Topic 6: Reproduction and Development, pt 2 Flashcards
Steps of fertilization, types of embryonic development, steps of development
What are the main 4 steps of embryonic development, define each step
- 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
What are the 3 ways embryos can develop (difference are in where they develop)
- Oviparity: development takes place outside of female (in egg) ex: reptiles that lay eggs
- Oviviparity: embryos develop inside the female, off the egg yolk for nutrition, hatch inside, and then released. ex; most sharks.
- Viviparity: embryonic development takes place inside the female reproductive tract and is birthed live.
Fill in blanks with ploidy of each
Fertilization is the formation of a _ zygote from _ gametes.
diploid zygote, haploid gametes
How is it ensured that sperm of the same species penetrates the egg? This also prevents polyspermy (entry of multiple sperm)
Molecules on the sperm bind to receptors on the egg plasma membrane.
why are sea urchins the model for studying fertilization
Their gametes are easy to collect because there’s a lot of them and fertlization is external.
list the steps of fertilization in order
(the sperm penetrating the egg)
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.
Describe what happens when sperm contacts the egg’s jelly coat
This triggers exocytosis of the sperm’s acrosome
(expels its enzymes on the surface of the egg)
Desribe the acrosomal reaction
Hydrolytic enzymes are released from the acrosome which dissolve a hole into the jelly coat.
what forms the acrosomal process, what happens in this process
(within the acrosomal reaction)
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
What does the fusion of the sperm and egg membranes trigger
Depolarization of the membrane (sodium ions diffuse into the egg cytoplasm, decreasing membrane potential).
is fusion and depolarization of the membrane, a fast or slow block to polyspermy? how does it block? how long does it last
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.
Describe the Cortical reaction. Is it a fast or slow block to polyspermy?
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
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.
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
How long does it take for the first cell division post sperm binding in mammals
12-36 hours
In terrestrial animals eggs are fertlized internally, what surrounds the egg that the sperm must penetrate to get to the egg
The follicular support cells.
what’s the zona pellucida
the extracellular matrix surrounding a mammalian egg.
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
interphase and growth (G) phase
So it just has S (synthesis) and M (mitosis) phase
Cleavage
a series of rapid cell divisions without the G1 and G2 phase of the cell cycle.
Cleavage splits the cytoplasm of the fertilized egg into many smaller cells called _?
blastomeres
Fill in the blanks
The first 5-7 cleavage divisions produce the _, surrounding a fluid-filled _
Blastula (hallow ball of cells), blastocoel (blastulas cavity).
Where is the yolk (stored nutrients) located in frog eggs
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)
fill in the position
first 2 cleavage divisions are _ to the poles of the embryo
parallel (from top to bottom)
what direction fill in
Third cleavage division is _
perpendicular (across pole axis), opposite direction of first two divisions.
Yolk in the vegetal pole pushes the mitotic apparatus into the animal pole, which results in
smaller blastomeres in the animal pole compared to the vegetal pole what is this called
Holoblastic
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)
holo = whole (complete) - possible because yolk wouldn’t push mitotic spindle to one side of egg.
Isolecithal eggs and example of animal w/
eggs that have very little yolk (in mammals)
Meroblastic
incomplete cleavage of a yolk-rich egg (telolecithal; birds, fish, insects)
Mesolecithal eggs and example of animal w/ this
eggs that have moderate yolk (amphibians)
what happens in Morphogenesis
cells become specialized
what happens in gastrulation
sets of cells at or near the surface of the blastula move interiorly, germ layers are established and digestive tube is formed.
gastrulation in chickens begins from..
a layer of cells called the blastoderm (derm= layer not ball)
what is the upper surface of the blastoderm (in chicken gastrulation) called? what does it form? what about the lower surface?
Upper: the epiblast, it forms the embryo. Lower: the hypoblast, it directs the formation of the primitive steak
what’s the primitive streak (in chicken gastrulation), how is it formed? What cell layers does it form?
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.
Where does fertilization take place in humans
in the oviducts
Human gastrulation starts with a _ (the mammalian blastula what’s it called, and describe it)
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).
Describe the steps of fertilization in humans (in detail)
- 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.
Unlike other vertebrates (fish, amphibians0 reptile and mammal embryos contain 4 extraembryonic membranes. what are they and what do they do?
- 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.
what’s different about the extraembryonic membranes for mammals
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.
what’s neurulation
cells from the dorsal mesoderm form the notochord
notochord
rod that extends along the dorsal side of the chordate embryo
what forms the neural plate
the ectoderm above the notochord, based on signaling molecules secreted by the mesodermal cells.
How is the neural tube formed, what does it become?
the cells of the neural plate curve inward and roll into the neural tube. It becomes the brain and spine.
Neural crest what is it what does it form
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.
Somites
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).
