Fertilization & Animal Development Flashcards
Define gametogenesis
The production of haploid cells (gametes) for sexual reproduction
Define spermatogenesis
The formation and development of the male gamete (sperm)
Approximately how many weeks does it take to make sperm?
~7 weeks
T or F: production of sperm in adult males is prolific and continuous
True
How many sperm per day does an adult male produce?
hundreds of millions of sperms
Define oogenesis
The development of mature eggs
Where do immature eggs form during oogenesis?
In the fetal ovary
When does the development of immature eggs during oogenesis stop? And when do they begin again?
Stop at prophase I of meiosis
One immature egg will resume meiosis per month after puberty has begun
What is a major difference between the development of mature gametes in spermatogenesis and oogenesis?
In spermatogenesis, all daughter cells develop into mature gametes
In oogenesis, almost all the cytoplasm goes to one daughter cell which will become the egg
When does spermatogenesis occur and for how long? Vs. oogenesis?
Spermatogenesis occurs throughout adolescence and adulthood
Oogenesis completes some stages before birth and stops around age 50
What is a major difference between the production of sperm in spermatogenesis vs that of eggs in oogenesis?
Spermatogenesis produces mature sperm continuously and without pause through a male’s life
But oogenesis has long interruptions, only one egg matures per month.
Describe sperm
Small and motile male gametes that travel from a male to a female to find an egg.
Which structures are found in the ‘head’ of a sperm?
the head of sperm encloses the:
haploid nucleus and the acrosome
Define acrosome
a special vesicle in sperms that contain enzymes that help the sperm penetrate the egg
What is located behind the head of a sperm? And what is the function?
Mitochondria to provide ATP which power the movement of the flagellum tail of sperm (allow the sperm to be motile)
Describe eggs
The large and nonmotile female gametes that remain within a female to carry out their function
Do egg or sperm have a larger cytoplasmic volume?
Egg
How come the zygote usually ends up with much more of, or only, the mother’s mitochondria?
Because the cytoplasm of the zygote is mostly from the egg
Eggs have a much larger cytoplasmic volume than sperms
Define fertilization
The formation of a diploid zygote from the fusion of a haploid egg and sperm
Which animal species has fertilization been highly studied in? Why?
Sea urchins
Because they release their gametes for external fertilization in the water column
Describe acrosomal reaction (sea urchins)
When a vesicle at the top of the sperm head (acrosome) releases hydrolytic enzymes by exocytosis to partially digests the egg’s shell or ECM
Then the acrosomal process (part of the sperm) elongates and penetrates the jelly coat of the egg
When is the acrosomal reaction triggered?
When the head of the sperm contacts part of the egg’s ECM
___ molecules on the tip of the ____ process bind to receptors on the plasma membrane of the ____
PROTEIN molecules on the tip of the ACROSOMAL process bind to the receptors on the plasma membrane of the EGG
T or F: the receptors on the plasma membrane of eggs are species specific
True.
They are species specific and provide a prezygotic barrier
What leads to the fusion of sperm and egg plasma membrane?
Contact between the acrosomal process of the sperm and the egg plasma membrane
What happens when the sperm nucleus enters the egg cytoplasm?
A sodium ion channel opens in the egg’s plasma membrane –> Na+ ions diffuse in causing a change in the electric potential (depolarization)
How quickly does depolarization occur after a sperm binds to an egg?
1-3 seconds after
What is the function of depolarization?
It is the fast block to polyspermy
ie. makes it harder for more sperm to enter the egg
How long does depolarization last?
About a minute
What other reaction does the fusion of egg and sperm trigger?
Cortical reaction (slow block)
Define polyspermy
The fertilization of one egg by more than one male gamete
What is the result of polyspermy
The egg will die
Is the cortical reaction the slow or fast block to polyspermy?
SLOW
What structures create the cortical reaction? How do they trigger the reaction?
Vesicles under the plasma membrane of the egg called CORTICAL GRANULES that fuse with the plasma membrane within seconds of the sperm binding to the egg
How are cortical granules triggered?
By signal transduction
The binding of the sperm head causes the SMOOTH ER to release Ca2+ into the cytosol to trigger the fusion of the cortical granules with the plasma membrane
Once the cortical granules have fused to the plasma membrane what happens?
The contents of the cortical granules are released into the space between the plasma membrane and the Vitelline layer
What is the Vitelline layer?
the structure formed between the extracellular matrix of the egg
What occurs after the contents of the cortical granules have been released between the plasma membrane and the Vitelline layer?
- The Vitelline layer is lifted away from the egg by enzymes that break the bonds between the V layer and the plasma membrane and carbohydrates that draw water into the space by osmosis
- enzymes from the cortical granules harden the V layer into a protective fertilization envelope
What purpose do the enzymes from cortical granules serve after separating the Vitelline layer?
They harden the Vitelline layer into a protective fertilization envelope = creating the slow block
What activates the egg?
A rise in Ca2+ levels causes marked increase in the rate of cellular respiration and protein synthesis which requires only the proteins and mRNAs already present in the egg cytoplasm
How long after the sperm nucleus enters the egg will nuclei fusion occur in sea urchins?
~20 minutes
What occurs right after the fusion of the sperm and egg nuclei?
Mitosis begins and the first cell division marks the end of fertilization
T or F: fertilization in mammals and other terrestrial animals, like sea urchins, is external
FALSE.
It is internal in mammals
What are the functions of secretions in the female mammalian reproductive tract?
1 provide moist environment
2. change sperm motility and structure to enable sperm to fertilize egg
What structure must sperm cells travel through in mammals?
Follicle cells
What is the structure on the ECM of mammal eggs called that have receptors for sperm?
Zona pellucida
When sperm bind to the receptors on the zona pellucida, what occurs?
It induces the acrosomal reaction and passage through the ECM
What is a major difference between the blocks to polyspermy in mammals vs sea urchins?
Sea urchins use both the fast and slow block
Mammals only use the slow block