Lec.1 HISTORY OF EMBRYOLOGY (EMBRYO AGAIN)

Question 1

The study of development from fertilization to birth.

from a fertilized egg until it reaches a point where it resembles its adult spp.

In here, we study the prenatal development of an organism.
prenatal = before birth

Answer 1

e m b r y o l o g y

Question 2

In 250 B.C. he described the different ways that
animals are born: oviparity, viviparity, ovoviviparity

He also made an observation that the embryo develops its organ systems gradually – they are not preformed.

Answer 2

a r i s t o t l e

Question 3

oviparity -
viviparity -
ovoviviparity -

Answer 3

oviparity - from eggs
viviparity - from live birth
ovoviviparity - from eggs hatching inside

Question 4

By 1600, he was one of the first to publish a book for comparative embryology.

He investigated the fetal development of many animals, including man, including the first detailed description of the placenta.

Answer 4

H i e r o n y m u s F a b r i c i u s

Question 5

In 1651, he published a book claiming that all things come from the egg.

It would be more than a century after this before egg cells in mammals were actually discovered.

He discovered blood circulation, disproving the earlier notion that blood becomes flesh as it nears the skin.

chick embryo (the small region of the egg containing the yolk-free cytoplasm that gives rise to the embryo proper).

He was also the first to indicate that blood islands form before the heart does.

Answer 5

W i l l i a m H a r v e y

Question 6

In 1672, he published the first microscopic account of chick development and circulation of blood in the arteries and veins in the yolk.

He also observed that even the unincubated chick egg is considerably structured, leading him to think that a preformed version of the chicken resided in the egg.

Answer 6

M a r c e l l o M a l p i g h i

Question 7

In 1677, he discovered spermatozoa which he initially called animalcules.

He thought the sperm was an animal with a tail (which were also mislabeled by some as parasites, particularly Giardia).

This, along with the discovery of the mammalian egg cell lead to the debate of where does the embryo emerge, the egg or the sperm?

Answer 7

A n t o n V a n L e e u w e n h o e k

Question 8

In 1767, contributed to the evidence of epigenesis. For centuries,

He used the example of a plant root that is able to regenerate a whole new plant if the stem and leaves are removed.

This contrasts the preformation theory which stated that all parts of an organism were already pre-formed.

He applied this research to animals, providing evidence that the development of organs and extremities came from the growth of embryonic layers.

Answer 8

C a s p a r Fr i e d r i c h W o l f f

Question 9

the theory that an embryo develops progressively from an undifferentiated egg cell

Answer 9

epigenesis

Question 10

theory that organisms develop from miniature versions of themselves.

a small version of the adult is already inside the germ cells.

Answer 10

preformation theory

Question 11

In 1817, he discovered the germ layers (ectoderm, mesoderm and endoderm).

germ = from the Latin word germen meaning
arise or sprout.

Answer 11

C h r i s t i a n P a n d e r

Question 12

ectos =
derma =
mesos =
endon =

Answer 12

ectos = outside
derma = skin
mesos = middle
endon = inside

Question 13

Considered as the father of embryology.

In 1827 he discovered the mammalian egg cell by opening a canine Graafian follicle.

After further investigation of embryos, he formulated the “von Baer’s Laws.”

This set of rules describes the general patterns of embryonic development.

Four laws in the development of the embryo

Answer 13

K a r l E r n s t V o n B a e r

Question 14

Four laws in the development of the embryo:

Answer 14

General characteristics develop before the special characteristics.

the less general characteristics are developed, until the most specialized arises.

formed embryo does not converge upon other definite forms, but separates itself from them.

embryo of a higher form never resembles any other form,

Question 15

In 1888, he published his results on experimented 2- and 4-cell frog embryos.

He destroyed one of the blastomeres by puncturing it with a hot needle and observed the development of the remaining blastomere.

He found that the remaining blastomere would develop into a half embryo.

It would follow the same course of development it would have if it were still joined with the other blastomere.

He concluded that blastomeres already have a predetermined fate, meaning they develop mosaically.

Answer 15

W i l h e l m R o u x

Question 16

In 1892, he got a different result than Roux from experimenting on sea urchin embryo.

Using separated cells from early cleavage stage embryos, he demonstrated that each of the cells was able to develop into a small but complete embryo and larva.

