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An embryo is the early stage of development of a
multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biol ...
. In general, in
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological me ...

organism
s that reproduce sexually, embryonic development is the part of the life cycle that begins just after
fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilization
and continues through the formation of body structures, such as tissues and organs. Each embryo starts development as a
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
, a single cell resulting from the fusion of
gamete A gamete ( /ˈɡæmiːt/; from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply ...
s (i.e. the process of fertilization which is the fusion of a female
egg cell The egg cell, or ovum (plural ova), is the female reproductive Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduct ...
and a male
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...

sperm
cell). In the first stages of embryonic development, a single-celled zygote undergoes many rapid cell divisions, called
cleavage Cleavage may refer to: Science * Cleavage (crystal), in mineralogy and materials science, a process of splitting a crystal * Cleavage (geology), the foliation perpendicular to stress as a result of ductile deformation * Cleavage (embryo), in embr ...
, to form a
blastula Blastulation is the stage in early animal embryonic development An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism that consists of more than one cell (biology), cell, in contrast ...

blastula
, which looks similar to a ball of cells. Next, the cells in a blastula-stage embryo start rearranging themselves into layers in a process called
gastrulation Gastrulation is the stage in the early embryonic development ''Embryonic'' is the twelfth studio album by experimental rock Experimental rock, also called avant-rock, is a subgenre of rock music that pushes the boundaries of common composition a ...

gastrulation
. These layers will each give rise to different parts of the developing multicellular organism, such as the nervous system, connective tissue, and
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
. A newly developing human is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism tha ...

fetus
. In other multicellular organisms, the word "embryo" can be used more broadly to any early developmental or life cycle stage prior to
birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fe ...

birth
or
hatching Hatching (''hachure'' in French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République française), is a country primarily lo ...

hatching
.


Etymology

First attested in English in the mid-14c., the word ''embryon'' derives from
Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share ...
''embryo'', itself from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
(''embruon''), lit. "young one", which is the neuter of (''embruos''), lit. "growing in", from ἐν (''en''), "in" and βρύω (''bruō''), "swell, be full"; the proper
Latinized Latinisation or Latinization can refer to: * Latinisation of names, the practice of rendering a non-Latin name in a Latin style * Latinisation in the Soviet Union, the campaign in the USSR during the 1920s and 1930s to replace traditional writing sy ...
form of the Greek term would be ''embryum''.


Development


Animal embryos

In animals, fertilization begins the process of embryonic development with the creation of a zygote, a single cell resulting from the fusion of gametes (e.g. egg and sperm). The development of a zygote into a multicellular embryo proceeds through a series of recognizable stages, often divided into cleavage, blastula, gastrulation, and organogenesis. Cleavage is the period of rapid mitotic cell divisions that occur after fertilization. During cleavage, the overall size of the embryo does not change, but the size of individual cells decrease rapidly as they divide to increase the total number of cells. Cleavage results in a blastula. Depending on the species, a blastula stage embryo can appear as a ball of cells on top of yolk, or as a hollow sphere of cells surrounding a middle cavity. The embryo's cells continue to divide and increase in number, while molecules within the cells such as RNAs and proteins actively promote key developmental processes such as gene expression, cell fate specification, and polarity. Gastrulation is the next phase of embryonic development, and involves the development of two or more layers of cells (germinal layers). Animals that form two layers (such as
Cnidaria Pacific sea nettles, ''Chrysaora fuscescens'' Cnidaria () is a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, ...

Cnidaria
) are called diploblastic, and those that form three (most other animals, from
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a count ...

flatworm
s to humans) are called triploblastic. During gastrulation of triploblastic animals, the three germinal layers that form are called the
ectoderm The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all species of animal Animals (also ...

ectoderm
,
mesoderm The mesoderm is the middle layer of the three germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoa ...

