1: NATURE AND SCOPE OF DEVELOPMENT Flashcards
interdisciplinary field that is at foundation of biology
accdg. to Barresi and Gilbert 2020
Developmental biology
Seeks to elucidate the cellular and molecular mechanism that drive changes in cells, tissues and organs over time - a timescale that spans all of life, from fertilization to aging.
Developmental biology
First known embryologist
Aristotle
Aristotle undertaken the first known study of _
comparative developmental anatomy
Aristotle’s On the Generation of Animals on life cycle themes:
- born from eggs (oviparity)
- born by live birth (viviparity)
- born by producing an egg that hatches inside the body (ovoviviparity)
- born from eggs
(oviparity)
- born by live birth
(viviparity)
- born by producing an egg that hatches inside the body
(ovoviviparity)
2 major cell division Aristotle identified by which embryos are formed
Holoblastic pattern
Meroblastic pattern
Patter of cleavage (in which the entire egg is divided into successively smaller eggs, as it is in frogs and mammals)
Holoblastic
pattern of cleavage (as in chicks, wherein only part of the
egg is destined to become the embryo, while the other portion—the yolk—serves as nutrition for the embryo)
meroblastic
concluded that all animals—even mammals—originate from
eggs
1651
▪ William Harvey
“all from egg” is the motto on the frontispiece of
Harvey’s On the Generation of Living Creatures, and this precluded the spontaneous generation of animals from __
ex ovo omnia
mud or excrement
William Harvey was the first to see the ____ (the small region of
the egg containing the yolk-free cytoplasm that gives rise to the embryo)
blastoderm of the chick embryo
William Harvey was the first to notice that ____ before the heart
does
“islands” of blood tissue form
he also suggested that the amniotic fluid might function as a “shock absorber” for the embryo
William Harvey
published the first microscopic account of chick
development
Marcello Malpighi
Marcello Malpighi
for the first time, the groove of the forming ____, the
____, and the ____ of the arteries and
veins—to and from the yolk—were identified
neural tube
muscle-forming somites
first circulation
built a microscope; discovered sperms in human
semen
Anton Van Leeuwenhoek
saw the mammalian egg under microscope
Karl Ernst von Baer
postulated that egg and sperm cells are equivalent
Matthias Jakob Schleiden and Theodor Schwann
discovered the fusion of sperm and egg nuclei during
fertilization in sea urchins; provided a conceptual basis for genetic inheritance and settled the long-standing debate on the role of the egg and sperm in
generation of new life
Oscar Hertwig
discovered and understand mitosis;
great step towards understanding growth and development
Walther Fleming (German biologist)
founder of the science of cytogenetics
Walther Fleming
Walther Fleming
- as the first to detail the chromosomal movements in the process of ____
- he used aniline dyes, a by-product of coal tar, to stain cells of
salamander embryos
mitosis
Walther Fleming discovered that “the nucleus always splits ____
before the cell does”
Walther Fleming
he was able to visualize the ____ as the cells divide
threadlike material (chromatin)
accurately drew pronuclear fusion in mouse
Johannes Sobotta
on Preformation versus Epigenesis (two persistent
ways of describing and seeking to explain the development of individual
organic form)
Thomas Hunt Morgan
the form of living things exists, in real terms, prior to
their development instead of assembly from parts; generation of
offspring occurs as a result of an unfolding and growth of preformed
parts
Preformation
the embryological theory according to which “organs […]
are progressively formed from, or emerge from, an originally
undifferentiated, homogenous [material]” (Smith 1976, p. 264). …;
▪ for Aristotle, ____ could be seen as a general process that
explained the development of a form
epigenesis
3 to 4 decades of 20th Century
▪ genetics and embryology remained disconnected
▪ celebrated embryologists in 1930 (Frank Lillie, H. Spemann, R. Harrison and E. E. Just) did not think that ____ have anything to do with early embryonic
development
▪ they claimed that geneticists had no mechanism to explain how the same
nuclear genes could create different cell types during development
genes
believed in the relationship between inducer and
competent tissues paralleled that of the genes and the cytoplasm
Conrad Hal Waddington
Conrad Hal Waddington
genes and the cytoplasm were in ____
continual dialogue
he said that, “Neither cytoplasm nor nucleus can be disregarded: in fact the
most important subject to discuss is how they affect each other”
an evolutionary morphologist, argued that some
directing substance or substances had to exist to cause the egg of one species
to develop differently from that of another species even though the eggs look
identical and are in the same environment
William Keith Brooks
linked heredity to development
William Keith Brooks
– combined genetics and embryology
B. Ephrussi, G.W. Beadle
B. Ephrussi, G.W. Beadle traced the pathway through which the vermilion and related genes
affected or determined eye color of
Drosophila
transplantation of mutant imaginal disks fated to become eyes
into wild-type larvae led to demonstration of distinct diffusible
substances manufactured or controlled by wild-type alleles at
the vermilion and cinnabar loci, which controlled distinct steps
in the formation of the brown component of normal Drosophila
eye
is the study of the process by which organisms grow and
develop
Developmental Biology
Modern Developmental Biology now studies the genetic control of:
▪ Cell Growth;
▪ Cell Differentiation; and
▪ Morphogenesis
a subfield, is the study of the organisms between the one-cell stage (zygote) and
the end of the embryonic stage, which is not necessarily the beginning of free
living.
