lecture 1 Flashcards
What is embryogenesis
the formation of a multicellular organism
what are the stages of development after fertilisation
cleavage gastrulation neurulation organogenesis metamorphosis
name the 6 model organism Dale mentioned
Mouse (mus muculus) chick (gallus gallus) Frog (xenopus laevis) Zebrafish (danio rerio) fruitfly (drosophila melanogastor) nematode worm (c. elegans)
what are the HOX genes involved in
Anterior to posterior patterning
what does PAX6 do?
involved in eye development
what is the function of chordin
Neural development
are female gametes formed in meiosis equal?
No. single ovum and two smaller polar bodies
in the amphibian egg what % is yolk protein
90%
What are the 4 Types of egg
Isolecithal
mesolecithal
telolecithal
centrolecithal
which organism forms isolecithal eggs? what are the main features
Mammals and C. elegans. small egg with little yolk evenly distributed throughout cell
which organism form mesolecithal egg
Amphibians. large eggs, large amounts of yolk but only localised to one half of the egg vegetal hemisphere lightly pigment
which organisms form telolecithal eggs
Fish Reptiles Birds. moderate to large amounts of yolk throughout cellexcept at pole
which organisms form centrolecithal eggs
arthropods and insects. yolk concentrated to centre of egg, periphery yolk free
where is the RNA and mRNA in egg synthesised
synthesised by oocyte itself
what are the two hemispheres that make up egg
Animal and vegetal
what is in the animal hemisphere?
presence of egg nucleus- germinal vesicle
whats in vegetal hemisphere
mostly yolk
where do insects hold eggs before ovulation
metaphase 1
where are mammalian eggs held
prophase 1 before ovulation and metaphase 2 II until fertilisation
what is a sperm made up of
Head-haploid nucleus centrosome, acrosome
midpeice- mitochondria, base of flagellum
tail- flagellum
many sperm abnormal (2 heads or 2 tails)
what is parthenogenesis
ability of some species to develop without sperm (some mice have been created -in lab i think)
what are gynomorphs and andromorphs
i dont know
what is a hydatiform mole? and what is it caused by?
when trophoblast cells of placenta form grape like cyst when fertilised. either caused by loss of female chromosome in meiosis or by polyspermy
what is Genetic imprinting?
altering the dna and associated histone protein to only express 1 version of the gene. inactivates other copies
what is parental conflict theory
different imprinting due to interest of each parent in terms of evolutionary fitness
where does the sperm reach the egg
the ampulla region of fallopian tube
what is the egg surrounded by?
in mammals- zona pellucida, in other animals vitelline
what stops cross species fertilisation?
on the outside of the egg is a specific sperm detector (in mice ZP3- without it, infertile)
what causes the acrosome reaction to start?
the sperm coming into contact with zona pellucida
describe the acrosome reaction
enzymes are released from the acrosome that digest a hole in the zona pellucida for sperm to go through. the sperm then fuses with the plasma membrane and increases cytoplasmic Ca2+ which causes the cortical reaction.
what is the cortical reaction?
increased Ca2+ cortical granules bind with plasma membrane and they release their contents into extra cellular space. modifies sperm receptors to prevent poly spermy.
how do other organisms stop polyspermy
many species reverse the charge of the membrane- this is quicker than the cortical reaction
What is Cleavage?
rapid cell division without cell growth, forming progressively smaller blastomeres
what is cytokinesis driven by?
contractile ring of actin and myosin along same equator as the chromosomes line up upon
why does the first cleavage take longest?
because time is needed for the two haploid nuclei to find each other and line up
what are the cleavage rates for several animals
Drosophila: 8mins
C. elegans: 20 -40 mins
Zebrafish: 15-20 mins
Xenopus laevis: 25- 30mins
why is cell cycle so short compared to adults?
cell cycle only includes S and M all gap phases are deleted. S phase is modified so that it is faster
are there gap phases in mammalian cleavage
yes it cell cycle is slower in mammals than other organisms
what controls the cell cycle
the cell cycle is controlled by the ratio of DNA to cytoplasm
what are the two types of cleavage?
holoblastic and meroblastic
what is meant by holoblastic cleavage
found in isolecithal and mesolecithal eggs it is complete cleavage
meroblastic cleavage is…
incomplete cleavage in telolecithal and centrolecithal eggs. only a portion of the egg is cleaved. in insects male sand female nuclei fuse, 9 nuclei are formed after 3 nuclear divisions, move to the edge of cells. memebrane forms
what happens in compaction
outer layer forms epithelium of tropoblast cells. these pump Na+ into extra cellular space in centre of embryo ater follow. blastocoel formed. inner cell mass forms. embryo called a blastocyst
when are gaps added in amphibian cell cycle
at the mid blastula phase
what must happen in order for different cells to be formed
genome must be transcribed.