mesoderm
, and
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small r ...
. All tissues and organs of a mature animal can trace their origin back to one of these layers. For example, the ectoderm will give rise to the skin epidermis and the nervous system, the mesoderm will give rise to the vascular system, muscles, bone, and connective tissues, and the endoderm will give rise to organs of the digestive system and epithelium of the digestive system and respiratory system. Many visible changes in embryonic structure happen throughout gastrulation as the cells that make up the different germ layers migrate and cause the previously round embryo to fold or invaginate into a cup-like appearance. Past gastrulation, an embryo continues to develop into a mature multicellular organism by forming structures necessary for life outside of the womb or egg. As the name suggests, organogenesis is the stage of embryonic development when organs form. During organogenesis, molecular and cellular interactions prompt certain populations of cells from the different germ layers to differentiate into organ-specific cell types. For example, in neurogenesis, a subpopulation of cells from the ectoderm segregate from other cells and further specialize to become the brain, spinal cord, or peripheral nerves. The embryonic period varies from species to species. In human development, the term fetus is used instead of embryo after the ninth week after conception, whereas in
zebrafish The zebrafish (''Danio rerio'') is a freshwater fish are common freshwater fish throughout temperate Eurasia. Freshwater fish are those that spend some or all of their lives in fresh water, such as river A river is a natural flowing wate ...

zebrafish
, embryonic development is considered finished when a bone called the
cleithrum The cleithrum is a membrane bone which first appears as part of the skeleton in primitive bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse Taxonomy (biology), taxonomic group of fish that have skeletons primarily c ...
becomes visible. In animals that hatch from an egg, such as birds, a young animal is typically no longer referred to as an embryo once it has hatched. In vivaparous animals (animals whose offspring spend at least some time developing within a parent's body), the offspring is typically referred to as an embryo while inside of the parent, and is no longer considered an embryo after birth or exit from the parent. However, the extent of development and growth accomplished while inside of an egg or parent varies significantly from species to species, so much so that the processes that take place after hatching or birth in one species may take place well before those events in another. Therefore, according to one textbook, it is common for scientists interpret the scope of
embryology Embryology (from Ancient Greek, Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logy, -logia'') is the branch of biology that studies the Prenatal development (biology), prenatal development of gametes (sex cells), ...
broadly as the study of the development of animals.


Plant embryos

Flowering plants (
angiosperms Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...

angiosperms
) create embryos after the fertilization of a haploid
ovule In seed plant The spermatophytes, also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plants that produce seeds, hence the alternative name seed plants. They are a subset of the embryophytes or l ...

ovule
by
pollen Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the ga ...

pollen
. The DNA from the ovule and pollen combine to form a diploid, single-cell zygote that will develop into an embryo. The zygote, which will divide multiple times as it progresses throughout embryonic development, is one part of a
seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seed
. Other seed components include the
endosperm 350px, right The endosperm is a tissue produced inside the seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The ...
, which is tissue rich in nutrients that will help support the growing plant embryo, and the seed coat, which is a protective outer covering. The first cell division of a zygote is , resulting in an embryo with one small cell (the apical cell) and one large cell (the basal cell). The small, apical cell will eventually give rise to most of the structures of the mature plant, such as the stem, leaves, and roots. The larger basal cell will give rise to the suspensor, which connects the embryo to the endosperm so that nutrients can pass between them. The plant embryo cells continue to divide and progress through developmental stages named for their general appearance: globular, heart, and torpedo. In the globular stage, three basic tissue types (dermal, ground, and vascular) can be recognized. The dermal tissue will give rise to the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...
or outer covering of a plant, ground tissue will give rise to inner plant material that functions in
photosynthesis Photosynthesis is a process used by plants and other organisms to into that, through , can later be released to fuel the organism's activities. Some of this chemical energy is stored in molecules, such as s and es, which are synthesized fro ...

photosynthesis
, resource storage, and physical support, and vascular tissue will give rise to connective tissue like the
xylem Xylem is one of the two types of transport in s, the other being . The basic function of xylem is to transport from roots to stems and leaves, but it also transports . The word ''xylem'' is derived from the word (''xylon''), meaning "wood"; ...

xylem
and
phloem Phloem (, ) is the living tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa d ...

phloem
that transport fluid, nutrients, and minerals throughout the plant. In heart stage, one or two
cotyledon File:Germination-en.svg, 335px, Schematic of epigeal vs hypogeal germination A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one o ...
s (embryonic leaves) will form.
Meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s (centers of
stem cell In multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties o ...
activity) develop during the torpedo stage, and will eventually produce many of the mature tissues of the adult plant throughout its life. At the end of embryonic growth, the seed will usually go dormant until germination. Once the embryo begins to
germinate seedlings, three days after germination Germination is the process by which an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell t ...

germinate
(grow out from the seed) and forms its first true leaf, it is called a
seedling A seedling is a young sporophyte '' Tortula muralis''. In mosses, the gametophyte is the dominant generation, while the sporophytes consist of sporangium-bearing stalks growing from the tips of the gametophytes A sporophyte () is the dip ...

