Lecture 2 Flashcards
meiosis
crossing over and independnt assortment and fertilization
2 ways to get genetic variagtion
mutaion and sexual reproduction… mutation only way to get new information
the production of haploid gametes
meiosis
the fuiosn of haploid gametes
fertilization
consequences of meiossi
genetic variation
interphase
DNA synthesis and chromosomes replication phase
seperation of homologous chromosome pairs, and reduction of the chromosome number by half
meiosis 1
seperation of sister chromatids, also known as equational division
meiosis II
major results of meiosis
increase in cell numbers sometimes, duaghter cells are not genetically identical, daugther cells are haploid, formation of gametes… compare to mitosis
gametognesis
spermatogensis. oogenesis… produces sperm and eggs
synapsis
pairing of homologous chromosmes
crossing over
in meiosis
meiosis requires
two consectutive cell divisions but only one cycle of DNA replication
crossing over
- once chromosome possesses the A and B allele
- and the homologous chromosomes possesses the a and b allele
DNA SYNTHESIS - DNA replication in the S phase produces identical sister chromatids
CROSSING OVER - During crossing over in prophase I, segments of nonsister chromatids are exchanged.
MEIOSIS I AND II - after meiosis I and II, each of the resulting cells carries a unique combination of alleles
produces variation without crossing over
independent assortment… needs more than on pair of chromsomes… line up as homologous pairs in varies ways.
reduction divison
meiosis I…. Diploid to haploid
equational division
Meiosis II… haploid
prophase I
Leptotne zygotene pachytene... synaptonemal complex diplotene.. bivalent or tetrad, chiasmata diakinesis
leptotene
exteneded state, microscopically can’t be discerned as indviduals… thread like, very thin, each chormosome still two chromatids(replication has already occured)… start to condense…
zygotene
start ot pair up, homologous chromsomses pair(synapsis).. synaptonemal complex forms, results in bivalents(tetrads)
pachytene
thick… starting to condense.. shorter and thicker… crossing over begins
synaptonemal complex
later like structure btw to chromosomes… alignment mechanims… if this does not work correctly duplicaiton and deletion occurs… equal crossing overs.
diplotene
start to see tetrads(bivalents)
seee cross over points, chiasmata(pt where crossover occurs) are well defined
diakinesis
cross over points start to move toward the end… homoloug pair and crossing over. termilalization occurs. spidle apparatus in place. nuclear memnbrane disrupted
metaphase I
Centromeres DONOT divide, random alignment of homologus pairs of chromosomes along the metaphase plate
prophase I
synopsis… pair up.
anaphase I
move to opposite poles… not idintical bc of crossing over… haploid…. second mechanism of generating genetics variation in the newly formed gamates
Telephase I
cytokinesis occurs, neclear membrane reforms. spinndle apparatus disassembles… HAPLOID…. INterkinesis…
interkinesis
nucler membranes reform, spindle apparatus disassembles, chromsomes may uncoil to vaying degress… spindle usually breaks down…. no DNA synthesis takes place
prophase II
chromsomes condense… each chromosmes has 2 chromatids… nuclear membrane disapears, each chromosmes has two chromatids …e ach daughter cell has one complete set of chromosomes (haploid)
metaphase II
chromosmes line up on equtorial plate… kinetochoroes face opposite poles…
anaphase II
centromeres have split… sister chromatids seperate… chromosmes move to opposite poles… each consists of single chromatid
telophase II
chromosmes uncoil, Four geneticall unique haploid cells!!! 4. is one compelte set… cytokinesis is complete. nuclear membre reforms.spindle aparatus disintigrates … chromosomes arrive at the spindle poles.
cytokinesis meiosis
the cytoplasm divides to produce tow cells, each having half the orginal number of chromosomes
cohesion.
holds chromatids together during early parts of mitosis… break down allows sister chromatids to spearate during mitosis anaphase
cohesion during meiosis
chromosomes arms holds homologous chromsomes together at chiasmata through metaphase I
meiosis specific cohesions at centromere …
keeps sister chromatids together during anaphase…
the cohesion that protects anaphase of sister chromatids during meiosis is
shugoshin
separase
kept inactive during interphase and early mitosis, breaks down cohesion at end of metaphase, breakse down meiosis-specific cohesion at centromere during end of metaphase II
Keeps separase inactive during interphase and early mitosis
securin
keeps sists kinetochores oriented toward same pole during metaphase i
monopolins
48 mins
in lecture 2
spermatogonia—>
…
spermatogenesis… primordial germ cells
diploid… divide mitotically to produce dipoloid spermatogonia
spermatogonia are
diploid
can undergo repereated rounds of mitosis to produce more spermatogonia
may initiate meiosis and enter into prophase I to give rise to primary spermatocyte
Sour of genetica variation
mutation and sexual reproduction
meiosis includes
crossing over and independent assortment and fertilization
Spermatogonia–>
primary spermatocytes 2N
primary spermatocytes 2N 1–>
secondary spermatocytes N 2… haploid, undergo meiosis II to produce haploid spermatids
secondary spermatocytes 2…. N–>
4 spermatids N… haploid, differentiate into haploid sperm
oogonia–>
2n primary oocytes…. arrests at diploteme of prophase I
Primary ooctye 2N–>
seondary oocyte…. willl also divide off polar body… will go to 2nd metaphase that is ovulated and stop unless fertilized…
secondary oocyte fertilized
ootid and polar body
primary oocyte
lg ovum and small polar body, meiosis will not re
