Development I

Question 1

development

Answer 1

all changes that ocur during entire life cycle of ind; model orgs - spp chosen for research bc easy to study and maintain (ex: sea urchin, frog, chick, nematode)

Question 2

fertilization

Answer 2

sperm (flagellum, small) + egg (larger, non motile); zygot is fert egg (single cell)

Question 3

consequences of fert

Answer 3

restore diploid number (2n); determines sex; activates egg to stimulate rxns and begin development

Question 4

egg

Answer 4

surrounded by plasma mem; one or more coverings depending on spp

Question 5

egg covering

Answer 5

aid in sperm fert of some sp sperm; barrier to interspecific fert; ony same sp sperm gets into fert

Question 6

steps of fert

Answer 6

(1) sperm dissolves protective layers around egg (need to get to PM) (2) molecules on sperm surface bind to receptors on egg surface = recognition (3) upon recog and fert surface of egg changes (4) prevents polyspermy

Question 7

polyspermy

Answer 7

many sperm getting into one egg

Question 8

sea urchine fert steps

Answer 8

(1) jellly coat of eggs releases chems into water (2) attracts sperm via chemotaxis (3) sperm + jelly coat = acrosomal rxn (4) sperm + egg recog causes PM fusion = plasmogamy (sperm nuc enters egg (5a) fast block to polyspermy (5b) slow block to polyspermy via cortical rxn

Question 9

acrosomal rxn

Answer 9

head of sperm (acrosome) releases hydrolytic enx to partially digest jelly coat; acrosomal process forms lock and key mech; sperm head produces actin filament structure that penetrates coat; pserm protein moelcules bind to PM receptors to ensure intraspecific fert

Question 10

sea urchine egg structure

Answer 10

intermost = plasma mem; vitelline layer (thin); outermost = jelly coat (thick layer to glycoproteins for recog)

Question 11

advantages of observing sea urchine fert

Answer 11

readily available; easy to work w; lots of gametes; external fert so can view all steps

Question 12

fast block to polyspermy (in sea urchines)

Answer 12

unfert egg = polarized and cytoplasm is neg charged; w/i secs egg PM ion channels open; NA+ ions rush in and cuase egg depolarization (1-3 sec after binding); prevents fusion w any other sperm bc of depolarized egg; transient bc only lasts approx 1 min

Question 13

slow block to polyspermy (in sea urchines) via cortical rxn

Answer 13

sperm + egg starts diff signal transduction; Ca+ ions released from ER to cytoplasm; tiggers cotical granules formation; vessicles go to egg cortex beneath PM; release conents (enz, macromolecules); fills up (blacks) space btwn VL + PM of egg; cortical rxn; VL hardens, produces fert envelope, prevents sperm entry; cortical granules enz degrade all eg mem receptors; creates complete blcok, irreversible/permanent (takes about 1 min to set up)

Question 14

mammal fert

Answer 14

egg structure: plasma mem, zona pellucida, follicle cells; internal fert; no fast block to polyspermy

Question 15

mammal fert steps

Answer 15

(1) acrosomal rxn: spemr binds to ZP3 glycoprotein receptor on ZP (2) acrosome bursts, releases hydrolytic enz, digest through ZP (3) slow block to polyspermy via cortical rxn (4) Ca+ released into cytoplasm, creates granules (5) release contents at ZP (6) ZP changes - hardens, sperm receptors altered to prevent binding, no fert env formation

Question 16

fert completetion

Answer 16

egg activation; fusion of sperm and egg nuclei (same time as egg act); end of fert = 1st zyote division

Question 17

egg activation

Answer 17

series of metabolic rxns that start + speed up to begin embryonic dev; tiggered by Ca+ inc in cytoplasm: form cortical rxn, maternal enz + proteins activated, inc protein syn of maternal mRNA

Question 18

fusion of sperm + egg nuclei (same time as egg act)

Answer 18

egg dev: sea urchine meiosis completed at time of release, human egg (secondary oocyte) at metaphase II finishes meiosis at meiosis and produces egg nuc and polar body; sperm nuc (n) guided to egg nuc (n) via microtubules, fusion = karyogamy, 20 mins after sperm entry to egg in sea urchins, serveral hrs after sperm entry to egg in humans

Question 19

end of fert

Answer 19

1st zygote divisions; sea urch = about 90 mins after sperm bind egg; humans = about 12-36 hrs after sperm binds egg

Question 20

cleavage

Answer 20

series of rapid mitotic divisions; clevage cell cycle; cleavage furrow; patterm of divison affected by yolk presence

Question 21

clevage cell cycle

Answer 21

mainly S&M phases; syn and mitosis; no G1/G2 phases, no protein syn, no “growth” of cell size; inc cell number w smaller cell size afer each division, embryo size stays small; each new cell = blastomere

Question 22

clevage furrow

Answer 22

indentation in cell surface after cytokinesis

Question 23

clevage and yolk presence

Answer 23

yolk = proteins, fats, phospholipids; depends on spp + embryo needs

Question 24

stages of cleavage

Answer 24

zygote (1 cell) undergos clevage to become embryo (2+ cells); humans = first cleavage 24 hrs after sperm binds, lots of division after to form blastula, at least 128 cells is blastomere, forms hollow ball inside is blastocoel (fluid filled cavity)

Question 25

cleavage in sea urch

Answer 25

deuterostomes: radial, indet; uniforms cleavage across embryo bc all cells are dividing the same way

Question 26

cleavage in frogs

Answer 26

asymmetric cleavage = no uniform bc of yolk dist, most of yolk at one poll of egg; holoblastic cleavage; first 2 furrows form parallel to meridian; 4 blastomeres produced = equal size, from animal to vegetal pole

Question 27

vegetal pole

Answer 27

poll of egg w most yolk

Question 28

animal poll

Answer 28

opposite vegetal poll

Question 29

holoblastic cleavage

Answer 29

yolk = thick composition; slows down cytokinesis completeion at vegetal pole; cleavage furrow (indenp) still passes through entire egg; cleav furrow passes entirely through egg

Question 30

1st cleavage in frogs

Answer 30

furrow will still be trying to divide yolky cytoplasm even through 2nd division has already begun

Question 31

grey crescent in frogs

Answer 31

in first 2 cleavages in frogs; lightered coored region opposite site of sperm entry; gastrulation begins here

Question 32

subsequent divisions in frgos

Answer 32

yok continues to push cleavage toward aniaml pole; blastocoel forms completely at animal hemisphere

Question 33

3rd division in frogs

Answer 33

yolk begins to effect size of cells at 2 polls; equatorial plant perpen meridan; produce 8 cell embryo; yolk near begetal pole displaces mitotic apparatus thus cleavage furrow to animal pole; 2 “tiers” of blastomere that are small at animal pole/hemisphere (more divisions)

Question 34

cleavage in echinoderm, mammals, annelids

Answer 34

relatively little amnt of yolk; holoblastic cleavage; similar sized blastomeres; central bastocoel formation

Question 35

cleavage in birds, reptiles, fish, insects

Answer 35

lots of yolk; cleavage furrow can pass entirely through egg; meroblastic cleavage

Question 36

meroblastic cleavage

Answer 36

“partial”; only region w/o yolk undergoes cleavage

Question 37

newly fert egg

Answer 37

single nuc; little DNA = not enough mRNA to meet all of cell’s need for protein

Question 38

inital dev

Answer 38

carried out by maternal mRNA (proteins from oogenesis)

Question 39

after cleavages

Answer 39

many blastomeres; many nuclei; lots of DNA; small cells w neough DNA + mRNA to support their needs