seedling
or plantlet. Plants that produce
spore )'', growing on a thinning, thinned hybrid black poplar ''(populus, Populus x canadensis)''. The last stage of the moss#Life cycle, moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is ...
s instead of seeds, like
bryophyte Bryophytes are an informal group consisting of three divisions Division or divider may refer to: Mathematics *Division (mathematics) Division is one of the four basic operations of arithmetic, the ways that numbers are combined to make new nu ...

bryophyte
s and
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia art ...

fern
s, also produce embryos. In these plants, the embryo begins its existence attached to the inside of the
archegonium 240px, Diagram of archegonium anatomy An archegonium (pl: archegonia), from the ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 3 ...

archegonium
on a parental
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all ...
from which the egg cell was generated. The inner wall of the archegonium lies in close contact with the "foot" of the developing embryo; this "foot" consists of a bulbous mass of cells at the base of the embryo which may receive nutrition from its parent gametophyte. The structure and development of the rest of the embryo varies by group of plants. Since all land plants create embryos, they are collectively referred to as
embryophyte The Embryophyta (), or land plants, are the most familiar group of green plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that w ...

embryophyte
s (or by their scientific name, Embryophyta). This, along with other characteristics, distinguishes land plants from other types of plants, such as
algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grouping that includes species from multiple distinct s. Included organisms range from , such as '','' and the s, to forms, such as the , a large whi ...

algae
, which do not produce embryos.


Research and technology


Biological processes

Embryos from numerous plant and animal species are studied in biological research laboratories across the world to learn about topics such as
stem cell In multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties o ...
s, evolution and development,
cell division Cell division is the process by which a parent cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religiou ...

cell division
, and
gene expression Gene expression is the process by which information from a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, ...

gene expression
. Examples of scientific discoveries made while studying embryos that were awarded the
Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly , native_name_lang = , image = Nobel Assembly at Karolinska Institutet.jpeg , size = , motto = , formation = 190113 March 1978(as a forma ...
include the
Spemann-Mangold organizerThe Spemann-Mangold organizer is a group of cells that are responsible for the induction of the neural tissues during development in amphibian embryos. First described in 1924 by Hans Spemann and Hilde Mangold, the introduction of the organizer provi ...
, a group of cells originally discovered in amphibian embryos that give rise to neural tissues, and genes that give rise to body segments discovered in ''
Drosophila ''Drosophila'' () is a genus of fly, flies, belonging to the family (biology), family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the character ...

Drosophila
'' fly embryos by
Christiane Nüsslein-Volhard Christiane (Janni) Nüsslein-Volhard (born 20 October 1942) is a German developmental biologist and 1995 Nobel Prize-winner. Nüsslein-Volhard earned her PhD in 1974 from the University of Tübingen, where she studied protein-DNA interaction. ...
and
Eric Wieschaus Eric Francis Wieschaus (born June 8, 1947 in South Bend, Indiana South Bend is a city in, and the county seat A county seat is an administrative center, seat of government, or capital city of a county or Parish (administrative division), civi ...

Eric Wieschaus
.


Assisted reproductive technology

Creating and/or manipulating embryos via
assisted reproductive technology Assisted reproductive technology (ART) includes medical procedures used primarily to address infertility. This subject involves procedures such as in vitro fertilization, intracytoplasmic sperm injection (ICSI), cryopreservation of gametes or embryo ...
(ART) is used for addressing fertility concerns in humans and other animals, and for
selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding Animal breeding is a branch of animal science Animal science (also bioscience) is described as "studying the biology Biology i ...
in agricultural species. Between the years 1987 and 2015, ART techniques including
in vitro fertilization In vitro fertilisation (IVF) is a process of fertilisation Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new in ...
(IVF) were responsible for an estimated 1 million human births in the United States alone. Other clinical technologies include
preimplantation genetic diagnosis Pre-implantation genetic diagnosis (PGD or PIGD) is the genetic profiling of embryos prior to implantation (as a form of embryo profiling), and sometimes even of oocytes prior to fertilization. PGD is considered in a similar fashion to prenat ...

