zygote neurula

Question 1

Name stages of early embryogenesis

Answer 1

1. zygote
2. cleavage (mitosis)
3. morula
4. blastula (first embryonic cavity)
5. gastrulation (forms germ layers)
6. gastrula (new cavity)
7. organogenesis (neurulation, forms chorda dorsalis, then systems + organs) (vertebrates)

Question 2

what kind of cells made during cleavage

Answer 2

during cleavage, volume of egg cytoplasm is divided into smaller cells called BLASTOMERES

Question 3

what triggers blastomere division. (cleavage)
what is the role of cylin dependant kinases

Answer 3

. activation of mitosis promoting factor (MPF) which is a type of CDK
. regulates the cell cycle of early blastomeres

Question 4

what does initial activation of MPF do

Answer 4

causes alternating M + S phases, no gap phases (G1+G2)

Question 5

is yolk concentration high in the animal pole?
what is yolk rich pole known as

Answer 5

. quite low. cellular divisions faster at animal pole
. vegetal pole

Question 6

what is the purpose of the blastula

Answer 6

. provides first cell layer + cavity (blastocoel) in embryo

Question 7

what is a blastoderm

Answer 7

the wall of the blastula formed from blastomeres

Question 8

role of blastocoel

Answer 8

. provides space for gastrulation cell movements
. prevents premature interactions btw cells with different future development

Question 9

what determines the look of the blastula

Answer 9

pattern of yolk distribution + gradient of some molecules in ooplasm

Question 10

brief expl blastula formation in mammals

Answer 10

. first 2 days, division of cells = 24 hours
. division of mammalian blastomeres = asynchronous (dont happen at same time)
. embryo 16 cells = morula
. in mammals the blastula is called BLASTOCYST

Question 11

why after blastocoel formation in mammals its called blastocyst not blastula

Answer 11

blastula - all of it is part if the embryo
in mammlas, only some cells form embryo, others form foetal part of placenta + envelopes?

Blastocyst is what implants into uterus
It also has other struxtures like trophoblasts

Question 12

types of cell movement during gastrulation

Answer 12

.Invagination - epithelial cells bends inwards
.Ingression - individual cells leave epithelial sheet + become migrating mesenchyme cells
.Involution - epithelial sheet rolls inward + forms underlying layer
.Epiboly - sheet of cells spread by thinning
.Delamination - one cell layer migrates + develops second layer.

** pg 10 look ppt for pics :)

Question 13

explain diploblastic + triploblastic animals

Answer 13

Diploblastic (radiata) - forms ecto and endoderm
Triploblastic (animals with bilateral body symmetry) - ecto, meso, endoderm

Question 14

protostomes vs deuterostomes

Answer 14

P. mouth then anus, coelom forms from splitting of mesoderm.

D. anus then mouth, coelom forms from mesodermal budding of archenteron (cavity wth 2 openings)

Question 15

what does the neural tube + crest do

Answer 15

gives rise to spinal cord + brain
neural crest cells migrate form tube + forms different cells

Question 16

Neuralation brief expl

Answer 16

*cuboidal cells turn columnar, = thickens ectoderm
*cell adhesion causes edges of the plate fold+ rise to form a tube
*cells at tips of neural folds become neural crest cells (epidermis + n plate can give rise to this)
*somites form pairs flanking neural tube + form segmental pattern in vertebrate embryo

Question 17

explain mosaic development

Answer 17

. fertilised ovum undergoes determinate cleavage
. each blastomere has limited development potency
. blastomere is precursor of specific part of embryo.
. blastomere damage/detruction = defective organism
. this due to ooplasmic segregation of morphogens
* not valid for mammalian eggs

Question 18

what are morphogens

Answer 18

. they direst cell/tissue development
. theyre conc gradients in oocytes = ooplasmic segregation
. blasmomeres get a specific set of them during cleavage
. in early devlpmnt the gradients cause diff cells types in distinct spatial order
.*they act by inducing/maintaining expression of diff tagrget genes
* M are secreted proteins that signal btw cells, TF or small molecules

Question 19

when does ooplasmic segregation finish and what happens next

Answer 19

after sperm egg contact.. provokes movement cortical ooplasm
first cleavage furrow goes through middle of grey crescent therefore first 2 blastomeres equal.
next divisions, blastomeres takes diff cytoplasm (depends on location)
* final ooplasmic segregation forms ant/post + ventral/dorsal axis of symmetry

Question 20

what are presumptive regions

Answer 20

cell groups predetermined for certain cell fate (before differention). determinations of these regions increase during early gastrulation

Question 21

why can amphibian embryos be used to revel things in early embryogenesis

Answer 21

they develop in water so can be experimented at all stages. jelly coat can be removed and microsurgeries easily performed on the eggs so no complicated/expensive tools needed

Question 22

stages of the amphibian embryo

Answer 22

1. first cleavage divides zygote into 2 equal blastomeres ( each takes half whats needed morphogens in correct gradient)

• if first 2 blastomeres split, they’ll become 2 genetically identical normal larvae
• if grey crescent stays in only 1 of them, only that blast becomes normal larva

Question 23

how do you get conjoined twins (gastrula)

Answer 23

if you split the presumptive region into 2, you create 2 organizers in same embryo: 2 sets of neural tubes + notochord created.

Question 24

Why do mammals not need egg yolk

Answer 24

Bc They have placenta

Birds and frogs need lots of yolk since their eggs develop outside body

Question 25

Do fish or amphibians have more yolk?

Answer 25

Fish has more yolk bc they have no larval stage-no metapmorphasis (when egg hatches tiny fish comes out no tadpole etc)

Question 26

What is the result of yolk being evenly distributed in mammals

Answer 26

Mammalian cleavage complete and blastomeres equal size

Question 27

How is a frogs have asymmetrical blastomeres

Answer 27

3rd cleavage furrow =equatorial cleavage delayed in vegetal part of the egg

Question 28

What is the grey crescent

Answer 28

Is a structure of AMPHIBIANS that determines body symmetry

Question 29

How is grey crescent formed in external fertilization of amphibians

Answer 29

• Sperm has to penetrate animal pole as vegetal pole full of yolk
• Sperm carries centrioles which contains microtubules to allow rotation of cortical layer of egg
• Mixes dark and light cytoplasm= grey crescent

Grey crescent is the future dorsal part of embryo, notochord formed. When crescent bisected-we get left+right

Question 30

What chromosomes produce molecules for early embryonic development of amphibian

Answer 30

Lampbrush chromosomes (found in oocytes of animals except mammals)