View source for Biology:Embryo

{{short description|Multicellular diploid eukaryote in its earliest stage of development}}
{{Infobox embryology
| Name        = Embryo
| Latin       =
| Image      = Embryo 7 weeks after conception.jpg
| Caption    = A male [[Biology:Human|human]] embryo, seven weeks old<br /> or nine weeks' gestational age
}}

An '''embryo''' is an initial stage of development of a [[Biology:Multicellular organism|multicellular organism]]. In organisms that [[Biology:Sexual reproduction|reproduce sexually]], [[Biology:Embryonic development|embryonic development]] is the part of the life cycle that begins just after fertilization of the female [[Biology:Egg cell|egg cell]] by the male sperm cell. The resulting fusion of these two cells produces a single-celled [[Biology:Zygote|zygote]] that undergoes many [[Biology:Cleavage (embryo)|cell divisions]] that produce [[Biology:Cell|cells]] known as [[Biology:Blastomere|blastomere]]s. The blastomeres are arranged as a solid ball that when reaching a certain size, called a [[Biology:Morula|morula]], takes in fluid to [[Biology:Cavitation (embryology)|create a cavity]] called a [[Biology:Blastocoel|blastocoel]]. The structure is then termed a [[Biology:Blastula|blastula]], or a [[Biology:Blastocyst|blastocyst]] in [[Biology:Mammal|mammal]]s.

The mammalian blastocyst [[Biology:Zona hatching|hatches]] before [[Biology:Implantation (embryology)|implantating]] into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of [[Biology:Gastrulation|gastrulation]], neurulation, and [[Biology:Organogenesis|organogenesis]]. Gastrulation is the formation of the three [[Biology:Germ layer|germ layer]]s that will form all of the different parts of the body. Neurulation forms the [[Biology:Nervous system|nervous system]], and organogenesis is the development of all the various tissues and organs of the body.

A [[Biology:Human embryonic development|newly developing human]] is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a [[Biology:Fetus|fetus]]. In other multicellular organisms, the word "embryo" can be used more broadly to any early developmental or life cycle stage prior to [[Biology:Birth|birth]] or [[Biology:Hatchling|hatching]].

==Etymology==
First attested in English in the mid-14c., the word ''embryon'' derives from [[Social:Medieval Latin|Medieval Latin]] ''embryo'', itself from [[Social:Greek language|Greek]] {{lang|grc|ἔμβρυον}} (''embruon''), lit. "young one",<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29%2Fmbruon ἔμβρυον] {{webarchive|url=https://web.archive.org/web/20130531161449/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29%2Fmbruon |date=2013-05-31 }}, Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref> which is the neuter of {{lang|grc|ἔμβρυος}} (''embruos''), lit. "growing in",<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29%2Fmbruos ἔμβρυος] {{webarchive|url=https://web.archive.org/web/20130531041203/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29%2Fmbruos |date=2013-05-31 }}, Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref> from ἐν (''en''), "in"<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29n ἐν] {{webarchive|url=https://web.archive.org/web/20130531101258/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3De%29n |date=2013-05-31 }}, Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref> and βρύω (''bruō''), "swell, be full";<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dbru%2Fw βρύω] {{webarchive|url=https://web.archive.org/web/20130531101318/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dbru%2Fw |date=2013-05-31 }}, Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref> the proper [[Social:Latinisation of names|Latinized]] form of the Greek term would be ''embryum''.

