Gametogenesis & fertilization Flashcards
Failure to form viable gametes is a major cause of ___
infertility
What is gametogenesis?
process that produces egg cells in female & sperm cells in male
Defects in gametogenesis may lead to chromosome copy # abnormalities in the zygote which are a primary cause of ___ & ___
preimplantation & early embryonic death
What are the 2 periods of human development. How long do they last?
Embryonic period- fertilization to 8 weeks
- first 4 weeks are used to develop basic body plan of embryo & second 4 weeks for organ formation
Fetal period - subsequent 8 weeks
- growth. This produces final shape & size of new born & final shape & structure of organs
Meiosis produces cells with half of normal number of chromosomes, which is __ # of chromosomes
23
Germ cells contain __ copy(ies) of each chromosome.
1
When does oogenesis begin?
process of oogenesis begins before birth.
At birth, female contains about ___ (#) oocytes, but this number decreases to about ___ by puberty due to ____
2M; 50K; cell death
Oogenesis occurs ___ (Where). Every month about ___ primary oocytes undergo ___, each within a structure called the ___
in the ovary; 15-20; maturation;follicle
Oocytes are arrested in ___ meiosis prior to birth & only complete __ meiosis as they progress towards ____ (after ___)
1st; 1st; ovulation; puberty
they put aside 1 copy of DNA - inert
It is only during ___ that the 2nd meiotic division commences to generate the haploid cell. Second meiosis is completed ONLY when ovum has been ___.
ovulation; fertilized.
The complete process of oogenesis generates a single ovum plus __ (#) nonviable polar bodies, all with 22 + X chromosome complement.
3
In general, only 1 ovum is released during each cycle of ovulation
What are mature sperm cells called?
spermatozoa
The complete process of spermatogenesis generates ___ sperms cells, __ 22 + X & __ 22 + Y
4; 2; 2
Where does sperm development occur?
seminiferous tubules
Maturation of sperm occurs in organized fashion - precursor cells on outside, more ___ cells closer to lumen
differentiated
Infertility in men may be due to ___.
absence of mature sperm near the lumen of seminiferous tubules
Abnormal meiotic divisions can produce either __ or ___ chromosomes in an ovum/sperm
extra or missing
This will later result in variations in chromosome # in fertilized egg
The most commonly observed chromosomal abnormalities are ___
trisomies - 3 copies of a chromosome
____ of chromosome other than sex chromosomes is invariably lethal
loss
What is trisomy 21?
Down’s syndrome & occurs 1/1000 births - very common
Approximately 75% of concepti with trisomy 21 die in embryonic/fetal life. Of those born, approximately 85% survive to age 1 year & 50% can be expected to live to age ___ years/more.
50
What is FISH detection of trisomies?
cells may be collected from amniotic fluid surrounding fetus They can be assayed for correct chromosome #. especially 21, 18 & 13
What is trisomy 13?
Pateau’s syndrome - involves multiple abnormalities, many of which aren’t compatible with life. 50% of infants die after 1st week. More than 80% of children with trisomy 13 die in 1st month. Some live to their teens
observed in about 1/5000
What is Turner’s syndrome?
females inherit single X chromosome - XO
1/3000
variation in sex chromosomes is fairly common
fairly extensive medical issues - short stature, webbed neck reduction in secondary female characteristics, ovaries don’t develop –> sterility
What is Klinefelter syndrome?
extra copy of X in males - XXY
1/700
1 copy of X is inactivated
No major medical problems though they may possess some feminine characteristics - higher voice, breast enlargement reduced body hair
thought to be significantly under diagnosed
What is Robertsonian translocation?
chromosomal rearrangement
translocation between ch13 & ch14 is by far most common
What is spermatogenesis?
Beginning at puberty, germ cells in male undergo standard meiotic division to produce 4 spermatids which later become mature sperm cells - spermatozoa
What is fertilization?
involves successful fusion of male & female gamete cells
Normally occurs in ampullary region of uterine tube (ampulla means flask/bottle); quite close to ovaries
What is capacitation?
removal of GP surrounding sperm when in female reproductive tract
Within female reproductive tract, prior to encountering the ovum, GP surrounding the sperm are removed. Removal of GP is necessary for fertilization to occur
Sperm must penetrate through what layers to enter the ovum?
outer - corona radiata/cumulus oophorus
inner GP layer - zona pellucida
The ability to penetrate the layers of the ovum by the sperm is controlled by ____ enzymes released from tip of sperm
acrosomal
What is the next step after sperm reaches the egg membrane?