Embryology
embryonic development involves
cell division, cell growth, morphogenesis and
cell differentiation.
all these processes are involved in the formation of specialized tissues, organs
and organ systems of the new individual
describes the origin and the development of an organism from the
fertilized egg to its mature form
ontogenesis
describes the process by which cells acquire a “type”
Cell Differentiation
involves structural and functional divergence of cells as they become
specialized during a multicellular organism’s development, dependent on the
control of gene expression, thus, the morphology of a cell may change
dramatically during differentiation but the genetic material remains the same,
with few exceptions
cell that is able to differentiate into many cell types
Pluripotent
types of Pluripotent
o Stem cells – in animals
o Meristematic cells – in higher plants
cell that is able to differentiate into all cell types
Totipotent
types of Totipotent
Zygote and Early Embryonic cells – in mammals
Embryonic cells are ____ because they have the ability to
retain the potential to form all parts of the animal.
totipotent
In plants, many differentiated cells can become totipotent with
simple laboratory techniques.
in most multicellular organisms, ____ cells are alike
not all
for example, cells that make up the skin are different from cells that
make up the inner organs. Yet, all of the different cell types in the human
body are all derived from a single fertilized egg through differentiation
a process by which an unspecialized cell becomes specialized
into one of the many cells that make up the body, such as heart, liver or muscle
cell
differentiation
during differentiation, certain genes are turned on or activated while other genes
are switched off or inactivated; this process is intricately regulated
▪ as a result, a differentiated cell will develop specific structures and perform
certain functions
▪ differentiation can involve changes in numerous aspects of cell physiology; ____ can all change during differentiation
- size,
- shape,
- polarity,
- metabolic activity,
- responsiveness to signals and
- gene expression profiles
in cytopathology, the ____ is used as a measure of
cancer progression
level of cellular differentiation
three basic categories of cells that make up the mammalian body
- Germ (Sex) Cells
- Somatic (Body) Cells
- Stem Cells
each of the approximately 100, 000, 000, 000, 000 cells in an adult human has
its own copy or copies of the genome (genetic material of an organism), with
the only exception being certain cell types that lack nuclei in their fully
differentiated state, such as ____
red blood cells
the majority of these cells are ____ or have two copies of each chromosome; these cells are called somatic cells
o it includes most of the cells that make up the human body, such as skin
and muscle cells
diploid (2n)
are any line of cells that give rise to gametes- eggs and sperm and are continuous through the generations
Germ line cells
have the ability to divide for indefinite period and
to give rise to specialized cells
Stem cells,
Morphogenesis came from the Greek
morphe “shape” and genesis “creation”
one of the three fundamental aspects of developmental biology along with the
control of cell growth and cell differentiation
Morphogenesis
concerned with the shapes of tissues, organs and entire organisms and the
positions of the various specialized cell types
Morphogenesis
it involves an attempt to understand the process that control the organized
spatial distribution of cells that arises during the embryonic development of an
organism which give rise to the characteristic form of tissues, organs and overall
body anatomy
Morphogenesis
Morphogenesis
in the human embryo, the change from a cluster of nearly identical cells at the
____ embryo with structured tissues and organs
is controlled by the genetic “program” and can be modified by environmental
factors
blastula stage to the post-gastrulation
several important molecules that are important during morphogenesis are:
- Morphogens
- Transcription Factor Proteins
- Molecules that control Cell Adhesion
– Example, during gastrulation clumps
of stem cells switch off their cell-to-cell adhesion, become migratory, and take
up new positions with an embryo where they again activate specific cell
adhesion proteins and form new tissues and organs
Molecules that control Cell Adhesion
determine the fate of cells by interacting with
DNA; these can be coded for by master regulatory genes and either activate or
deactivate the transcription other genes and in turn, these secondary gene
products can regulate the expression of still other genes in a regulatory cascade
Transcription Factor Proteins
soluble molecules that can diffuse and carry signals that control
cell differentiation decisions in a concentration-dependent fashion; they
typically act through binding to specific protein receptors
Morphogens
the process individual development from a single cell, an egg cell
or a zygote, to an adult organism
Ontogeny
stages
of development
- fertilization,
- cleavage,
- gastrulation,
- organogenesis,
- hatching (or birth),
- metamorphosis, and
- gametogenesis
The stages of development between fertilization
and hatching (or birth) are collectively called
embryogenesis
involves the fusion of the mature sex cells - sperm and egg, which are
