Topic 6: Reproduction and Development, pt 2

Question 1

What are the main 4 steps of embryonic development, define each step

Answer 1

1. Fertilization: fusion of the nuclei of egg and sperm. 2. Cleavage: forms set of cells 3. Gastrulation: rearranging to form germ layers 4. Organogenesis differentiation into different organs

Question 2

What are the 3 ways embryos can develop (difference are in where they develop)

Answer 2

1. Oviparity: development takes place outside of female (in egg) ex: reptiles that lay eggs
2. Oviviparity: embryos develop inside the female, off the egg yolk for nutrition, hatch inside, and then released. ex; most sharks.
3. Viviparity: embryonic development takes place inside the female reproductive tract and is birthed live.

Question 3

Fill in blanks with ploidy of each

Fertilization is the formation of a _ zygote from _ gametes.

Answer 3

diploid zygote, haploid gametes

Question 4

How is it ensured that sperm of the same species penetrates the egg? This also prevents polyspermy (entry of multiple sperm)

Answer 4

Molecules on the sperm bind to receptors on the egg plasma membrane.

Question 5

why are sea urchins the model for studying fertilization

Answer 5

Their gametes are easy to collect because there’s a lot of them and fertlization is external.

Question 6

list the steps of fertilization in order

(the sperm penetrating the egg)

Answer 6

Contact of the sperm and egg’s jelly coat, acrosomal reaction, fusion of the sperm and egg membranes, cortical reaction, fusion of egg and sperm nucleus.

Question 7

Describe what happens when sperm contacts the egg’s jelly coat

Answer 7

This triggers exocytosis of the sperm’s acrosome

(expels its enzymes on the surface of the egg)

Question 8

Desribe the acrosomal reaction

Answer 8

Hydrolytic enzymes are released from the acrosome which dissolve a hole into the jelly coat.

Question 9

what forms the acrosomal process, what happens in this process

(within the acrosomal reaction)

Answer 9

Growing actin filaments form the acrosomal process, which protrudes from the sperm head and penetrates the jelly coat. Proteins on the surface of the acrosomal process bind to the receptors in the egg plasma membrane, (“lock and key” recognition).

This lock and key recognition is important for sperm recognition against other externally fertilzied species

Question 10

What does the fusion of the sperm and egg membranes trigger

Answer 10

Depolarization of the membrane (sodium ions diffuse into the egg cytoplasm, decreasing membrane potential).

Question 11

is fusion and depolarization of the membrane, a fast or slow block to polyspermy? how does it block? how long does it last

Answer 11

This acts as a fast block to polyspermy because decreasing the membrane potential stops other sperm from coming in because then lower potenital in the membrane means they’d have to go high to low against the concentration gradient. It takes 1-3 secs to initiate and lasts 1-2 mins.

Question 12

Describe the Cortical reaction. Is it a fast or slow block to polyspermy?

Answer 12

Cortical granules in the egg fuse with the plasma membrane. Secreted contents clip the sperm-binding receptors off the egg and cause the fertilization envelope to form. It acts as a slow block and is longer lasting.

In terrestrial animals its slower than in sea urchins

Question 13

In sea urchins how long does it take the sperm nucleus to fuse to the egg nucleus, how long does it take for the first cell division.

Answer 13

It takes about 20 mins for the nuclei to fuse, and up to 90 mins for the first cell division of the embryo.

Other species will take longer depending on structure

Question 14

How long does it take for the first cell division post sperm binding in mammals

Answer 14

12-36 hours

Question 15

In terrestrial animals eggs are fertlized internally, what surrounds the egg that the sperm must penetrate to get to the egg

Answer 15

The follicular support cells.

Question 16

what’s the zona pellucida

Answer 16

the extracellular matrix surrounding a mammalian egg.

Question 17

a single 2N nucleus of the fertilized egg doesn’t have enough mRNA to carry out cell functions. What parts of the cell cycle does a fertilized egg lack in cleavage stage

Answer 17

interphase and growth (G) phase

So it just has S (synthesis) and M (mitosis) phase

Question 18

Cleavage

Answer 18

a series of rapid cell divisions without the G1 and G2 phase of the cell cycle.

Question 19

Cleavage splits the cytoplasm of the fertilized egg into many smaller cells called _?

Answer 19

blastomeres

Question 20

Fill in the blanks

The first 5-7 cleavage divisions produce the _, surrounding a fluid-filled _

Answer 20

Blastula (hallow ball of cells), blastocoel (blastulas cavity).

