Flashcards in Lecture 6 Deck (124):
contains two sets of chromsomes, one from each parent
contains one set of chromosomes
specialized reproductive cells; sperm or eggs gerneated through meiosis
haploid gametes fuse to fomr a diploid cell (Zygote)
divided by mitosis to become a multipcellular organism
gametes and their precursors
form the rest of the body and leave no progeny
chromosomes common to both sexes; one from each parent in each diploid nucleus
X and Y
meiosis creates what two genetic diversity?
Random segregation of homologs during meiosis and crossing over
What arise from meiosis?
involves two cell division buy one round of DNA synthesiss to produce half the number of chromsomes
When do chromosomes replicate?
How are two chromatids bound?
What does homologs do in meiosis I
pair ,recombine, and separate
seperation of homologs in meiosis?
Meiosis II DNA replication?
divided to produce 4 haploid duahgter cells?
sister chromatids in meiosis II
When do homlogs begin to pair?
in prophase I, which can last weeks /day/ years
What is a 4 chromatid structure?
What does a stable piaring require crossing over?
What are hologs joined by protein strucutre?
What small region of homology btw X and Y allows them to piar?
homlogs begin to condesne/pair
homologs pair and synaptonemal complexes form
synapsis is complete; crossing over occurs
synaptonemal complex begins to break down; homologs begin to spearte but remain attached at chiasmata
reach maximum condensation; separation of homologs and transition stage into metaphase
What do transvers filaments btw homlogs form?
synaptonemal complex, important for crossing over
When do cohesin compelxes assemble on DNA?
during S phase and bind sister chromatids
-major components of axial core of each homolog
- play important role in segregating homlogs in meiosis I
What attach to microtubules coming form same pole?
kinetochores on the 2 sister chromatids
When do homlogs separate?
Arms of sitster chromatids separate at anaphase I,
resolving chiasmata and allowing homlogs to seperate
What cleaves the cohesion complexes in sister chromatids in anaphase II?
When is human female meiossi arrestes for years after diplotene?
meiosis I is completed only at ovulation
memiosis II in females is only completed after?
homlogs fail to spearate properly
-erros are very common during egg development and increase with advanceing maternal age
-leading cause of spontaneous abortions and metal retardation in humans
cells with abnormal choromsome numbers
-trsomey 21/down syndrom: most common singl cause of metal retardation
-90% of trisomy 21 individsual, the additional chromsomes is materal in orgin
cells with normal number of chromsomes
random distirbution of maternal/paternal homlogs can produe?
What is variation increased by?
-2-3 crossovers per human homolog
Female mammals begin meiosis in?
the fetal ovary
-arrest in meiosis I
-meosis 1 completed at ovulation
In males meiosis being in the testes at?
-proceeds without arres
-takes 24 days to complete meiosis
20% of eggs are aneuploid vs
only 3 to 4% of sperm
- a cell cycle checkpoint is activated in sperm w metiotic errors, resultiping in apoptosis
25% of all human conceptions are aneuploid
-mostly due to nondisjunction in oocytes at Meiosis I
What are male gametes more prone to?
new DNA mutations as a result of undergoing more mitotic cell divisions
-acvanced paternal age
found in all vertebrate embryos and give rise to gametes
primordial gemr cells(PGCs)
PGCs cells migrate to deleveoping gonads
intially germ cells go through
in mammals, diving egg is totipotnet fo?
fist few rounds of cell division; then differentiate into PGCs
somatic cell fates must be suppressed by?
Translation of certain RNAs must be?
accumulate at pole after fertiliation and?
cell signaling lead to ? in gonaldal development
proliferation and migration of PGCs to developing gonad
uncommitted to cell fate
-can be removed and cultured w signaling protines to fomr cell lines for any cell type for the body except extraembryonic cells---pluripotent
sex chromsomes in genital ridege determine?
Sperm determines sex of
-presence of absence of Y determines sex of indvidual
-45, X patients are still female
genital ridge to develop into testis
-default pathway is female
sex determining region of Y
necessary and sufficient for testis development in mammals
can cause sex reverasl
-XX mouse + SRY= develops as a male(sterile)
-XY male w inactivating SRY mutation=develops as female
differntiate into Sertolie cells
expression of SRY
-testis supprot cells
encodes DNA biding protein that regulates transctiption of genes involved in Sertolie development
What is expressed in all vertebreates?
What does SRY in somatic cells do?
direct differentitation into sertolie cells instead of follicle cells
What doe sertolie cells secrete?
anti mullerian hormone
-suprresses fmale development
-causees mullerian duct to regress
leydig cell differentation in other sperm cells
activated egg can give rise to completely new organisms
What is egg activations triggered by?
fertlization- fusion of sperm and egg
What occurs in some lizards and frogs?