collectively known as gametes
Fertilization
fusion of the gamete cells stimulates the egg to begin development and
____
initiates a new individual
subsequent fusion of the gamete nuclei (the male and female pronuclei,
each of which has ____the normal number of chromosomes
characteristic for the species) gives the embryo its genome (collection
of genes that helps instruct the embryo to develop in a manner very
similar to its parents)
only half
series of mitotic divisions that immediately follow fertilization
Cleavage
Cleavage
enormous volume of zygote cytoplasm is divided into numerous smaller
cells called
blastomeres
by the end of cleavage, the blastomeres have usually formed a sphere,
known as a
blastula
after the rate of mitotic division slows down, blastomeres undergo
dramatic movements & change their positions relative to one another
Gastrulation
series of extensive cell rearrangements is called
gastrulation
(embryo is said to be in the gastrula stage)
as a result of gastrulation, the embryo contains ____ that will interact to generate the
organs of the body
three germ layers
(endoderm, ectoderm, and mesoderm)
germ layers
forms exoskeleton
ectoderm
germ layers
develops into organs
mesoderm
germ layers
forms the inner lining of organs
endoderm
once the germ layers are established, the cells interact with one another
and rearrange themselves to produce tissues and organs
organogenesis
organogenesis
____ are exchanged between the cells of the germ layers
(resulting in the formation of specific organs at specific sites)
chemical signals
organogenesis
certain cells will undergo long migrations from their place of origin to
their final location
o these migrating cells include the precursors of ____
- blood cells,
- lymph cells,
- pigment cells, and
- gametes (eggs and sperm)
in most species, the organism that hatches from the egg or is born into
the world is ______
not sexually mature
organism needs to undergo ____ to become a sexually
mature adult
metamorphosis
in most animals, the young organism is called a ____ (may look
significantly different from the adult)
larva
in some species, the larval stage is the one that lasts the ____,
and is used for feeding or dispersal
longest
▪ in such species, the adult is a brief stage whose sole
purpose is to reproduce
▪ E.g. silkworm moths, for instance, the adults do not have
mouthparts and cannot feed; the larva must eat enough
so that the adult has the stored energy to survive and
mate. Indeed, most female moths mate as soon as they
enclose from the pupa, and they fly only once—to mate
and lay their eggs. Then they die.
in many species, a group of cells is set aside to produce the next
generation (rather than forming the current embryo)
Gametes
- these cells are the precursors of the gametes
- gametes and their precursor cells are collectively called germ cells (set aside for reproductive function)
- All other cells of the body are called somatic cells
- this separation of somatic cells (which give rise to the individual body) and germ cells (which contribute to the formation of a new generation) is often one of the first differentiations to occur during animal development
the germ cells eventually migrate to the ____, where they differentiate
into gametes
gonads
The development of gametes (gametogenesis), is usually ____
until the organism has become physically mature
not completed
at maturity, the gametes may be released and participate in
fertilization to begin a new embryo
After these, the adult organism eventually undergoes ____, its
nutrients often supporting the early embryogenesis of its offspring and its absence
allowing less competition. Thus, the cycle of life is renewed
senescence and dies
the process of the fetus passing from the uterus into the outside world
Birth
the act of conceiving or becoming pregnant; synonymous with
fertilization
Conception
means “growing within” and refers to the “human offspring in the
first eight weeks following fertilization”
Embryo
the first 8 weeks of human development starting with
fertilization; characterized by the formation of most
major body systems
Embryonic Period
the process that starts with the sperm entering the egg or
oocyte, and ends with the joining of the female and male DNA
within the single cell zygote
Fertilization
the time from the end of eight weeks through the end of
pregnancy; during this time the body grows larger and its
systems begin to function
Fetal Period
means “unborn offspring” and refers to human offspring from 8 weeks
after fertilization until birth
Fetus
the period of time around birth, from week 28 of pregnancy
until 7 days after birth
Perinatal Period
the period of time following birth
Postnatal
the condition of a female from the time of fertilization of her
oocyte until birth, normally lasting 38 weeks for humans (or 40
weeks if measured from a woman’s last menstrual period)
Pregnancy
human development occurring between fertilization
and birth
Prenatal Development
the period of time from fertilization until birth; ’pre’ means
before, ’natal’ means ’relating to birth’
Prenatal Period
three month periods used to divide pregnancy into three stages
of approximately equal length
Trimesters
the single-cell embryo that results from the joining of the sperm and
oocyte; means “yoked or joined together”
Zygote
