tim boswell material Flashcards
discuss preformation and epigenesis explanations of animal development
preformation thwory is that the sperm contains a tiny human creature (homunculus) that simply gets bigger over time
epigenesis is the idea that new bodily structures arise over time
who theorised cell theory
schleiden and schwann
how do epithelial tubes form
epithelial cells tighten their ‘adhesion belt’ of actin filaments which causes invagination of the epithelial sheet
what is the pattern formation principle
the idea that cells become organised spatially and are given information about what to become
describe what bodily structures the three germ layers go on to become
endoderm; gut, liver and lungs
mesoderm; skeleton, muscles, blood vessels
ectoderm; skin, nervous system
discuss the two explanations of detemination (even though development probobly consists of parts of both)
mosaic development; chemicals and other determinants are distributed throughout cells unequally
regulative development; cell to cell communication and environmental signals determine fate
discuss evidence for mosaic and regulative development/determination
mosaic; if a 2-cell frog embryo has 1 cell destroyed, then only half an embryo develops
regulative; removing parts of an embryo often still leads to normal development
when a sea urchin embryo is rearranged, normal development still occours
what is the name of the two poles
name which one is on top/bottom
which pole develops quicker and therefore cosnsists of more cells but smaller ones
animal pole (top) vegetal pole (bottom)
the animal pole divides quicker
which embryo pole consists of much cytoplasm and little yolk, which is the orther way around
animal pole has much cytoplasm, little yolk
vegetal pole has much yolk, little cytoplasm
define holoblastic and meroblastic cleavage
complete cleavage
most protostomes and deuterostomes
incomplete cleavage; only superficial cleavage occours forming a cytoplasmic mass containg several nuclei (synctium)
discuss spiral and radial cleavage,
state if they perform holoblastic or mesoblastic cleavege
which method is used by protostomes and deutrrostomes
both are holoblastic (complete division)
radial; upper tier directly above lower tier
deuterostomes
equal yolk division between both poles
spiral; upper tier in between lower tiers
protostomes
yolk concentrated in one hemisphere (vegetal)
when do the animal and vegetal hemispheres develop
after cleavage (holoblastic/meroblastic methods)
when is embryo bilateral symmetry established rather aswell as radial symmetry
when the cells have cleaved and arrange into poles
which pole and hemisphere in an animal embryo contains dense yolk and which doesnt contain yolk
vegetal pole is yolky, animal pole has no yolk
which group of animals display a grey crescent and why do they display it
amphibians;
animal pole is pigmented and vegetal pole isint so when the cortical cytoplasm roates realtive to the inner cytoplasm a colour change occors
discuss the events that occour in tunicate eggs after fertilisation
cortical cytoplasm (yellow) moves to the vegatal pole and forms a crescent which then goes on to form muscle tissue due to this cytoplasm containing mRNA for macho1 transcription factor which switches on genes for muscle development
why does tunicate muscle development sopport mosaic development
the yellow cytoplasm at the vegetal pole forms muscle tissue due to the fact it contians mRNA for macho1 TF. sopports the idea of cytoplasmic determinants
which species (common name) is a model organisms for developmental work concerning organ development and apoptosis
why is this organism used
c. elegans (nematode worm)
embryogenesis only takes 15 hours
how many somatic cells does the nematode worm have. how mnay die during development
- 131
in the nematode worm, there is evidence for both mosaic and regulative development; discuss
mosaic; only the cells containg P granules (RNA and cytoplasm) becomes germ cells
regulative; moving the position of cells results in upside down development (normal development)
what is another name for a sea urchin
echinoderm
what is another name for an echinoderm
sea urchin
why are sea urchin eggs used to embryo development
many eggs produced by animal and released into water
eggs are easy to fertilise and observe because they’re transparent
what is a blastula and a blastocoel
a blastula is the hollow ball of cells that exists before gastrulation occours
a blastocoel is the fluid filled cavity in the blastula
name the animal whos gastrulation was studied and then describe that gastrulation
sea urchin(echinoderm). posterior cell change shape and become the archenteron, some cells break off and become primary mesenchyme, some cells break off and attach themselves to both the roof of the embryo and the roof of the archenteron (secondary mesenchyme). the secondary mesenchyme have filament projections called filopodia which they contract to pull the archenteron through the embryo, forming a tube which eventually become the gut.