==Development==
===Animal embryos===
{{Main|Biology:Animal embryonic development}}
[[File:Embryonic development of a salamander, filmed in the 1920s.ogv|thumb|Embryonic development of salamander, circa the 1920s]]
[[File:Wrinkledfrog embryos.jpg|thumb|Embryos (and one [[Biology:Tadpole|tadpole]]) of the wrinkled frog (''Rana rugosa'')]]
[[File:Mouse and Snake Embryos.jpg|thumb|[[Biology:Mouse|Mouse]] and snake 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).<ref>{{Cite journal|url=https://opentextbc.ca/biology/chapter/24-6-fertilization-and-early-embryonic-development/|title=24.6. Fertilization and Early Embryonic Development – Concepts of Biology – 1st Canadian Edition|website=opentextbc.ca|date=14 May 2015|access-date=2019-10-30|last1=Molnar|first1=Charles}}</ref> The development of a zygote into a multicellular embryo proceeds through a series of recognizable stages, often divided into cleavage, blastula, gastrulation, and organogenesis.<ref name=":0">{{Cite journal|last=Gilbert|first=Scott F.|date=2000|title=The Circle of Life: The Stages of Animal Development|url=https://www.ncbi.nlm.nih.gov/books/NBK9981/|journal=Developmental Biology. 6th Edition|language=en}}</ref>

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.<ref>{{Cite web|url=http://11e.devbio.com/wt0102.html|title=DevBio 11e|website=11e.devbio.com|access-date=2019-11-07}}</ref> Cleavage results in a blastula.<ref name=":0" />

Depending on the species, a blastula or [[Biology:Blastocyst|blastocyst]] stage embryo can appear as a ball of cells on top of yolk, or as a hollow sphere of cells surrounding a [[Biology:Blastocoel|middle cavity]].<ref name=":1">{{Cite book|title=An Introduction to Embryology|last=Balinsky|first=Boris Ivan|publisher=W.B. Saunders Company|year=1975|isbn=0-7216-1518-X|edition=Fourth}}</ref> 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.<ref>{{Cite journal|last=Heasman|first=Janet|date=2006-04-01|title=Patterning the early Xenopus embryo|journal=Development|language=en|volume=133|issue=7|pages=1205–1217|doi=10.1242/dev.02304|issn=0950-1991|pmid=16527985|doi-access=free}}</ref> Before [[Biology:Implantation (embryology)|implanting]] into the uterine wall the embryo is sometimes known as the ''pre-implantation embryo'' or ''pre-implantation conceptus''.<ref name="Niakan">{{cite journal |last1=Niakan |first1=KK |last2=Han |first2=J |last3=Pedersen |first3=RA |last4=Simon |first4=C |last5=Pera |first5=RA |title=Human pre-implantation embryo development. |journal=Development |date=March 2012 |volume=139 |issue=5 |pages=829–41 |doi=10.1242/dev.060426 |pmid=22318624|pmc=3274351 }}</ref> Sometimes this is called the '''pre-embryo''' a term employed to differentiate from an embryo proper in relation to embryonic stem cell discourses.<ref name="Jones">{{cite journal |last1=Jones |first1=DG |last2=Telfer |first2=B |title=Before I was an embryo, I was a pre-embryo: or was I? |journal=Bioethics |date=January 1995 |volume=9 |issue=1 |pages=32–49 |doi=10.1111/j.1467-8519.1995.tb00299.x |pmid=11653031}}</ref>

