Exam #2 - Worksheet 1 and 2 Flashcards
Cloning, Evolution, and Blastulation and Nontraditional fertility Methods
What are the six steps that take place during fertilization?
- Initial contact between egg and sperm
- Entry of sperm into egg
- Prevention of polyspermy
- Metabolic activation of the egg
- Completion of meiosis by the egg
- Formation of pronuclei and pronuclei fusion
What are the male considerations in the first step in fertilization?
- initial contact between egg and sperm
-Need 60-100 million sperm/mL
Sperm Capacitation: Incubation within the female reproductive tract (5-6 hours in primates, 1 hour in mouse)
-Necessary for acrosome reaction and coagulation/liquification reaction
-Sperm swims for 72 hr, capable of fertilizing for 48hr (Positive rheotaxic response= swims against flow)
-Sperm agglutination: sperm stick together making it difficult for them to swim
What are the female considerations in the first step in fertilization?
-Vaginal contractions help propel sperm (there are prostaglandins in semen that can cause this)
-Low viscosity cervicle mucous midcycle
-If no chemoattractant from egg 50/50 chance of reaching the right tube
-Egg delivered into fallopian tube by cilliary beating
-Fertilizationg takes place in upper 1/3 of tube and egg is only “ripe” for 24 hr
What happens in the second stage of fertilization?
- Entry of sperm into egg
Sperm penetrate between cells of Corona Radiata
-noncapacitated sperm or sperm where acrosome reaction occured prematurely can not pass
Acrosome Reaction: Allows sperm to dissolve through Corona Radiata and Zona Pellucida (involves hyaluronidase and acrosin enzymes)
Sperm bind to the Zona Pellucida
ZP3 is one of three glycoproteins that make up the membrane surrounding the oocyte and it ensures that sperm of a dissimilar species do not penetrate the zona pellucida
Fusion of Sperm and Egg Plasma Membrane
TCTE-1 receptor: species specific binding of sperm with egg
What happens in the third stage of fertilization?
- Blocks to polyspermy
Fast Block
-2-3 sec, lasts for 60 seconds
-Influx of Na+
-Depolarization from -70mv to +10mv
-Helps repell sperm from attaching to Zona
Slow Block
-Ca2+ release by egg
-Causes rupture of cortical granuoles
-Causes conformational change of ZP3 receptors so sperm detach
-Plasma membrane hardens
Embryos that have dispermy usually abort
What happen in the fourth stage of fertilization?
- Metabolic activation of egg
-ZP3 receptor binding
-Na+ influx
-H+ efflux (increase in pH- becoming more basic)
-Acrosome rxn triggers membrane G proteins
~Second messenger systems:
-Protein Kinase C
-Inositol Tri Phosphate
^These cause Ca2+ release from E.R. and an increase in protein synthesis
What happen in the fifth stage of fertilization?
- 2nd Meiotic division complete
In this stage Meiosis II is finally completed in the egg.
What happen in the sixth stage of fertilization?
- “Fusion” of Pronuclei
-12 Hr in mammals
-Decondensation of egg and sperm chromatin
-Replication of DNA (anticipation of mitosis)
-Dissolution of both pronuclear membrane
-Formation of spindle fibers
-Mitosis “cleavage” resulting in 2 cells
First diploid nucleus is not seen in zygote stage… it’s seen in the two cell stage
What is Procardia and what does it do?
Procardia is a drug used as a male contraception
its a heart calcium blocker
-men on the drug have fertility problems
-prevents sperm acrosome reaction
-blocks penetration of zona pellucida
What are the fertility statistics for 1 year? 1 month? 3 months? 9 months?
90% conceive in 1 year
20% in 1 month
50% in 3 months
75% in 9 months
What 3 methods induce superovulation?
- GnRH Agonists (enhancers), “Lupron”
- Clomiphene Citrate “Clomid”
- HMG
What is GnRH Agonists, “Lupron” and what is used for? How does it work?
its an enhancer and it is used to induce superovulation
-Powerful, directly stimulate LH, FSH output
-Can overstimulate ovary to produce too many eggs per cycle (10-20)
-Ovarian Hyperstimulation Syndrome (OHSS): excessive fluid into abdomen tends to thicken blood, risk of stroke
What is Clomphene Citrate “Clomid” and what is used for? How does it work?
Used to induce superovulation
-Milder stimulation, oral medication that competes with estrogen at Ant. Pit. suppressing its negative feedback
-Increases output of LH, FSH
-Multiple ovulation (6-8 eggs/cycle)
What is GnRH Agonists, “Lupron” and what is used for? How does it work?
used to induce superovulation
-LH, FSH from menopausal urine
-Not really used anymore
-hCG given on last day triggers ovulation
What are the 4 techniques used for mammalian cloning?
- Cleavage separation (Embryo Twinning)
- Nuclear transfer (Wilmut Method “Dolly the Sheep”)
- “Therapeutic” Cloning
- Parthenogenesis
What is Cleavage Separation? How does it work?
a mammalian cloning technique
also known as embryo twinning
- strip zona off at 2 cell stage
- separate blastomeres
- add artificial zona
- culture new embryos
What is Nuclear Transfer Technique? How does it work?
a mammalian cloning technique
also known as the Wilmut Method “Dolly the Sheep”
- culture mammary tissue on minimal media
- starve cells into quiescent state
- irradiate nucleus into egg
- stimulates w electricity
- culture or implant in uterus of surrogate mother
What is “Therapeutic” cloning? How does it work?
a mammalian cloning technique
- same as nuclear transfer technique
- Rather than growing infant, embryo is separated into blastomeres
- Blastomeres used to grow embryonic stem cell lines
- Could be used for growing organs for transplant
What does Parthenogenesis mean? what is it and how does it work?
It means an egg is hatched without ever being fertilized, think of the komodo dragons.
a mammalian cloning technique
- can use chemicals, electricity, or other stimulants to make egg act as though it is fertilized
20% of infertility problems are due to issues with:
- Varicocele
- cervical mucous
- infection
- male or female antisperm antibodies
What are the 3 egg classifications by their yolk amounts? Examples?
Microlecithal: Small amount of yolk
-amphioxus and mammals
Mesolecithal: Moderate amount of yolk
-amphibians, cyclostomes(lamprey), lung fish
Macrolecithal: Large amount of yolk
most fish, reptiles, aves, and monotremes
What are the 3 egg classifications by their yolk distribution? Examples?
Oligolecithal (isolecithal): even yolk distribution
-Most microlecithal eggs
Telolecithal: Uneven yolk distribution
-Most mesolecithal and macrolecithal eggs
Centrolecithal: Central yolk distribution
-Insects and Arthropods
How many days prior to ovulation is yolk produced?
7 - 8 days prior
What triggers yolk production?
estrogen from follicular cells