the blastopore is the end of the hole first created
do echinoderms perform radial or spiral cleavage
radial cleavege; they are deuterostomes
the first opening (blastopore) to the gut always becomes the XXXX in deuterostomes
anus
what is important about the fourth wave of divisiion in echinoderms
the animal pole cells becomes smaller than the vegetal pole
tiny cells called micromeres form below the vegetal pole
give an example of mosaic development in echinoderms
there is a level of predictability concerning which parts of the cytoplasm will become which germ layer, therefore there must be some internal programming
in terms of echinoderm embryos;
wat would have if a 4 cell embryo is split into 4 cells, and why?
what would happen if the 8 cell embryo is split vertically and why?
what would happen if the animal hemisphere and 1 micromemre, and why?
what happens when the animal hemisphere and 4 micromeres are combined without vegetal pole, and why?
what would happen if the animal pole a set of micromeres at each pole were combined and why?
4 cell; 4 normal larvas develop (regulative)
8 cell; an animalised larva and a vegetalised larva would develop because the animal and vegetal pole have already developed (mosaic). the animal larva has ectodderm and the vegetalised larva has endoderm
animal hemisphere and 1 micromere; animalised larva
animal hemisphere and 4 micromeres; normal larva;
animal hemisphere and 8 micromeres; 2 archenteron, 2 blastopore etc
discuss what micromeres are why they are important
they are 4 tiny cells underneath the vegetal pole which have been shown to be key to development. they are thought to contribute to the concentration gradients in the embryo that gives cells positional information key to pattern formation. may contain high concentrations of morphogens (gradient theory of development)
what is the gradient theory and what evidence is there for it
the idea that concentration gradients of important chemicals are what lead to development. dyes were added to embryos and it was revealed that a lot of metabolic activity occours at the two poles of the embryo and that morphogens are at high concentrations at embryo poles
what is the french flag model and who theorised it
Wolpert
every cell has the potentiol to become any other cell; it is the concentration of morphogens that determines cell fate. a threshold of chemical needs to be exceeded for a cell to be determined
what is a GRN theory?
who worked on GRN’s?
which animal did he investigate them in??
gene regulatory network. the idea that development is controlled by regulation of genes (kernals) and that each cell expressed different regulatory DNA
Davidson
Echinoderms
what are insulators
cis regulatory elements that block the action of enhancers
what are the effects if one gene mutates in a kernal
the kernal may not funciton which may have massive developmental effects
discuss the GRN for beta catenin
in the animal pole, no beta catenin is present so a repressor is transcribed which blocks genes neeeded for vegetal development (tbr, delta, ets, dri)
maternal beta catenin and otx mRNA are deposited in the micromeres and Veg2 layers;
expression of beta-catenin and otx as transcription factors ococur, which activates transcription of gene (pmar1) which inhibits the expression of a gene that would normally repress expression of genes needed for vegetal development (gastrulation and skeleton development)
what is gametogenesis and how is done
formation of haploid cells (gametes) by meiosis
spermatogenesis
oogenesis
what is the scientific name for a mature egg cell and what cell pathway leads to it
a mature egg cell is called an ovum.
a diploid precursor cell (oogonia) becomes a primary oocyte (diploid) which becomes a mature ovum (haploid) bia meiosis
what is vitellogenesis, when does it occour and how long does it take
vitellogenesis is the increases in size and storage of nutrients that occours during oogenesis (egg formation). it takes place during an extended prophase which may take months/years
describe the features of a mature egg (ovum)
1) presence of yolk (either lots/not much)
2) presence of a membrane which thickens upon fertilisation to stop further sperm entry
3) presence of mitochondria, ribosomes and mRNA
what is the molecule contained in yolk
vitellin, a lipoprotein (phospholipid sphere containing lipids)
what are the two ways oogenesis can be classified
relationship of oocyte to other cells
method of yolk synthesis
descibe the 3 different relationships an oocyte can have with other cells during oogenesis and which animals have each pattern
solitary; egg floats in body fluid
polychaeta
association with follicle cells (somatic) which provide physical sopport.
