Zygote neurula pt2

Question 1

Explain the experiment that proves cytoplasmic factors in early dorsal blastopore lip organize cell differentiation in amphibian embryos

Answer 1

. donor = early salamander gastrula
. The transplant = patch of tissue from primary invagination that’s the starting point of gastrulation
. The tissue is transplanted onto a receipt embryo at same stage, onto region of ectoderm that becomes epidermis

Question 2

what is the result of this experiment

Answer 2

donor tissue invaginates + form 2nd archenteron, + then 2nd chorda dorsalis, neural tube, somites.
eventually a 2nd embryo forms and joins to host

Question 3

what is regulative development

Answer 3

. fertilized ovum does intermediate cleavage, producing blastomeres that h equal development potencies
. No ooplasmic gradients of morphogens
. Early blastomeres are capable of giving rise to an embryo
. Determination of particular organs + part of embryo is influenced by inductors + intercellular interaction
. damage of cells during early development causes readjustments/substitutions so normal organism is formed
. Regulative developmental mechanisms are switched on also in embryos wth mosaic development.

Question 4

Anamnia vs Amniota

Answer 4

^ water animals
^ eternal fertilisation
^ dvlpmnt cud include larval stge
^ fish, amphibia
* tetrapod terrestial anim
* internal fertilisation
* eggs possess envelopes embryo protection
* extraembryonic membranes
* lack of larval stge
* reptilia, birds, mammals

Question 5

over the oocyte (yolk) theres the albumen (egg white)

Answer 5

yolk sac - ecompasses the yolk + helps embryos use nutrients
Amnion - creates a liquid filled cavity around emb, provides water
Chorion - responsible for gas exchange
Allantois - stores nitrogenous wastes in urea form + can take part in gas exchnge
Resistant shell - provides mechanical protection

Question 6

Bird/Mammalian gastrulation main bits

Answer 6

. Gastrulation starts from primitive streak - Hensons node, midline cells move down to blastocoel
. Early gastrulation - embryo flat disc wth epiblast + hypoblast
. Some cells in blastocoel make the mesoderm
. Other cells stay in layer + make endoderm

Question 7

define terms - isolecithal, holoblastic cleavage, meroblastic cleavage, centrolecithal, telolecithal

Answer 7

1. roughly equal distribution of yolk (in sea urchins)
2. complete cleavge
3. partial cleavage, only some cytoplasm cleaved (insects,fish,reptiles,birds)
4. central yolk (insects)
5. only 1 area is yolk free (birds +fish)

Question 8

what is an example for mosaic development?

Answer 8

Nematodes - fate of each blastomere determined
adult worms hv 959 somatic cells with clear origin

Question 9

example for telolecital eggs

Answer 9

zebrafish eggs - cleavage occurs only in yolk free cytoplasm at animal pole.
these eggs also in birds + reptiles

Question 10

example of mesolecithal eggs

Answer 10

amphibians - ooplasm at animal pole not dense so has fast division there

yolk at vegetal pole slows cleavage.
first cleavage furrow bisects grey cresent

Question 11

where on the egg is the 2nd + 3rd division

Answer 11

2nd - starts at animal region of egg
3rd - displaced towards animal pole

vegetal hemisphere has larger + fewer blastomeres than animal bit

Question 12

how blastocoel formed (pg 41 piccy)

Answer 12

blastula divides rapido
. makes blastocoel
. this prevents communication btw animal +vegetal ectoderm
. blastocoel disappears during gatstrulation
. sperm entrance dtermines ant + post axis in embryo
. invagination begins opposite sperm entrance

Question 13

Amphibian gastrulation explain plese

Answer 13

. one side of blastula,small fold, dorsal lip of blastopore appears
. additional cells roll inward over dorsal lip+ form endo and mesoderm
. cells of animal pole (future ectoderm) changes shape + spread over outer surface
.
. blastopore lip grows on both sides of embryo + when they meet, blastopore forms circle that becomes smaller as ectodermgoes downward
. archenteron begons to form, therfore blastocoel becomes smaller

. late gastulation, endoderm lined archenteron is replaced by blastocoel + 3 germ layers here. blatopore surrounds yolk plug filled cells

Question 14

Frog gastrula

Answer 14

1.ecto + endoderm surround gut (archenteron) + make yolk
2. mesoderm btw them.
3. blastocoel pushed to 1 side by largening archteron + not seen after
4. dorsal lip + blaastopore visible with addition of ventral lip
5. yolk plug is endodermal mass btw dorsal + ventral lips

Question 15

features of amphibian neurula

Answer 15

• mesoderm sivided into 5 regions: lateral plate mesoderm, notochord, paraxial mesoderm, head mesenchyme + intermediate mesoderm.
• archenteron very visible.

Question 16

Why do mammals have regulatory development

Answer 16

The blastomeres not influenced by morphogens as mammal blastomeres have genome even in 2 cell stage