EMBRYO: WEEK 1 - Summary

WEEK 1

Hippocrates (460-370 BCE):

Preformation
Introduced the idea that there is a joint of two kinds of semen that causes generation, the male’s ejaculate and the female’s menstrual blood.

Aristotle (384-322 BCE):

Epigenesis
Published De Generatione animalium.
Described 2 major patterns of cell division during early development: holoblastic cleavage and meroblastic
Also described the 3 ways animals give birth: oviparity. Viviparity, and ovoviviparity.
Supports epigenesis, believing that the organs of an embryo develops gradually and are not preformed.
Believes that only the male’s semen, ‘seed’, contributes to the formation of the fetus.

Galen (129-circa 200):

Supported the idea of Hippocrates.
Believed that both seeds of male and female are relevant for procreation.
Had a misconception that a female genitalia is just an inverted version of the male’s.

Leonardo da Vinci (1452-1519):

Contributed to the development of embryology through his artistic anatomical studies.
Illustrated how a fetus is formed inside the human uterus through observing a pregnant bicornuate uterus.
His studies has inaccuracies due to his specimen.

Hieronymus Fabricius (1537-1619):

Epigenesis
Published the 1st major publications on comparative embryology, de formato foetu.
His publications included illustrations of embryos and fetuses at different stages.
A student of Gabriele Fallopio.
Bursa fabricius (site of B lymphocyte formation in birds), now known as the cloacal bursa, was named after him.

Gabriele Fallopio (1523-1562):

Epigenesis
Described the uterine tubes, formerly known as the Fallopian tube.

William Harvey (1578-1657):

Epigenesis
Best known for his discovery of blood circulation.
Gave the first detailed investigation of embryology, Exercitationes de generatione animalium.
Challenged Aristotle’s idea, arguing that it was the egg that was fundamental to generation, not the sperm.
He later on concluded that Aristotle was right as he found no semen in the uterus.

Marcello Malpighi (1628-1694):

Supports preformation.
Suggests that the development of an embryo is a mere unfolding of an already mature organism.
His experiments on chick embryos initiated what is considered one of the great debates in embryology: are miniature forms of organisms already present within the egg or sperm? Or are the embryo’s organs gradually formed at each generation?

Jans Swammerdam (1673-1680):

preformation
Concluded that animals came from eggs of the same species as he studied the generation of insects.
After he publicized Historia generalis insectorum, he revolutionized the classifications of insects based on their modes of development which are still in use.

Antonie van Leeuwenhoek (1632-1723):

Supported the spermist idea (preformation)
Known for his exceptional making of microscopes.
Published the first depiction of spermatozoa by keenfully observing it under the microscope.
Observed ‘animalcules’ with tails under the microscope from the semen sample which Johannes Ham gave. He later confirmed it by observing his own.
Believes that sperms were ‘seeds’ and females are mere soils from which the seeds are planted.

Nicolaas Hartsoeker (1656-1725):

Believed in the spermist idea (preformation)
Suggested that a preformed individual exists in the head of the sperm. He calls it ‘Homunculus’ or the tiny man.
His concept of homunculus however, was later exposed to be a hoax.

Regnier de Graaf (1641-1673):

Proposed the idea the ‘egg’ in the testicles becomes fertile through ‘seminal vapors’ which reach the eggs form the uterus through the fallopian tube.

Pierre Maupertuis (1689-1759):

Epigenesis
proposed ideas that preempted the genetic theory of inheritance from his study of the inheritance of genetic traits.

Albrecht von Haller (1708-1777):

Preformation
Bonnet’s contemporary and one of ovism’s greatest champions.
suggested that chick embryos must be created at the same time as the yolk and, despite unfertilised eggs also containing yolk, believed that embryo have existed there prior to fertilization.
observed that the yolk appeared to be attached to the embryonic chick’s small intestine.

Charles Bonnet (1720-1793):

Preformation
published Traite d'insectologie.
provided support to the ovist theory of generation by presenting the parthenogenesis in aphids which could apparently breed for generations despite the absence of males.
he argued that females carry within them an entire future generation in miniature form.
He suggested that future generations pre-existed within the germ-cells, as though it was similar to the Russian Matryoshka dolls, having miniature versions inside another.

Lazzaro Spallanzani (1729-1799):

Prefomation
His experimentations on frogs provided the 1st hard evidence of the sperm’s importance in reproduction
demonstrated that actual physical contact between the egg and the sperm is necessary for embryo development to occur by placing ‘trousers’ made of taffeta on mae frogs.

Kaspar Friedrich Wolff (1734-1794):

Supported epigenesis.
Rejected the theory of preformation and instead revived the theory of epigenesis in his dissertation Theoria generationis during the late 18th century.

Christian Heinrich Pander (1794-1865):

Supports epegenesis.
Pander’s chick embryo studies debunked preformation and introduced induction in organ development.
One of 3 pioneers who revolutionized embryology.

Karl Ernst von Baer (1792-1876):

Supported epigenesis.
Expanded Pander’sidea to all vertebrates, discovering the mammalian egg in 1826. His laws refuted old concepts, emphasizing sequential trait development.
His unlabelled 1828 embryos hinted at a shared vertebrate stage.
One of 3 pioneers who revolutionized embryology.

Heinrich Rathke (1793-1860):

Supported epigenesis.
explored vertebrate system development, describing Rathke’s pouch and detailing structures’ evolution.
One of 3 pioneers who revolutionized embryology.

Rudolph Albert von Kölliker (1817-1905):

Validated the claims of sperm formation and its union to the egg by describing sperm formation in adult testes.

Walter Heape (1855-1919):

Achieved the first successful mammalian embryo transfer by transferring embryos from an Angora rabbit to a foster rabbit of a Belgian line, resulting in the birth of a live offspring.
Heape’s conclusion, that a uterine foster mother does not influence the breed of her foster children, likening her uterus during gestation to a bed of soil with various nutrient constituents, laid the foundation for modern commercial embryo transfer in cattle.

Thomas Hunt Morgan (1866-1945):

Revealed that genes are located on chromosomes, establishing the mechanical foundation of heredity and laying the groundwork for modern genetics.

Robert Briggs (1911- 1983), along with Thomas Joseph King (1921-2000):

Achieved a significant milestone by cloning a frog.
Their method involved transplanting blastula nuclei into enucleated eggs, resulting in the development of normal embryos.
This marked the first successful nuclear transplantation in Metazoans, although it’s important to note that the transplants utilized undifferentiated nuclei.

John Gurdon (1933-):

Extended the Briggs and King.
His seminal 1962 paper described the transplantation of intestinal epithelial cell nuclei from Xenopus tadpoles into enucleated frog eggs, resulting in the development of normal tadpoles.
Gurdon’s success revealed a significant conceptual advance in developmental biology.

Steen Malte Willadsen (1943- ):

achieved sheep cloning through nuclear transfer using cells from early embryos.

Ian Wilmut (1944-2023) and Keith Campbell (1954-2012):

modified the cloning procedure.
Successfully cloned the first mammal with fully differentiated adult mammary cells, Dolly, the Finn Dorset lamb.
This groundbreaking achievement demonstrated that the nucleus of an adult mammalian somatic cell could be reprogrammed to develop an entire organism.