Fusion of sperm membrane with oocyte membrane. Fusion event enables sperm head & tail to enter ovum
When is the second meiotic division of ovum completed?
when sperm & egg fuse. Now one set of maternal chromosomes is expelled in 2nd polar body
What is a mechanism to prevent polyspermy?
fast block - change in membrane potential that prevents further sperm fusion events
slow block - at time of sperm entry, ovum undergoes event called cortical reaction. This forms a space between egg membrane & zona pellucida - perivitelline space
Digestive enzymes are releasedd into perivitelline space
At time of sperm entry, ovum undergoes event called ____. This forms a space between egg membrane & zona pellucida = _______
___ enzymes are released into ____ space
cortical reaction; perivitelline; digestive; perivitelline
After entering ovum of tail of sperm degenerates & head enlarges/decondenses to form male ___
pronucleus
Male & female pronuclei fuse to form single diploid nucleus
fertilized egg –> zygote
After fertilization, cell division __. Division occurs about every ___ hours
commenses; 16-24 hrs
The early mitotic division take place without cell growth (reductional division) leading to larger # of ___ cells. Zygotic cells will contribute to __ or ___ tissues
smaller; embryo or extraembryonic tissues
The 8-16 cell stage is called the ___
morula stage.
During early cell divisions (2-cell to 16-cell) all cells are equivalent. Initially they are loosely associated with each other but then they become compacted
Between the 32 & 128 cell stages, the morula begins to organize into a ___/___ around a central cavity called the ___/__ cavity.
blastula/blastocyst
blastocele/blastocyst activity
As cell division continues, embryo moves along uterine tube to uterus (driven by ciliary motion). At about 5-6 at blastocyst stage, the embryo will ___
implant
What causes infertility?
inflammation/tissue damage in uterine tube can prevent access of sperm to egg or movement of zygote into uterus
Defects in ciliary action prevent movement of zygote towards uterus & are major genetic cause of infertility
What is ectopic pregnancy?
when zygote implants in tissue other than uterine wall. This most often occurs in wall of uterine tuber (~95%). The embryo usually dies after about 30 days but this may be associated with severe hemorrhaging which can threaten life of mother
It is estimated that almost ___ of all zyogtes fail to implant
1//2;
Even after successful implantation another 20-25%are lost to spontaneous abortion.
What is a major cause of spontaneously terminated embryos?
congenital abnormalities - ex - heart defects
What is a trophoblast? Most of trophoblast will form the ___ which is a population of cells with 1 nucleus each
cells comprising outer cell layer of blastocyst will form trophoblast
cytotrophoblast
Trophoblast cells close to inner cell mass will form the ___ population. These are multinucleated, highly invasive cells. Retroviral-derived protein, __ is essential for formation of ___ tissue
syncytiotrophoblast; syncytin; syncytiotrophoblast
Attachment of synctiotrophoblast cells to uterine wall begins ___. Initial attachment is mediated by ___ on cell surafce of synctiotrophoblast cells adhering to ___ on endometrium of uterus
implantation; L-selectin; oligosaccharides
After attachment, syncytiotrophoblast cells invade the endometrium of uterus & eventually cover the ___ layer
cytotrophoblast layer
The syncytiotrophoblast cells digest their way into endometrium of uterus & wrap themselves around ___ during invasion
cytotrophoblast
What are fraternal/dizygotic twins?
separate ovulation, fertilizations & implantations
Fraternal twins have genetic component no more alike than any 2 siblings
2/3 of twins
What are monozygotic/identical twins
1/3. Splitting of embryo during early cleavage stages (before 8 cells) or formation of 2 inner cell masses
What are identical triplets?
6% of triplet births
more common are triplets with 1pair of identical twins & 1 independent
Identical twins in same chorion can sometimes ____
fuse to be conjoined
1/200 identical twin births
Twins who are born premature is __
common
__ pregnancy is the largest single cause of multiple births
assisted
multiple births are largest single cause o prematurity
what are serious health consequences of premature birth?
incomplete brain development
respiratory problems
vision, hearing
jaundice (elevated bilirubin levels)