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 [[Biology:Cnidaria|Cnidaria]]) are called diploblastic, and those that form three (most other animals, from [[Biology:Flatworm|flatworm]]s to humans) are called triploblastic. During gastrulation of triploblastic animals, the three germinal layers that form are called the [[Biology:Ectoderm|ectoderm]], [[Biology:Mesoderm|mesoderm]], and [[Biology:Endoderm|endoderm]].<ref name=":1" /> All tissues and organs of a mature animal can trace their origin back to one of these layers.<ref>{{Cite journal|last1=Favarolo|first1=María Belén|last2=López|first2=Silvia L.|date=2018-12-01|title=Notch signaling in the division of germ layers in bilaterian embryos|journal=Mechanisms of Development|volume=154|pages=122–144|doi=10.1016/j.mod.2018.06.005|pmid=29940277|issn=0925-4773|doi-access=free}}</ref> For example, the ectoderm will give rise to the skin epidermis and the nervous system,<ref>{{Cite web|url=https://embryo.asu.edu/pages/ectoderm|title=Ectoderm {{!}} The Embryo Project Encyclopedia|website=embryo.asu.edu|language=en|access-date=2019-11-07}}</ref> the mesoderm will give rise to the vascular system, muscles, bone, and connective tissues,<ref>{{Cite web|url=https://embryo.asu.edu/pages/mesoderm|title=Mesoderm {{!}} The Embryo Project Encyclopedia|website=embryo.asu.edu|language=en|access-date=2019-11-07}}</ref> and the endoderm will give rise to organs of the digestive system and [[Biology:Epithelium|epithelium]] of the digestive system and respiratory system.<ref>{{Cite journal|last1=Zorn|first1=Aaron M.|last2=Wells|first2=James M.|date=2009|title=Vertebrate Endoderm Development and Organ Formation|journal=Annual Review of Cell and Developmental Biology|volume=25|pages=221–251|doi=10.1146/annurev.cellbio.042308.113344|issn=1081-0706|pmc=2861293|pmid=19575677}}</ref><ref>{{Cite journal|last1=Nowotschin|first1=Sonja|last2=Hadjantonakis|first2=Anna-Katerina|last3=Campbell|first3=Kyra|date=2019-06-01|title=The endoderm: a divergent cell lineage with many commonalities|journal=Development|language=en|volume=146|issue=11|pages=dev150920|doi=10.1242/dev.150920|issn=0950-1991|pmid=31160415|pmc=6589075}}</ref> 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.<ref name=":1" />

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.<ref>{{Cite web|url=https://embryo.asu.edu/pages/process-eukaryotic-embryonic-development|title=Process of Eukaryotic Embryonic Development {{!}} The Embryo Project Encyclopedia|website=embryo.asu.edu|access-date=2019-11-07}}</ref> 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.<ref>{{Cite journal|last1=Hartenstein|first1=Volker|last2=Stollewerk|first2=Angelika|date=2015-02-23|title=The Evolution of Early Neurogenesis|journal=Developmental Cell|volume=32|issue=4|pages=390–407|doi=10.1016/j.devcel.2015.02.004|pmid=25710527|pmc=5987553|issn=1534-5807}}</ref>

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,<ref>{{Cite web|url=https://www.medicinenet.com/embryo_vs_fetus_differences_week-by-week/article.htm|title=Embryo vs. Fetus: The First 27 Weeks of Pregnancy|website=MedicineNet|language=en|access-date=2019-11-07}}</ref> whereas in [[Biology:Zebrafish|zebrafish]], embryonic development is considered finished when a bone called the [[Biology:Cleithrum|cleithrum]] becomes visible.<ref>{{Cite journal|last1=Kimmel|first1=Charles B.|last2=Ballard|first2=William W.|last3=Kimmel|first3=Seth R.|last4=Ullmann|first4=Bonnie|last5=Schilling|first5=Thomas F.|s2cid=19327966|date=1995|title=Stages of embryonic development of the zebrafish|journal=Developmental Dynamics|language=en|volume=203|issue=3|pages=253–310|doi=10.1002/aja.1002030302|pmid=8589427|issn=1097-0177|doi-access=free}}</ref> 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 viviparous 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 [[Biology:Embryology|embryology]] broadly as the study of the development of animals.<ref name=":1" />