Question 21

Where is the yolk (stored nutrients) located in frog eggs

Answer 21

Concentrated to** the vegetal pole,** opposite the animal pole

assymetric distribution of yolk gives rise to these 2 halves of the egg

(think vegetal like vegetable give nutrients, yolk gives nutrients)

Question 22

fill in the position

first 2 cleavage divisions are _ to the poles of the embryo

Answer 22

parallel (from top to bottom)

Question 23

what direction fill in

Third cleavage division is _

Answer 23

perpendicular (across pole axis), opposite direction of first two divisions.

Question 24

Yolk in the vegetal pole pushes the mitotic apparatus into the animal pole, which results in

Answer 24

smaller blastomeres in the animal pole compared to the vegetal pole what is this called

Question 25

Holoblastic

Answer 25

a type of cleavage where there is complete division of the egg; occurs in eggs that have little or moderate amount of yolk (isolechithal or mesolecithal) ## Footnote holo = whole (complete) - possible because yolk wouldn't push mitotic spindle to one side of egg.

Question 26

Isolecithal eggs and example of animal w/

Answer 26

eggs that have very little yolk (in mammals)

Question 27

Meroblastic

Answer 27

incomplete cleavage of a yolk-rich egg (telolecithal; birds, fish, insects)

Question 28

Mesolecithal eggs and example of animal w/ this

Answer 28

eggs that have moderate yolk (amphibians)

Question 29

what happens in Morphogenesis

Answer 29

cells become specialized

Question 30

what happens in gastrulation

Answer 30

sets of cells at or near the surface of the blastula move interiorly, germ layers are established and digestive tube is formed.

Question 31

gastrulation in chickens begins from..

Answer 31

a layer of cells called the blastoderm (derm= layer not ball)

Question 32

what is the upper surface of the blastoderm (in chicken gastrulation) called? what does it form? what about the lower surface?

Answer 32

Upper: the epiblast, it forms the embryo. Lower: the hypoblast, it directs the formation of the primitive steak

Question 33

what's the primitive streak (in chicken gastrulation), how is it formed? What cell layers does it form?

Answer 33

a thickening at the midline of the blastoderm, formed when the epiblast cells move toward the midline pile up, before moving into the embryo. From this the mesoderm and endoderm are formed.

Question 34

Where does fertilization take place in humans

Answer 34

in the oviducts

Question 35

Human gastrulation starts with a _ (the mammalian blastula what's it called, and describe it)

Answer 35

The blastocyst, at the end of cleavage the embryo is more than 100 cells arranged in a central cavity, with an inner cell mass at one end (becomes the embryo).

Question 36

Describe the steps of fertilization in humans (in detail)

Answer 36

1. The trophoblast: (outer epithelium of the blastocyst), initiates implantation by secreting enzymes to break down the endometrium. Inner cell mass now consists of the epiblast and hypoblast. 2. The trophoblast expands into endometrium and 4 membranes appear: the allantois, chorion, amnion, and yolk sac (extraembryonic membranes). 3. Gastrulation begins after implantation and proceeds like the chick (cells form primitive streak). But then Trophoblast cells, epiblast cells and endometrial tissue will form the placenta.

Question 37

Unlike other vertebrates (fish, amphibians0 reptile and mammal embryos contain 4 extraembryonic membranes. what are they and what do they do?

Answer 37

1. The allantois: storage of fetal excretions (including gas) 2. Chorion: gas exchange, separates the embryo from albumin (part of placenta). 3. Amnion: provides protection 4. Yolk sac: provides nutrients for the developing embryo.

Question 38

what's different about the extraembryonic membranes for mammals

Answer 38

the allantois is part of the umbilical cord, the chorion forms part of the placenta, the amnion breaks during childbirth, and the yolk sac is for early formation of blood cells.

Question 39

what's neurulation

Answer 39

cells from the dorsal mesoderm form the notochord

Question 40

notochord

Answer 40

rod that extends along the dorsal side of the chordate embryo

Question 41

what forms the neural plate

Answer 41

the ectoderm above the notochord, based on signaling molecules secreted by the mesodermal cells.

Question 42

How is the neural tube formed, what does it become?

Answer 42

the cells of the neural plate curve inward and roll into the neural tube. It becomes the brain and spine.

Question 43

Neural crest what is it what does it form

Answer 43

a set of cells that develops along the borders where the neural tube pinches off from the ectoderm. These cells will migrate long distances to form peripheral nerves, teeth, and skull bones.

Question 44

Somites

Answer 44

groups of mesodermal cells lateral (on each side of) the notochord that separate into blocks. Role in body segmentation, some form mesenchyme cells (gives rise to connective tissues), vertebrae, muscles, along the vertical column, ribs (basically repeating units).