Lecture 14 | Development I

Question 1

What is Development?

Answer 1

All of the changes that occur during the life cycle

Question 2

What are the 2 types of development?

Answer 2

Embryonic
After birth/hatching

Question 3

What are Model Organisms?

Answer 3

Species chosen for research
Easily studied
Geneal example to study processes

ex: developmental events of frogs (similar life cycle to humans, embryonic)

Question 4

What is fertilization?

Answer 4

sperm (usually flagellated, motile) + ovum (large, nonmotile)
both haploid

Question 5

What is the result of fertilization?

Answer 5

Diploid Zygote (2n)
Activates egg, stimulates reactions promoting development

Question 6

True or False: Fertilization determine sex

Answer 6

True; it is the frist step, determines the chromosomes involved in doing so

Question 7

What are the Major Steps in Fertilization?

Answer 7

Sperm dissolves protective layers
Bind to surface receptors (ensure same species)
Change egg surface (prevents polysperm)
Nuclei fuse (ready to start embryonic development)

Question 8

What surrounds the egg?

Answer 8

Plasma Membrane + 1 or more coverings

Question 9

What is the purpose of the egg coverings?

Answer 9

Aid in fertilization (specific receptor proteins)
Barrier to interspecific fertilization (especially important for external fertilization)

latter means prevent fertilization with wrong species

Question 10

What are the egg coverings from inside to out?

Answer 10

Plasma Membrane
Zona Pellucida
Follicle Cells (several layers)

Question 11

Where is the egg fertilized?

Answer 11

Internally

Question 12

What is the Acrosomal Reaction?

Answer 12

1. Sperm pushes through follicle cells, binds to receptor in zona pellucida
2. Acrosome bursts, releasing enzymes
3. Help sperm through zona pellucida
4. Plasmogamy (cytoplasmic fusion)

Question 13

What does the Acrosomal Reaction cause?

Answer 13

Ca^2+ to be released from smooth ER (calcium wave)

Question 14

What are the 3 effects of the Calcium Wave?

Answer 14

1. Triggers Corticol Reaction
2. Egg Activation
3. Complete Meiosis, Fuse Nuclei

Question 15

What is the corticol reaction?

Answer 15

Cortical granules fuse with plasma membrane
Enzymes released, trigger slow block
Blocks polyspermy

Question 16

What is the slow block?

Answer 16

Enzymes catalyze changes in zona pellucida
Zona pellucida hardens
Alters sperm receptors, no more sperm can bind
Blocks polyspermy

Question 17

What is Egg Activation?

Answer 17

Series of metabolic reactions start, accelerate onset of embryonic development
Triggered by Ca^2+ in cytoplasm
Increased respiration (maternal enzymes & proteins activated, increased protein synthesis)

Question 18

How does the egg complete meiosis?

Answer 18

Process begins at same time of activation (2nd degree oocyte was paused at metaphase II)
Calcium triggers complete of meiosis

Question 19

How does the egg complete Karyogamy?

Answer 19

Microtubules guide sperm nucleus to egg nucleus

in humans, occurs several hours after sperm enters egg

Question 20

What is the other characteristic of the resutling diploid zygote?

Answer 20

Totipotent; potential to give rise to all cell types

Question 21

What is the 2nd step in embryonic development?

Answer 21

Cleavage

Question 22

What is Cleavage?

Answer 22

Process by which the zygote becomes a multicellular embryo
Rapid divisions with no growth

sacrifice G1 and G2 (no growth) for just S and M (overall faster)

Question 23

What is the Yolk?

Answer 23

Mixture of proteins, phospholipids, fats
Food for developing embryo
Amount, distrbution varies between animal groups

Question 24

What is the purpose of having varying amounts of yolk and varying its distribution?

Answer 24

Depends on needs of embryo
Little yolk = faster, equal
Lots of yolk = slower, unequal

Question 25

What are the stages during Cleavage?

Answer 25

Zygote - 1 cell Embryo - 2+ cells Blastula - Hollow embryo with blastocoel ## Footnote all same size because cells don't grow in between divisions

Question 26

What are the 3 types of cleavage patterns?

Answer 26

Equal Holoblastic Unequal Holoblastic Meroblastic

Question 27

What is Equal Holoblastic?

Answer 27

Complete division Cells equal in size Central Blastocoel | ex: echinoderms, mammals, annelids

Question 28

What is Unequal Holoblastic?

Answer 28

Complete but asymmetrical cleavage (due to yolk distribution - more but moderate amt) Yolk slows cytokinesis | ex: amphibians

Question 29

What is Meroblastic Cleavage?

Answer 29

Only regions without yolk divide completely (rest doesn't divide, amt and density of yolk cannot divide) | ex: reptiles (including birds), many fish, insects