===Plant embryos===
{{Main|Biology:Plant embryonic development}}
{{further|Biology:Sporophyte}}
[[File:Ginkgo embryo and gametophyte.jpg|thumb|The inside of a ''[[Biology:Ginkgo|Ginkgo]]'' seed, showing the embryo]]
Flowering plants ([[Biology:Flowering plant|angiosperms]]) create embryos after the fertilization of a haploid [[Biology:Ovule|ovule]] by [[Biology:Pollen|pollen]]. The DNA from the ovule and pollen combine to form a diploid, single-cell zygote that will develop into an embryo.<ref>{{Cite web|url=https://www.britannica.com/science/seed-plant-reproductive-part|title=seed {{!}} Form, Function, Dispersal, & Germination|website=Encyclopedia Britannica|language=en|access-date=2019-11-09}}</ref> The zygote, which will divide multiple times as it progresses throughout embryonic development, is one part of a [[Biology:Seed|seed]]. Other seed components include the [[Biology:Endosperm|endosperm]], 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 [[Biology:Asymmetric cell division|asymmetric]], resulting in an embryo with one small cell (the apical cell) and one large cell (the basal cell).<ref name=":02">{{Cite web|url=http://biology.kenyon.edu/courses/biol114/Chap12/Chapter_12A.html|title=Chapter 12A. Plant Development|website=biology.kenyon.edu|access-date=2019-11-09}}</ref> The small, apical cell will eventually give rise to most of the structures of the mature plant, such as the stem, leaves, and roots.<ref>{{Cite journal|last1=Hove|first1=Colette A. ten|last2=Lu|first2=Kuan-Ju|last3=Weijers|first3=Dolf|date=2015-02-01|title=Building a plant: cell fate specification in the early Arabidopsis embryo|journal=Development|language=en|volume=142|issue=3|pages=420–430|doi=10.1242/dev.111500|issn=0950-1991|pmid=25605778|doi-access=free}}</ref> The larger basal cell will give rise to the suspensor, which connects the embryo to the endosperm so that nutrients can pass between them.<ref name=":02" /> 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.<ref name=":02" /> The dermal tissue will give rise to the [[Biology:Epidermis (botany)|epidermis]] or outer covering of a plant,<ref>{{Cite web|url=https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/13.23/|title={{!}} CK-12 Foundation|website=www.ck12.org|access-date=2019-11-09}}</ref> ground tissue will give rise to inner plant material that functions in [[Earth:Photosynthesis|photosynthesis]], resource storage, and physical support,<ref>{{Cite web|url=https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookglossG.html#ground%20system|title=GLOSSARY G|website=www2.estrellamountain.edu|access-date=2019-11-09|archive-date=2022-06-14|archive-url=https://web.archive.org/web/20220614073946/https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookglossG.html#ground%20system|url-status=dead}}</ref> and vascular tissue will give rise to connective tissue like the [[Biology:Xylem|xylem]] and [[Biology:Phloem|phloem]] that transport fluid, nutrients, and minerals throughout the plant.<ref>{{Cite web|url=https://biologydictionary.net/vascular-tissue/|title=Vascular Tissue|date=2018-05-21|website=Biology Dictionary|language=en-US|access-date=2019-11-09}}</ref> In heart stage, one or two [[Biology:Cotyledon|cotyledon]]s (embryonic leaves) will form. [[Biology:Meristem|Meristem]]s (centers of [[Biology:Stem cell|stem cell]] activity) develop during the torpedo stage, and will eventually produce many of the mature tissues of the adult plant throughout its life.<ref name=":02" /> At the end of embryonic growth, the seed will usually go dormant until germination.<ref>{{Cite journal|last=Penfield|first=Steven|date=2017-09-11|title=Seed dormancy and germination|journal=Current Biology|language=en|volume=27|issue=17|pages=R874–R878|doi=10.1016/j.cub.2017.05.050|issn=0960-9822|pmid=28898656|doi-access=free}}</ref> Once the embryo begins to [[Biology:Germination|germinate]] (grow out from the seed) and forms its first true leaf, it is called a [[Biology:Seedling|seedling]] or plantlet.<ref>{{Cite web|url=https://forages.oregonstate.edu/regrowth/how-does-grass-grow/developmental-phases/vegetative-phase/germination-and-seedling|title=Germination and Seedling Emergence|date=2016-03-28|website=Forage Information System|language=en|access-date=2019-11-09}}</ref>

