Topic 16: Development I

Question 1

Define development

Answer 1

all changes in life cycle

Question 2

What does development include?

Answer 2

embryonic development, birth/hatching, metamorphosis, etc.

Question 3

What are model organisms? Examples?

Answer 3

species chosen for research -> easily studied

• sea urchin
• frogs
• chickens
• elegans

Question 4

How does a zygote form?

Answer 4

sperm (n) + egg (n) -> zygote (2n)

Question 5

What are the consequences of fertilization?

Answer 5

restores diploid number
determines sex (sometimes)
sperm contact activates egg-> start development

Question 6

What makes up the external egg structure? What is its purpose?

Answer 6

plasma membrane with 1+ coverings
- aid in fertilization
- barrier to interspecific fertilization
especially important for species with external fertilization

Question 7

What are the steps of fertilization?

Answer 7

1. sperm dissolves protective layers around egg
2. sperm binds to egg surface receptors - ensure same species
3. change to egg surface - prevent plasmogamy

Question 8

Why are echinoderms model research organisms?

Answer 8

readily available
easy to work with
easy to obtain with lots of gametes
external fertilization - easy to observe

Question 9

What makes up the egg coverings in sea urchins from internal to external?

Answer 9

jelly coat
sperm binding receptors
vitelline layer
egg PM

Question 10

What are the steps in sea urchin fertilization?

Answer 10

1. acrosomal reaction
2. fastblock to polyspermy
3. cortical reaction - slow block to polyspermy

Question 11

Describe the external fertilization in sea urchins

Answer 11

gametes released into water

egg jelly coat releases chemicals -> attract sperm (chemeotaxis: movement in response to chemical stimulus)

Question 12

What is the acrosomal reaction? What does it do?

Answer 12

acrosome in sperm head releases hydrolytic enzymes

-> break down jelly coat

Question 13

What does the acrosomal process/filaments do?

Answer 13

bind sperm-binding receptors

Question 14

What does the acrosomal reaction trigger?

Answer 14

plasmogamy - sperm and egg PMs fuse -> sperm nuclus enters egg

Question 15

What are the mechanisms used to prevent polyspermy?

Answer 15

fast block

slow block

Question 16

What happens during fast block?

Answer 16

seconds after membrane fusion: ion channels open in egg PM
-> electric “zap” that repels other sperm on egg surface
-> prevents additional sperm/egg PM fusion
lasts about 1 minute

Question 17

What happens during slow block/ cortical reaction?

Answer 17

vitelline layer separates, hardens
-> fertilization envelope - protective layer
-> complete block - irreversible, permanent
requires 1 minute

Question 18

What do egg coverings from inside to outside consist of in mammals?

Answer 18

follicle cells
zona pellucida
plasma membrane

Question 19

What are the steps in mammal fertilization?

Answer 19

1. acrosomal reaction

2. cortical reaction

Question 20

What happens during acrosomal reaction in mammals?

Answer 20

• the sperm binds receptor in zona pellucida

- acrosome bursts, releases enzymes to help sperm get through zona pellucida

Question 21

What happens during the cortical reaction in mammals?

Answer 21

enzymes catalyze changes in zona pellucida

• > zona pellucida hardens
• > alters sperm receptors so that no sperm can bind

Question 22

Does a fertilization envelope form in mammals?

Answer 22

NO

Question 23

What triggers egg activation?

Answer 23

sperm binding

Question 24

What happens during egg activation?

Answer 24

increased respiration
maternal enzymes and proteins activated
increased protein synthesis

Question 25

What signifies the end of fertilization? What is the next stage?

Answer 25

when zygote undergoes first division

embryo

Question 26

What does totipotent mean?

Answer 26

potential to give rise to all cell types

Question 27

What is cleavage?

Answer 27

when a single cell zygote becomes a multicellular embryo

Question 28

What happens during cleavage?

Answer 28

rapid mitosis
very short
no cell growth

Question 29

What is yolk?

Answer 29

a mixture of proteins, phospholipids, fats

-> food for developing embryo

Question 30

What is at the animal pole?

Answer 30

embryo

Question 31

What is at the vegetal pole?

Answer 31

yolk

Question 32

What is cleavage furrow?

Answer 32

indentation during cytokinesis

Question 33

How does a little yolk affect cleavage?

Answer 33

faster, equal cleavage

Question 34

How does a lot of yolk affect cleavage?

Answer 34

slower, unequal cleavage

Question 35

What type of cleavage does this describe:
- cleavage furrow passes entirely through egg
- equal division of egg cytoplasm -> equal blastomeres
- occurs in species with little yolk
What are some examples?

Answer 35

equal holoblastic

sea urchins, humans

Question 36

What type of cleavage does this describe:
- cleavage furrow passes entirely through egg
- unequal blastomeres
- occurs in species with medium amount of yolk
What are some examples?

Answer 36

unequal holoblastic

amphibians

Question 37

What type of cleavage does this describe:
- cleavage furrow does not pass entirely through egg
only through animal pole
- occurs in species with a lot of yolk
What are some examples?

Answer 37

meroblastic cleavage

reptiles, fish, birds