preimplantation genetic diagnosis
(PGD), which can identify certain serious genetic abnormalities, such as
aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more ploidy#Haploid and monoploid, c ...
, prior to selecting embryos for use in IVF. Some have proposed (or even attempted - see
He Jiankui affair The He Jiankui affair is a scientific and bioethical controversy concerning the use of genome editing Genome editing, or genome engineering, or gene editing, is a type of genetic engineering in which DNA is inserted, deleted, modified or rep ...
)
genetic editing Genetic editing (French language, French ''critique génétique''; German language, German ''genetische Kritik'') is an approach to scholarly editing in which an Exemplar (textual criticism), exemplar is seen as derived from a dossier of other manus ...
of human embryos via CRISPR-Cas9 as a potential avenue for preventing disease; however, this has been met with widespread condemnation from the scientific community. ART techniques are also used to improve the profitability of agricultural animal species such as cows and pigs by enabling selective breeding for desired traits and/or to increase numbers of offspring. For example, when allowed to breed naturally, cows typically produce one calf per year, whereas IVF increases offspring yield to 9-12 calves per year. IVF and other ART techniques, including
cloning Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means. In nature, some organisms produce clones through asexual reproduction Asexual reproduction is a type o ...

cloning
via interspecies somatic cell nuclear transfer (iSCNT), are also used in attempts to increase the numbers of endangered or vulnerable species, such as Northern white rhinos,
cheetah The cheetah (''Acinonyx jubatus'') is a large Felidae, cat native to Africa and central Iran. It is the Fastest animals, fastest land animal, estimated to be capable of running at with the fastest reliably recorded speeds being , and as suc ...

cheetah
s, and
sturgeon Sturgeon is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is s ...

sturgeon
s.


Cryoconservation of plant and animal biodiversity

Cryoconservation of genetic resources involves collecting and storing the reproductive materials, such as embryos, seeds, or gametes, from animal or plant species at low temperatures in order to preserve them for future use. Some large-scale animal species cryoconservation efforts include "
frozen zooA frozen zoo is a storage facility in which genetic materials taken from animals (e.g. DNA, sperm, Egg (biology), eggs, embryos and live tissue) are stored at very low temperatures (−196 °C) in tanks of liquid nitrogen. Material preserved in ...
s" in various places around the world, including in the UK's Frozen Ark, the Breeding Centre for Endangered Arabian Wildlife (BCEAW) in the United Arab Emirates, and the
San Diego Zoo The San Diego Zoo is a zoo in Balboa Park (San Diego), Balboa Park, San Diego, California, housing over 12,000 animals of more than 650 species and subspecies on of Balboa Park leased from the City of San Diego. Its parent organization, San Dieg ...

San Diego Zoo
Institute for Conservation in the United States. As of 2018, there were approximately 1,700 seed banks used to store and protect plant biodiversity, particularly in the event of mass extinction or other global emergencies. The
Svalbard Global Seed Vault The Svalbard Global Seed Vault ( no, Svalbard globale frøhvelv) is a secure seed bank on the Norway, Norwegian island of Spitsbergen in the remote Arctic Svalbard archipelago. Conservationist Cary Fowler, in association with the Consultative Gr ...
in Norway maintains the largest collection of plant reproductive tissue, with more than a million samples stored at .


Fossilized embryos

Fossilized animal embryos are known from the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologi ...

Precambrian
, and are found in great numbers during the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These perio ...
period. Even fossilized
dinosaur Dinosaurs are a diverse group of reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) a ...

dinosaur
embryos have been discovered.


See also

* Embryo loss *
Plant embryogenesis Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling ...
*
Pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual repr ...

Pregnancy
*
Prenatal development Prenatal development () includes the development of the embryo and of the foetus during a viviparous animal's gestation. Prenatal development starts with fertilization , in the germinal stage of embryonic development, and continues in fetal d ...

Prenatal development
*
In vitro fertilisation In vitro fertilisation (IVF) is a process of fertilisation Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative f ...
*
ProembryoProembryo, or pro-embryo, in a flowering plant The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of Embryophyte, land plants, with 64 Order(biology), orders, 416 Family (biology), families, approx ...
*
Miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the natural loss of an embryo or fetus before it is fetal viability, able to survive independently. Some use the cutoff of 20 weeks of gestation, after whi ...
*
Abortion Abortion is the ending of a pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young born of living organism, organisms, produced either by a single organism ...

Abortion


Notes


External links


UNSW Embryology - Educational website

A Comparative Embryology Gallery

4-H Embryology, University of Nebraska-Lincoln Extension in Lancaster County
* {{Authority control Developmental biology Bioethics Fertility medicine Articles containing video clips