Plants that produce [[Biology:Spore|spore]]s instead of seeds, like [[Biology:Bryophyte|bryophyte]]s and [[Biology:Fern|fern]]s, also produce embryos. In these plants, the embryo begins its existence attached to the inside of the [[Biology:Archegonium|archegonium]] on a parental [[Biology:Gametophyte|gametophyte]] from which the egg cell was generated.<ref>{{Cite web|url=https://www.anbg.gov.au/bryophyte/life-cycle-in-nutshell.html|title=Life Cycle - in a nutshell - bryophyte|website=www.anbg.gov.au|language=en|access-date=2019-11-14}}</ref> 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.<ref>{{Cite web|url=https://www.britannica.com/science/plant-development|title=Plant development - Nutritional dependence of the embryo|website=Encyclopedia Britannica|language=en|access-date=2019-11-14}}</ref> The structure and development of the rest of the embryo varies by group of plants.<ref>{{Cite journal|url=https://opentextbc.ca/biology2eopenstax/chapter/bryophytes/|title=Bryophytes – Biology 2e|website=opentextbc.ca|date=5 March 2018|access-date=2019-11-14|last1=Clark|first1=Mary Ann|archive-date=2022-05-03|archive-url=https://web.archive.org/web/20220503161011/https://opentextbc.ca/biology2eopenstax/chapter/bryophytes/|url-status=dead}}</ref>

Since all land plants create embryos, they are collectively referred to as [[Biology:Embryophyte|embryophyte]]s (or by their scientific name, Embryophyta). This, along with other characteristics, distinguishes land plants from other types of plants, such as [[Biology:Algae|algae]], which do not produce embryos.<ref>{{Cite web|url=http://formosa.ntm.gov.tw/seaweeds/english/a/a1_01.asp|title=What are seaweeds?|website=formosa.ntm.gov.tw|access-date=2019-11-09|archive-date=2019-11-20|archive-url=https://web.archive.org/web/20191120024418/http://formosa.ntm.gov.tw/seaweeds/english/a/a1_01.asp|url-status=dead}}</ref>

==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 [[Biology:Stem cell|stem cell]]s,<ref>{{Citation|title=Chapter 4 - Of Mice and Men: The History of Embryonic Stem Cells|date=2014-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780124115514000040|work=Stem Cells (Second Edition)|pages=69–100|editor-last=Mummery|editor-first=Christine|publisher=Academic Press|doi=10.1016/B978-0-12-411551-4.00004-0|isbn=9780124115514|access-date=2019-11-14|editor2-last=van de Stolpe|editor2-first=Anja|editor3-last=Roelen|editor3-first=Bernard A. J.|editor4-last=Clevers|editor4-first=Hans}}</ref> [[Biology:Evolutionary developmental biology|evolution and development]],<ref>{{Cite journal|last1=Martín-Durán|first1=José M.|last2=Monjo|first2=Francisco|last3=Romero|first3=Rafael|date=2012|title=Planarian embryology in the era of comparative developmental biology|journal=The International Journal of Developmental Biology|volume=56|issue=1–3|pages=39–48|doi=10.1387/ijdb.113442jm|issn=1696-3547|pmid=22450993|doi-access=free}}</ref> [[Biology:Cell division|cell division]],<ref>{{Cite journal|last1=Kumar|first1=Megha|last2=Pushpa|first2=Kumari|last3=Mylavarapu|first3=Sivaram V. S.|date=July 2015|title=Splitting the cell, building the organism: Mechanisms of cell division in metazoan embryos|journal=IUBMB Life|volume=67|issue=7|pages=575–587|doi=10.1002/iub.1404|issn=1521-6551|pmc=5937677|pmid=26173082}}</ref> and [[Biology:Gene expression|gene expression]].<ref>{{Cite journal|last1=Jukam|first1=David|last2=Shariati|first2=S. Ali M.|last3=Skotheim|first3=Jan M.|date=2017-08-21|title=Zygotic Genome Activation in Vertebrates|journal=Developmental Cell|volume=42|issue=4|pages=316–332|doi=10.1016/j.devcel.2017.07.026|issn=1878-1551|pmc=5714289|pmid=28829942}}</ref> Examples of scientific discoveries made while studying embryos that were awarded the Nobel Prize in Physiology or Medicine include the [[Biology:Spemann-Mangold organizer|Spemann-Mangold organizer]], a group of cells originally discovered in amphibian embryos that give rise to neural tissues,<ref>{{Cite web|url=https://embryo.asu.edu/pages/spemann-mangold-organizer|title=Spemann-Mangold Organizer {{!}} The Embryo Project Encyclopedia|website=embryo.asu.edu|access-date=2019-11-14}}</ref> and genes that give rise to [[Biology:Segmentation|body segments]] discovered in ''[[Biology:Drosophila melanogaster|Drosophila]]'' fly embryos by [[Biography:Christiane Nüsslein-Volhard|Christiane Nüsslein-Volhard]] and [[Biography:Eric F. Wieschaus|Eric Wieschaus]].<ref>{{Cite web|url=https://www.nobelprize.org/prizes/medicine/1995/7713-the-nobel-prize-in-physiology-or-medicine-1995/|title=The Nobel Prize in Physiology or Medicine 1995|website=NobelPrize.org|language=en-US|access-date=2019-11-14}}</ref>