-activation in thea bsence of sperm
-mammals cannot due to imprinting
What can be used to reprogram
stockpiles of nutrients for intial development of the embryo
What is the egg nutritional reserve?
-rich in lipids; protines and polysaccharides
-yolk grandules; discrete yolk-containing structures
What is the egg coat made of?
glycoprotien rich extra cellular matrix
what does the extra cellular matrix protect from?
Oogenesis cells migrate into the gonad?
primordial germ cell
What undergo mitotic cell divisions before entering into meiosis in oogenesisi?
When are primary oocytes fomred?
during gestation of the human embryo
Primary oocytes arrest at?
prophase I of meiosis I
When does primary oocytes resume progression?
How does cytoplams divide in oognesis?
-small polar body
-large secondary oocyte
When is the sendocary oocyte arrested?
How do eggs achieve lg size?
have extra gene copies in the cell
-growth occurs afteer DNA replication
How do eggs import yolk proteins?
through recetor mediated endocytosis
oocyte surrounded by single layer of follicle cells
multiple layers of follicle cells(granulosa cells) surround grwoing oocyte
some developing follicels go on to acquire fluid filled cavity
FSH surge induces 10-12 antral follicels; one becomes dominate
What does the FSH+LH in middle of menstral cycle trigger?
ovulation and primary oocyte...
-no cytoplamic organlels
sperm have two distinct regions
What is the midpiece of a sperm packed wiht?
mitochondria to power flagellum for movment
What proteins are require in sperm?
Dynein motor proteins requre ATP hydorlysis to slide microtubules
What does the acrosomal vescile contain?
-released by exocytosis in acrome reaction
-helps penetrate eggs outer coat
When does meiosis for sperm begin?
When do piared homologs cross over?
prophase I of metaphase
What do primary spermatocytes produce when they complete M I?.
two secondary spermatocytes w 22 duplicated autosomes and X or Y
What happens to sendodary spermatocytes
enters M II to porduce 4 haploid spermatids
What happen to spermatids?
they differentiate into sperm which escape into lumen of seminiferous tubule
Where are sperm stored and undergo further matureation?
primordial germ cell.... spermatogonium.... primary spermatocyte.... secondary spermatocyte... spermatid... mature sperm
Where does spermatogenesis occur?
-maintina close contace with sertoli cells
-spermatogonia undergo limited mitotic dividison before endering meiosis I
Progeny of spermatogonium don't complete?
-they remain connected through cytoplamic bridges---syncytium
-each share common cytoplasm
-produced in synchronous batches
-have access to diploid genome for their development
fusion of egg and sperm
process required to acquire capacity to fertilize an egg
-takes 5-6 hrs in humans
-completed in oviduct
What does sperm undergo during fertilization?
-greatly increases motility of flagellum
-makes sperm capable of undergoing acrosome reaction
What must be present in female genital tract for fertilization to occur?
albumin- helps extract cholestrerol from membran, increasing ability to fuse with acrosome membrane
-Ca2+ and HCO3- activate adenyl cyclase in sperm to produce cAMP---helps to initiate capacitation-associated changes
What is released egg surrounded in?
granulosa cells and ECM rich in hyaluronic acid
What must capacitated sperm penetrate?
granulosa cells using hyaluronidase
WHat does zona pellucida act as?
-induces sperm to undergo acrosome reaction
-help sperm to tunnel
-sperm can bind and fuse w plasma membrane of egg
-sperm binds egg plasma first by tip and then side
What membrane proteins are neded for sperm binding?
ZP1 cross- links filaments
ZP 2 and 3 form long filaments
Fusion with sperm induces?
-cortical granules release contents
-meiosis to resume
What is cortical reation triggered by?
increased Ca2+ in cytosol
-egg activation can be artificailly triggered by injecting CA2+ into egg
Cortical reaction prevents?
Cortical reaction releases enzymes to change?
zona pellucida so sperm cant penetrate
-inactivation of ZP3 so it no longer binds sperm or induces acrosoem reaction
-ZP2 is cleaved which makes ZP impenetrable
What fuse in the zygote?q
2 haploid nuclei (pronuclei)
-forms a single diploid nucleus
What do sperm contribute?
centrosomes and centrioles
-not present in eggs
Sperm contribut cetersome for duplicates to assesmble mitotic spindle, in polyspermy
extra mitotic spindles are present
-leads to fualty segregation of chromosomes and aneuploidy
use foster mother to grow identical clone