Flashcards in Lecture 2 Deck (54):
2 ways to get genetic variagtion
mutaion and sexual reproduction... mutation only way to get new information
crossing over and independnt assortment and fertilization
the production of haploid gametes
the fuiosn of haploid gametes
consequences of meiossi
DNA synthesis and chromosomes replication phase
seperation of homologous chromosome pairs, and reduction of the chromosome number by half
seperation of sister chromatids, also known as equational division
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
spermatogensis. oogenesis... produces sperm and eggs
pairing of homologous chromosmes
two consectutive cell divisions but only one cycle of DNA replication
1. once chromosome possesses the A and B allele
2. and the homologous chromosomes possesses the a and b allele
3. DNA replication in the S phase produces identical sister chromatids
4. During crossing over in prophase I, segments of nonsister chromatids are exchanged.
MEIOSIS I AND II
5. 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.
meiosis I.... Diploid to haploid
Meiosis II... haploid
pachytene... synaptonemal complex
diplotene.. bivalent or tetrad, chiasmata
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...
start ot pair up, homologous chromsomses pair(synapsis).. synaptonemal complex forms, results in bivalents(tetrads)
thick... starting to condense.. shorter and thicker... crossing over begins
later like structure btw to chromosomes... alignment mechanims... if this does not work correctly duplicaiton and deletion occurs... equal crossing overs.
start to see tetrads(bivalents)
seee cross over points, chiasmata(pt where crossover occurs) are well defined
cross over points start to move toward the end... homoloug pair and crossing over. termilalization occurs. spidle apparatus in place. nuclear memnbrane disrupted
Centromeres DONOT divide, random alignment of homologus pairs of chromosomes along the metaphase plate
synopsis... pair up.
move to opposite poles... not idintical bc of crossing over... haploid.... second mechanism of generating genetics variation in the newly formed gamates
cytokinesis occurs, neclear membrane reforms. spinndle apparatus disassembles... HAPLOID.... INterkinesis...
nucler membranes reform, spindle apparatus disassembles, chromsomes may uncoil to vaying degress... spindle usually breaks down.... no DNA synthesis takes place
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)
chromosmes line up on equtorial plate... kinetochoroes face opposite poles...
centromeres have split... sister chromatids seperate... chromosmes move to opposite poles... each consists of single chromatid
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.
the cytoplasm divides to produce tow cells, each having half the orginal number of chromosomes
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
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
keeps sists kinetochores oriented toward same pole during metaphase i
in lecture 2
spermatogenesis... primordial germ cells
diploid... divide mitotically to produce dipoloid spermatogonia
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
crossing over and independent assortment and fertilization
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
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