=== Assisted reproductive technology ===
Creating and/or manipulating embryos via [[Engineering:Assisted reproductive technology|assisted reproductive technology]] (ART) is used for addressing fertility concerns in humans and other animals, and for [[Biology:Selective breeding|selective breeding]] in agricultural species. Between the years 1987 and 2015, ART techniques including [[Biology:In vitro fertilisation|in vitro fertilization]] (IVF) were responsible for an estimated one million human births in the United States alone.<ref>{{Cite web|url=https://www.pennmedicine.org/updates/blogs/fertility-blog/2018/march/ivf-by-the-numbers|title=IVF by the Numbers – Penn Medicine|website=www.pennmedicine.org|language=en-US|access-date=2020-04-15}}</ref> Other clinical technologies include [[Medicine:Preimplantation genetic diagnosis|preimplantation genetic diagnosis]] (PGD), which can identify certain serious genetic abnormalities, such as [[Medicine:Aneuploidy|aneuploidy]], prior to selecting embryos for use in IVF.<ref>{{Cite journal|last1=Basille|first1=Claire|last2=Frydman|first2=René|last3=El Aly|first3=Abdelwahab|last4=Hesters|first4=Laetitia|last5=Fanchin|first5=Renato|last6=Tachdjian|first6=Gérard|last7=Steffann|first7=Julie|last8=LeLorc'h|first8=Marc|last9=Achour-Frydman|first9=Nelly|date=July 2009|title=Preimplantation genetic diagnosis: state of the art|journal=European Journal of Obstetrics, Gynecology, and Reproductive Biology|volume=145|issue=1|pages=9–13|doi=10.1016/j.ejogrb.2009.04.004|issn=1872-7654|pmid=19411132}}</ref> Some have proposed (or even attempted - see [[Biography:He Jiankui affair|He Jiankui affair]]) [[Biology:Genetic engineering|genetic editing]] of human embryos via CRISPR-Cas9 as a potential avenue for preventing disease;<ref>{{Cite web|url=https://www.npr.org/sections/health-shots/2019/02/01/689623550/new-u-s-experiments-aim-to-create-gene-edited-human-embryos|title=New U.S. Experiments Aim To Create Gene-Edited Human Embryos|website=NPR.org|language=en|access-date=2020-04-15}}</ref> however, this has been met with widespread condemnation from the scientific community.<ref>{{Cite journal|last1=Cyranoski|first1=David|last2=Ledford|first2=Heidi|date=2018-11-26|title=Genome-edited baby claim provokes international outcry|journal=Nature|language=en|volume=563|issue=7733|pages=607–608|doi=10.1038/d41586-018-07545-0|pmid=30482929|bibcode=2018Natur.563..607C|s2cid=53768039|doi-access=free}}</ref><ref>{{Cite magazine|url=https://time.com/5550654/crispr-gene-editing-human-embryos-ban/|title=Experts Are Calling for a Ban on Gene Editing of Human Embryos. Here's Why They're Worried|magazine=Time|language=en|access-date=2020-04-15}}</ref>