locusts for example have an entire organ (panoistic ovary) full of follicle cells. the oocytes develop in tubes called ovarioles, and is then passes to a tnother tube called the oviduct which is pushed into soil and used to lay eggs
nutrimentary association; oocyte is associated with sister cells called nurse cells in a chamber which is surrounded by follicle cells
drosophila
what are nurse cells derived from and what is their function
nurse cells are derived from oogonia germ cells and their function is provide the oocyte with nutrients and RNA
describe the 2 different ways a oocyte can be catagorised in terms of how it synthesis yolk
autosynthesis; oocyte takes up amino acids and carbohydrates and performs yolk synthesis itself
heterosynthesis; other cells perform yolk synthesis, and proteins like vitellogenin are taken up by the oocyte
what are two pieces of evidence are there sopport the idea that oocytes can perfom heterosynthesis of yolk proteins
identical proteins to those in yolk have been found in body fluid
microscopy shows that vesicular transport occour at oocyte plasma membrane
how are some oocytes able to autosynthesise yolk proteins
because of maternal deposits of amino acids
which animals perform autosynthesis and which perform hetrosynthesis
autosynthesis is done by those who perform solitary oogenesis; polycheate
heterosynthesis is done by those who perform follicular and nutrimentary oogenesis
whcih animal is a model organism of body plan development and how long does full development from a fertilised egg take
drosphila
9 days
which type of cleavage does drosphila perform
merblastic (incomplete cleavage)
discuss the nobel prize winning work of Nusslein-Volhard and Wieschaus
treated drosophila embryos with chemical mutagens and investigated how each gene mutation effected the body plan of the larva
what evidence is there that drosophila cytoplasm have developmental signals in them
if the anterior cytoplasm from a wild type drosophila is placed anteriorlly in a mutated drosophila with no anterior structures (bicoid mutant), then anterior structures will develop
if the cytoplasm is placed in the middle of the mutated drosophila embryo, then anterior head like structures will develop in the middle of the mebryo
what is the name given to a larva with mutaitons meaning no head segments develop
bicoid mutation
summarise how maggots (fly larva) are formed
the mRNA of maternal effect genes is deposited in the oocyte unequally so that when expression occours there in a protein gradient; a cascade of gene activation occurs, (one set of genes activating another causing refinement of pattern formation) with different genes being expressed in different parts of the embryo leading to different structures
name the 5 sets of genes that are involved in drosophila body plan development
maternal effect genes gap genes pair rule genes segment polarity genes segmentation genes selector genes
name the maternal effect genes
name where they are highly concentrated
name what they cause development of and how
bicoid; anterior; morphogen which causes development of anterior structure.
promotes tranlation of hunchback and inhibits translation of caudal (gap genes)
nanos; posterior; promotes translation of caudal and inhibits translation of hunchback
oskar; posterior; linked to nanos
gurken; posterior
where is oskar (maternal mRNA) highly concentration
posterior pole of the drosophila embryo
how to maternal mRNA’s come to be highly concentrated in particular areas of the embryo
the gurken maternal mRNA is translated posteriorly, and attched to the torpedo receptor on the posterior follicle cells, which then signal for cytoskeleton rearrangement, causing maternal mRNA’s to move along the cytoskeleton to where they are known to be highly concentrated
when is a dorsal ventral axis established in drosophila embryo
after the gurken protein has bound to torpedo receptors it moves dorsally and establishes this axis
what causes the nucleus to move dorsally
after the gurken mRNA has been translated and the protein has binded to the torpedo receptor, gurken mRNA moves dorsally and then so does the nucleus
where does drosophila maternal mRNA come from
nurse cells
name one gap gene and 3 genes it represses
hunchback gene expressed anteriorly and represses knirps, kruppel and gianto
what happens when gap genes are mutated
segments are deleted
name the two pair rule genes and what each’s expression leads to
even skipped gene (eve_ leads to development of odd numbered parasegments
fushi tarazu (ftz) leads to development of even numbered parasegments
what does expression of pair rule genes lead to
development of 14 parasegments (precursor segments)
