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
What is a major difference between the penetration of sperm into the egg of mammals vs. sea urchins?
Sea urchins: the acrosomal process extends from the sperm and releases the nucleus into the egg
Mammals: the enter sperm enters the egg
What is a major difference between the timeline of nuclei fusion in mammals vs sea urchins?
Much slower in mammals, the nuclei don’t truly fuse until first mitosis = ~12-36 hours after sperm binding
~90 mins in urchins
Define cleavage
A succession of rapid cell divisions without growth that occurs after fertilization
Which cell division stages occur during cleavage?
S phase of interphase and mitosis
What does cleavage produce?
Blastomeres
Define blastomeres
The many small cells produced by cleavage
What are the two groups of stomias?
- Protostome
2. Deuterostome
Define blastula
A hollow ball of cells produced by cleavage with a fluid-filled cavity (blactocoel)
Define blastocoel
A fluid-filled cavity within a blastula
T or F: in sea urchins, blastomeres are a variety of sizes
FALSE. in sea urchins, blastomeres are ALL THE SAME SIZE
T or F: in frogs and other animals, blastomeres are all the same size - why/why not?
FALSE
uneven distribution of yolk leads to differently sized blastomeres
What is yolk?
stored nutrients
What are the two poles of an egg?
Vegetal pole
Animal pole
What is the vegetal pole?
The pole/end of the egg that has a higher concentration of yolk and therefore larger blastomeres
What is the animal pole?
the pole/end of the egg opposite of the vegetal pole that usually has no yolk and smaller blastomeres
What are protostomes?
Animals with mouths as the first opening in their digestive tracts
Cleavage creates blastomeres in what kind of arrangement in protostomes?
Spiral arrangement
What are deuterostomes?
Animals with mouths as the second opening in their digestive tracts
Cleavage creates blastomeres in what kind of arrangement in deuterostomes?
The plane of cleavage is parallel or perpendicular to the polar axis
So cells are arranged directly above or below each other
In frogs, what do the first 2 cleavages form?
4 equally sized blastomeres
In frogs, how does the third cleavage occur (symmetrically or asymmetrically)? And what is the result?
Asymmetrical cleavage results in:
Animal pole having smaller blastomeres (no yolk)
Vegetal pole having larger blastomeres (yolk)
When does cleavage end in animals?
When the ratio of material in the nucleus to cytoplasm is sufficiently large so that mRNA synthesis can occur
What happens to the rate of cell division after cleavage ends?
It slows and the normal cell cycle is restored
Define gastrulation
Occurs when a set of cells near the surface of a blastula moves to an interior location and forms a GASTRULA
What is the function of gastrulation?
It rearranges the shape of the blastula into a three-layered embryo (usually) called a gastrula
What is a gastrula?
The (usually) 3-layered embryo formed by gastrulation
Animals with all three germ layers are called?
Triploblasts
Animals with only two germ layers are called?
Diploblasts
What kind of symmetry do animals with three germ layers have?
Bilateral
What kind of symmetry do animals with 2 germ layers have?
Radial
What is the blastopore?
the first hole that forms during gastrulation
Where do cells first move into during gastrulation?
Cells move in at the blastopore at the open end of the archenteron
Define archenteron
The cavity formed during gastrulation that develops into the digestive tract of the animal
What will the blastopore become in protostomes?
the mouth
What will the blastopore become in deuterostomes?
the anus
Define germ layers
The embryonic tissue layers produced by gastrulation that will develop into specific structures in the adult animal
What are the 3 germ layers?
- ectoderm (outer)
- mesoderm (middle)
- endoderm (inner)
What 8 structures will the ectoderm develop into?
- epidermis of the skin and its derivatives (ex. sweat glands, hair follicles)
- nervous system
- sensory system
- pituitary gland
- adrenal medulla
- jaws
- teeth
- germ cells
What 8 structures will the mesoderm (if present) develop into?