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.<ref>{{Cite journal|last=Blondin|first=P.|date=January 2016|title=Logistics of large scale commercial IVF embryo production|journal=Reproduction, Fertility, and Development|volume=29|issue=1|pages=32–36|doi=10.1071/RD16317|issn=1031-3613|pmid=28278791}}</ref> 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.<ref>{{Cite web|url=https://ag4impact.org/sid/genetic-intensification/livestock-breeding/embryo-transfer/|title=Agriculture for Impact Embryo Transfer|language=en-US|access-date=2020-04-15|archive-date=2020-07-31|archive-url=https://web.archive.org/web/20200731013759/https://ag4impact.org/sid/genetic-intensification/livestock-breeding/embryo-transfer/|url-status=dead}}</ref> IVF and other ART techniques, including [[Biology:Cloning|cloning]] via interspecies somatic cell nuclear transfer (iSCNT),<ref>{{Cite book|last=Fletcher|first=Amy Lynn|title=Mendel's Ark|chapter=Bio-Interventions: Cloning Endangered Species as Wildlife Conservation|date=2014|work=Mendel's Ark: Biotechnology and the Future of Extinction|pages=49–66|editor-last=Fletcher|editor-first=Amy Lynn|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-017-9121-2_4|isbn=978-94-017-9121-2}}</ref> are also used in attempts to increase the numbers of endangered or vulnerable species, such as Northern white rhinos,<ref>{{Cite news|first=Ian |last=Sample |url=https://www.theguardian.com/environment/2019/sep/11/scientists-use-ivf-procedures-to-help-save-near-extinct-rhinos|title=Scientists use IVF procedures to help save near-extinct rhinos|date=2019-09-11|work=The Guardian|access-date=2020-04-15|language=en-GB|issn=0261-3077}}</ref> [[Biology:Cheetah|cheetah]]s,<ref>{{Cite web|url=https://www.cnn.com/2020/02/24/us/cheetah-cubs-ivf-scn-trnd/index.html|title=Two cheetah cubs were born for the first time by IVF. The breakthrough offers hope for the threatened species|first=Alicia |last=Lee|website=CNN|date=25 February 2020 |access-date=2020-04-15}}</ref> and [[Biology:Sturgeon|sturgeon]]s.<ref>{{Cite journal|last1=Fatira|first1=Effrosyni|last2=Havelka|first2=Miloš|last3=Labbé|first3=Catherine|last4=Depincé|first4=Alexandra|last5=Iegorova|first5=Viktoriia|last6=Pšenička|first6=Martin|last7=Saito|first7=Taiju|date=2018-04-16|title=Application of interspecific Somatic Cell Nuclear Transfer (iSCNT) in sturgeons and an unexpectedly produced gynogenetic sterlet with homozygous quadruple haploid|journal=Scientific Reports|language=en|volume=8|issue=1|pages=5997|doi=10.1038/s41598-018-24376-1|pmid=29662093|pmc=5902484|bibcode=2018NatSR...8.5997F|issn=2045-2322}}</ref>