Each cell was able to produce an entire embryo when separated from the other cells

In some animals the fate of a cell depends on its interactions with neighboring cells, rather than on what piece of cytoplasm it acquired during cleavage.

If a blastomere is removed from an early embryo, the remaining blastomeres can alter their normal fates so as to compensate for the missing blastomere and produce a complete organism (regulative development).

Answer 16

H a n s A d o l f D r i e s c h

Question 17

In 1893, he proposed that the egg and sperm contributed equally to the developing organism (in terms of chromosomes).

He was ahead of his time as study of genetics still weren’t as common.

He proposed that chromosomes carried the inherited potentials of new organisms.

Answer 17

A u g u s t W e i s m a n n

Question 18

A Nobel Prize awardee in Medicine or Physiology, his research on embryos contributed greatly to the field of experimental embryology.

In 1902, he conducted a similar experiment done by Driesch, this time using vertebrate embryo and concluded the same, if separated at an early stage, the cells can form their own embryos.

In 1928, he conducted the first nuclear transfer experiment, transferring the nucleus of a salamander embryo cell into a cell without a nucleus.

This experiment showed that the nucleus from an
early embryonic cell directs the complete growth of an organism.

believed that a tissue or cluster of cells can “organize” surrounding cells to become a certain part of the mature organism. He suspected that in amphibian embryos, it is found in the dorsal lip

(which will become the notochord = spinal cord)

Answer 18

H a n s S p e m a n n

Question 19

In 1935, he was awarded the Nobel Prize for his discovery (together with ____) of embryonic induction.

They discovered that there is an area in the embryo that, upon transplantation into an indifferent part of a second embryo, can induce secondary embryonic growth.

Answer 19

Hans Spemann and Hilde Mangold

Question 20

They demonstrated that a difference in the chromosomes lead to a difference in the sex of the organism.

This is the first concrete proof that materials (chromosomes) in the nucleus lead to a phenotypical difference between organisms.

Answer 20

E d m u n d W i l s o n

N e t t i e S t e v e n s

Question 21

In the 1950s, they both tested the totipotency of nucleus, particularly the genome.

Their experiment included the transfer of a nucleus from a different species to an enucleated cell of another species.

They utilized Rana pipiens and Rana catesbeiana in their experiment.

They are the first to clone an animal.

Answer 21

R o b e r t B r i g g s

T h o m a s Ki n g

Question 22

ability of a single cell to
give rise to all of the differentiated cell
types that build the conceptus.

Answer 22

totipotency

Question 23

In 1975, he was able to clone a frog using cells collected from its intestine.

His experiment suggested that cells retain all of their genetic material even as they divide and differentiate. This also proved that other cells aside from germ calls can also be used for cloning.

Answer 23

J o h n G u r d o n

Question 24

In 1984, he was the first to clone a mammal.

He used a chemical process to separate one cell from an 8-cell lamb embryo.

He then used a small electrical shock to fuse it to an enucleated egg cell which then started to divide.

By this time, in vitro fertilization (within the glass) techniques had been developed, and they had been used to help couples have babies.

So after a few days, he placed the lamb embryos into the womb of surrogate mother sheep.

The result was the birth of three live lambs.

Answer 24

S t e e n W i l l a d s e n

Question 25

In the 1996, they succeeded in producing lambs following transfer of nuclei of cultured cells, harvested from the inner cell mass, to enucleated eggs.

This experiment showed that cultured cells can supply donor nuclei for cloning by nuclear transfer.

This experiment showed that it might be possible to use such modified cells to create transgenic animals.

In the same year, these scientists were able to create a lamb (Dolly) by transferring the nucleus from an adult sheep’s udder cell into an enucleated egg.

This is the first time a mammal has been cloned using somatic cells.

The egg cell of the host needs to be enucleated so that the genetic instructions from the host will not be followed, instead, the donor’s gene instructions will be constructed.

After insertion of the nucleus from the donor, this renders the egg “equivalent to a fertilized egg” as it now has a diploid nucleus.

Development of the embryo will then proceed.

Answer 25

K e i t h C a m p b e l l

I a n W i l m u t

Question 26

animals that have had a
foreign gene deliberately inserted into
their genome.

Answer 26

transgenic

Question 27

cells that are already
differentiated (diploid).

any cell in the body except germ cells.

Answer 27

somatic cells