Embryology Unit 1

development

slow, gradual process of progressive changes over the course of an organism’s life

embryology

the study of animal development from fertilization to birth

preformationism

the belief that there’s a tiny fully developed human that was given nutrients to grow by egg or sperm

spermism

the belief that sperm has the life source in it

Aristotle

first to describe the reproduction mechanisms of animals, technically the first embryologist

epigenesis

step-wise process of growing into the organism that is born

William Harvey

came up with preformationism, disagreed with Aristotle, said that the egg gives life

how, when

embryology seeks to address not what but — and —

pattern formation

what process control the elaboration of cell-and-tissue type patterns?

differentiation

how can this identical set of genetic instructions generate so many different types of cells?

morphogenesis

how can the growth, migration, and death of individual cells be directed and complex functional structures?

growth

how do our cells know when to stop dividing?

reproduction

how are germ cells set apart and what are the instructions present that allow them to form the next generation?

regeneration

how do stem cells retain the capacity to generate new structures and how we can harness these mechanisms to heal?

environmental integration

how is the development of an organism integrated into the larger context of its habitat?

evolution

how are heritable changed proposed to create new body forms given the constraints of survival?

human development

how do humans develop and why do some not develop as expected?

model organinsms

how do we address the questions of embryology?

fertilization→ cleavage → gastrulation → organogenesis → sexual maturation

timeline of embryogenesis

symmetry

in plant development, as soon as there’s a single division its — is established

gastrulation

the period of cell movements, invagination, involution, ingression, delamination, epiboly, and convergent extension

ectoderm, mesoderm, endoderm

what are the 3 germ layers of humans?

skin, CNS

the ectoderm is the developmental germ layer for the — and —

kidneys, bones

the mesoderm is the developmental germ layer of the CV structures, —, gonads, —, muscles

GI, respiratory

the endoderm is the developmental germ layer of the — and —

find it, move it, lose it

how do we mechanicalistically determine what is happening in an embryo?

lost

a gene is said to be necessary and sufficient if its function is — by removing it and gained by moving it

genetic, exogenous

why study embryology? — cause: malformations, syndromes/ — causes: disruptions in normal growth

phocomelia

drug that had thalidomide and was given to pregnant women for morning sickness, caused over 7000 infants to be born with severe limb malformations

common ancestor

evolutionists believe that conserved developmental mechanisms are seen as evidence for a — —

functions

analogous structures share common —

ancestor

homologous structures are derived from a common ancestor

cell specification

how does 1 cell containing 1 full set of genetic info result in a functional living organism with different cell populations?

totipotent

the most unspecified a single cell can be

differentiation

the generation of specified cell types over time

2, environment, flexibility

there are — types of specification, what a cell would become regardless of — circumstances/changes, cells that have — and can be influenced

determination

the irreversible specification of cell, the point of no return

cytoplasmic determinants

endogenous factors in the cytoplasm of the egg that are received by dividing blastula daughter cells

cytoplasmic determinants, independent, yellow crescent

autonomous specifications is when the — — goes to the different daughter cell, it is — of environmental factors, may exhibit a — — of tunicate

macho

— RNA codes for muscle cell fate

division

plant egg cytoplasm divides asymmetrically, the first cell — sets up major apical-basal axis, conditional specification follows the rest of development

conditional

— specification is when there are factors present in a cell’s environment that influence its fate

juxtacrine, paracrine, mechanical, endocrine

factors involved in conditional specification

it would adapt to its environment, the egg would fill in the gaps

if a cell was moved to a new location in the blastula, what would happen to the cell? to the egg?

August Weismann, germ plasma

1888, proposed autonomous specification, mainly in connection to — —

Wilhelm Roux

tested Weismann’s hypothesis with frogs, concluded that specification is autonomous

Hans Driesch

tested Weismann’s hypothesis with sea urchins and got a different result than Roux, because he couldn’t explain why, he quit science and became a professor of philosophy

detected, replenished

Driesch’s sea urchins developed normally meaning that the remaining cells had — that the neighboring cells were lost, however the remaining cells — the lost cells

potency, fate, critical, location

Driesch came to 3 main conclusions: the prospective — of an isolated blastomere is greater than the prospective —, cell — is critical for normal development, the fate of a nucleus depends solely on its — in the embryo

totipotent

all the cells of the placenta and the embryo

pluripotent

all cells of only the embryo

potency

refers to a cell’s capacity to differentiate into various other cell types

syncytial

a type of specification that the fates of all the cells are determined simultaneously

syncytium

single cytoplasm (cell) containing many nuclei (found primarily in insect development)

presumptive

in syncytium each nucleus is considered a — cell in that the components around it will cellularize and it will be a single cell with a single nucleus

fertilization, nuclei, cytoplasmic determinants

axial gradients in drosophila development: cycles of nuclear division begin soon after —, positioning of — and — — guide each nucleuses eventual cell fate

unified

the drosophila egg isn’t uniform but it is —

syncronously

in the drosophila egg nuclei — divide and migrate to opposite poled based on cytoplasmic determinant gradients

syncytial blastoderm

cellularization begins after cycle 13 is in the — —: each nucleus is enveloped by its own membrane

specification

in the egg nuclei positions must be maintained for eventual —-

morphogen

anterior-posterior — gradients are the form-givers, they are diffusible molecules that can determine cell fate via concentration gradients

microtubule

syncytial nuclear positioning is maintained by — extensions that create an ‘orbit’ around the nucleus

autonomous, mosaic

— specification type that is in most invertebrates, occurs via differential acquisition of certain cytoplasmic molecules present in the egg, results in — development: cells cannot change fate if a blastomere is lost

conditional, rearrangements, interactions

— specification predominates in vertebrates and some invertebrates, position of cells relative to each other is key, massive cell — and migrations prior to or with specification, cells can acquire different functions due to — with neighboring cells

syncytial, autonomous, conditional

— specification is found in most insect classes, specification of body regions by interactions with — regions prior to cellularization of blastoderm, after cellularization, both — and — specification take place