=== Cryoconservation of plant and animal biodiversity ===
[[Biology:Cryoconservation of animal genetic resources|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.<ref>{{Cite web|url=http://www.fao.org/3/a0399e/A0399E06.htm|title=The Role of Biotechnology in Exploring and Protecting Agricultural Genetic Resources|website=www.fao.org|access-date=2020-04-15}}</ref> Some large-scale animal species cryoconservation efforts include "[[Biology:Frozen zoo|frozen zoo]]s" in various places around the world, including in the UK's [[Biology:Frozen Ark|Frozen Ark]],<ref>{{Cite web|url=https://www.frozenark.org/|title=Frozen Ark}}</ref> the Breeding Centre for Endangered Arabian Wildlife (BCEAW) in the United Arab Emirates,<ref>{{Cite web|url=http://www.bceaw.ae/|title=Breeding Centre for Endangered Arabian Wildlife|website=www.bceaw.ae|access-date=2020-04-15}}</ref> and the San Diego Zoo Institute for Conservation in the United States.<ref>{{Cite web|url=https://institute.sandiegozoo.org/resources/frozen-zoo%C2%AE|title=Frozen Zoo®|date=2016-01-26|website=San Diego Zoo Institute for Conservation Research|language=en|access-date=2020-04-15}}</ref><ref>{{Cite web|url=https://www.smithsonianmag.com/science-nature/san-diegos-frozen-zoo-180971276/|title=San Diego's Frozen Zoo Offers Hope for Endangered Species Around the World|website=Smithsonian Magazine|language=en|access-date=2020-04-15}}</ref> 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.<ref>{{Cite web|url=http://www.independent.co.uk/life-style/gadgets-and-tech/features/seed-vault-doomsday-svalbard-norway-milennium-kew-biodiversity-bank-gene-a8237221.html|title=A vast crypt was built to protect humans from the apocalypse. But doomsday might already be here|date=2018-03-04|website=The Independent|language=en|access-date=2020-04-15}}</ref> The [[Biology:Svalbard Global Seed Vault|Svalbard Global Seed Vault]] in Norway maintains the largest collection of plant reproductive tissue, with more than a million samples stored at {{cvt|-18|C}}.<ref>{{Cite web|url=https://www.croptrust.org/our-work/svalbard-global-seed-vault/|title=Svalbard Global Seed Vault|website=Crop Trust|language=en-US|access-date=2020-04-15}}</ref>

==Fossilized embryos==

Fossilized animal embryos are known from the [[Earth:Precambrian|Precambrian]], and are found in great numbers during the [[Earth:Cambrian|Cambrian]] period. Even fossilized [[Biology:Dinosaur|dinosaur]] embryos have been discovered.<ref>{{cite news | url=https://www.bbc.com/news/science-environment-22085535 | title=Dinosaur embryo fossils reveal life inside the egg | work=BBC News | access-date=8 August 2015 | author=Morelle, Rebecca |  url-status=live | archive-url=https://web.archive.org/web/20150924135744/http://www.bbc.com/news/science-environment-22085535 | archive-date=24 September 2015 }}</ref>

==See also==
{{cols}}
* [[Biology:Embryo loss|Embryo loss]]
* [[Medicine:Pregnancy|Pregnancy]]
* [[Biology:Prenatal development|Prenatal development]]
* [[Biology:In vitro fertilisation|In vitro fertilisation]]
* [[Biology:Pre-embryo|Pre-embryo]]
* [[Medicine:Miscarriage|Miscarriage]]
* [[Medicine:Abortion|Abortion]]
{{colend}}

==Notes==
{{Reflist}}

==External links==
* [http://php.med.unsw.edu.au/embryology/index.php?title=Main_Page UNSW Embryology - Educational website]
* [https://web.archive.org/web/20060206140431/http://raven.zoology.washington.edu/embryos/ A Comparative Embryology Gallery]

{{s-start}}
{{s-bef|before=[[Biology:Zygote|Zygote]]}}
{{s-ttl|title=[[Biology:Developmental biology|Animal development]]|years=Embryo}}
{{s-aft|after=[[Biology:Fetus|Fetus]], [[Biology:Hatchling|Hatchling]], [[Biology:Larva|Larva]]}}
{{s-end}}
{{Botany}}
{{Embryology}}

[[Category:Embryology| ]]
[[Category:Developmental biology]]
[[Category:Bioethics]]
[[Category:Fertility medicine]]

{{Sourceattribution|Embryo}}