Photo courtesy of K. Wynne
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Blastula

• As divisions continue, a fluid filled cavity, the
  blastocoel, forms within the embryo.
• The resulting hollow ball of cells is now called
  a blastula.

late blastula
early blastula
Photos courtesy of K. Wynne
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Gastrulation

• The morphogenetic process called gastrulation
  rearranges the cells of a blastula into a
  three-layered (triploblastic) embryo, called a
  gastrula, that has a primitive gut (archenteron).

early gastrula
late gastrula
Photos courtesy of K. Wynne
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The Blastopore

• The blastopore is the first opening in the embryo
  the point of invagination during gastrulation.
• The blastopore will eventually become either the
  mouth or the anus.
• One end of the gut-tube or the other.
• The space that forms during this time is the
  primitive gut, the archenteron.

Blastopore
Archenteron
Photo courtesy of K. Wynne
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Gastrulation

• The three tissue layers produced by gastrulation
  are called embryonic germ layers.
• The ectoderm forms the outer layer of the
  gastrula.
• Outer surfaces, neural tissue
• The endoderm lines the embryonic digestive tract.
• The mesoderm partly fills the space between the
  endoderm and ectoderm.
• Muscles, reproductive system

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Gastrulation Sea Urchin

• Gastrulation in a sea urchin produces an embryo
  with a primitive gut (archenteron) and three germ
  layers.

Cant view the video? Link To YouTube
http//www.youtube.com/user/TheDeepScip/u/3/Lgb4
wMsZwZA
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Gastrulation - Frog

• Result is again an embryo with gut 3 germ
  layers.
• Gastrulation in the frog is more complicated due
  to the moderate amount of yolk present in the
  egg.
• Blastula wall more than one cell thick.

Cant view the video? Link To YouTube
http//www.youtube.com/user/TheDeepScip/u/0/WSou
NeWnZ_0
15
Gastrulation - Chick

• Gastrulation in the chick is affected by the
  large amounts of yolk in the egg.
• Embryo essentially sits on top of large mass of
  yolk.

Cant view the video? Link To YouTube http//www
.youtube.com/watch?vu52pTXtg75s

• Primitive streak a groove on the surface along
  the future anterior-posterior axis.
• Functionally equivalent to blastopore lip in
  frog.

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Gastrulation - Mammal

• In mammals the blastula is called a blastocyst.
• Inner cell mass will become the embryo while
  trophoblast becomes part of the placenta.

Inner cell mass
Trophoblast
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Gastrulation - Mammal

• Gastrulation in mammals involves the inner cell
  mass and is similar to that of the chick due to
  the fact that mammalian ancestors and early
  mammals laid eggs.
• The large mass of yolk may be gone, but the
  developmental pattern remains.

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Shortly after fertilization, the zygote undergoes
a series of rapid cell divisions. This is called
Question 1

• Meiosis
• Gastrulation
• Organogenesis
• Cleavage

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During cleavage, each cell in the embryo is
called a
Question 2

• Blastula
• Morula
• Gastrula
• Blastomere

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The solid ball of cells that results from
cleavage is called
Question 3

• Blastula
• Morula
• Gastrula
• Blastomere

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A fluid filled space called the blastocoel forms
inside the embryo - at this point it is a
Question 4

• Blastula
• Morula
• Gastrula
• Blastomere

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The stage that results in three germ layers and a
primitive gut is the
Question 5

• Blastula
• Morula
• Gastrula
• Blastomere

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Which of the following is not one of the three
primary germ layers formed during gastrulation?
Question 6

• Endoderm
• Myoderm
• Mesoderm
• Ectoderm

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The difference in gastrulation found in different
types of animals is due primarily to
Question 7

• The amount of yolk present
• The size of the blastomeres
• Development in different species is completely
  unrelated
• None of the above

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Suites of Developmental Characters

• Two major groups of triploblastic animals
• Protostomes include flatworms, annelids and
  molluscs.
• Deuterostomes include echinoderms and chordates.

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Protostomes Deuterostomes

• Protostomes deuterostomes are differentiated
  by
• Spiral vs. radial cleavage
• Mosaic vs. regulative cleavage
• Blastopore becomes mouth vs. anus
• Schizocoelous vs. enterocoelous coelom formation.

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Spiral vs. Radial Cleavage

• Spiral cleavage occurs in most protostomes.
• Some ecdysozoans show radial or superficial
  (insects) cleavage.

• Radial cleavage is found in most deuterostomes.
• Tunicates and mammals have specialized cleavage
  patterns.

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Mosaic vs. Regulative Development

• Mosaic development cell fate is determined by
  the components of the cytoplasm found in each
  blastomere.
• An isolated blastomere cant develop.
• Protostomes

• Regulative development the fate of a cell
  depends on its interactions with neighbors, not
  what piece of cytoplasm it has.
• A blastomere isolated early in cleavage is able
  to from a whole individual (e.g. twins).
• Deuterostomes

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Fate of the Blastopore

• Protostome means first mouth.
• Blastopore becomes the mouth.
• The second opening will become the anus.

• Deuterostome means second mouth.
• The blastopore becomes the anus and the mouth
  develops as the second opening.

Blastopore
Photo courtesy of K. Wynne
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Coelom Formation

• The coelom is a body cavity found in many
  triploblastic organisms that is completely
  surrounded by mesoderm.
• Not all protostomes have a true coelom.
• Pseudocoelomates have a body cavity between
  mesoderm and endoderm.
• Acoelomates have no body cavity at all other than
  the gut.

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Coelom Formation

• In protostomes that have a coelom, a mesodermal
  band of tissue forms before the coelom is formed.
• In the process of coelom formation called
  schizocoely, this mesoderm splits to form a
  coelom.

• In enterocoely, the coelom forms as outpocketing
  of the gut.
• Typical deuterostomes have coeloms that develop
  by enterocoely.
• Vertebrates use a modified version of
  schizocoely.

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Radial cleavage is found primarily in which group?
Question 8

• Protostomes
• Deuterostomes
• Both groups show radial cleavage
• Neither group shows radial cleavage

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This figure shows
Question 9

• Radial cleavage
• Spiral cleavage
• A four-cell stage embryo
• A blastula

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Early in cleavage, a blastomere becomes isolated.
It grows into an entire separate individual. This
is an example of __________ development found in
____________.
Question 10

• Mosaic, protostomes
• Mosaic, deuterostomes
• Regulative, protostomes
• Regulative, deuterostomes

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The blastopore will become the mouth in
Question 11

• Protostomes
• Deuterostomes
• All animals
• Neither it forms something else

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Coel is a word-part that we see frequently. The
blastocoel is the space inside the blastula, the
coelom is a mesoderm-lined body cavity. What will
you find associated with coel words?
Question 12

• An organ like the heart
• A proliferation of cells
• A cavity or space
• It indicates a developmental stage

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Most protostomes show this type of coelom
formation where a band of mesoderm splits to form
the coelom.
Question 13

• Enterocoely
• A modified version of enterocoely
• Schizocoely
• A true coelom is never found in protostomes

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