1 skeletal system
2 muscular system
3 circulatory system
4 lymphatic system
- excretory system
6 reproductive system (except germ cells)
7 dermis of skin
8 adrenal cortex
What 5 structures will the endoderm develop into?
- epithelial lining of digestive tract and associated organs (liver, pancreas)
- epithelial lining of respiratory, excretory, and reproductive tracts and ducts
- thymus gland
- thyroid gland
- parathyroid gland
T or F: all vertebrate embryos require an aqueous environment for development?
True
What adaptation did reptiles and mammals develop to allow their offspring to survive on land?
embryo development on land in its own small aqueous environment (ex. amniotic eggs)
T or F: mammal and reptile embryos are surrounded by a fluid in a sac that protects the embryo from desiccation
TRUE
Define monotremes
Egg laying mammals
What adaptation did reptiles and monotremes develop to slow dehydration of embryos on land?
Shelled eggs
What adaptation did marsupials develop to slow dehydration of embryos on land?
Embryos develop in mother’s body but complete development in a pouch
What adaptation did eutherians develop to slow dehydration of embryos on land?
Embryos develop in utero and are nourished by a placenta
Define amniotic egg
Egg that contains 4 specialized extraembryonic membranes
Which type of animals lay amniotic eggs?
reptiles (including birds)
mammals
What are the 4 extraembryonic membranes of amniotic eggs?
- amnion
- allantois
- chorion
- yolk sac
Describe the amnion membrane
fluid filled cavity that bathes, protects, and cushions the embryo against mechanical shock
Describe the allantois membrane
disposal sac for some liquid metabolic wastes and a respiratory organ
Describe the chorion membrane
Allows gas exchange to occur
Describe the yolk sac membrane
Contains stored nutrients (yolk) which are transported to the embryo by blood
Do mammals have the four extraembryonic membranes? why/why not?
No because the placenta and umbilical cord can carry out all the functions
What 3 purposes do the placenta and umbilical cords serve in mammals?
Transport nutrients to the embryo
exchange gases
dispose of nitrogenous wastes
What are the 2 stages of embryo development in mammals and approx when do they occur in humans?
- embryo: first 7 weeks in humans
2. fetus: 8 weeks until birth
Define fetus
A developing mammal in utero with all the major structures of an adult
forms about 8 weeks after conception
Define neurulation
the first steps in forming the brain and spinal cord in vertebrates
Define notochord
the rod that extends along the dorsal side of the embryo
What will replace the notochord?
the vertebrae
Describe spina bifida and how it occurs/what the results are
If portions of the neural tube fail to develop or close properly in humans
Causes nerve damage due to the opening in the spinal column and can cause paralysis but surgery can repair the opening
How does anencephaly occur? What are the consequences?
if an error occurs in the anterior neural tube, the embryo will not develop a cerebrum
It is fatal
Define morphogenesis
The physical processes that given an organism its shape
It involves the movement of cells in animals by changing the shape of the cytoskeleton
Does morphogenesis occur in plants? why/why not?
No because they have cell walls that prevent this from happening
What can occur after gastrulation?
Either continuous or discontinuous development, depending on the animal type
Define continuous development and give an example of an animal that does this
Animals develop directly from gastrulae into adults
ex. humans
Define discontinuous development and give an example of an animal that does this
Different stages of development have different body forms
Most animals have at least one larval stage
ex. frogs
Define larva
A free-living, sexually immature form of an animal that is usually different in form, nutrition, and habitat than the adult
What are 2 functions of larvae?
Help with dispersal of the population
Enable animals to exploit niches different from the adults and therefore reduce interspecies competition
Define metamorphosis
A developmental transformation that turns the animal into a juvenile which represents the adult but is sexually immature
ex. larvae – metamorphosis –> adult
What are the 3 process used to change a zygote into the organism it will become?
cell division
cell differentiation
morphogenesis
How come genes are expressed differentially?
Because almost all cells have the same genome
What are the 2 major sources of direction for the cells/developmental mechanisms?
cytoplasmic determinants
induction
