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2 ways to get genetic variagtion

mutaion and sexual reproduction... mutation only way to get new information

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meiosis

crossing over and independnt assortment and fertilization

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the production of haploid gametes

meiosis

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the fuiosn of haploid gametes

fertilization

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consequences of meiossi

genetic variation

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interphase

DNA synthesis and chromosomes replication phase

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seperation of homologous chromosome pairs, and reduction of the chromosome number by half

meiosis 1

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seperation of sister chromatids, also known as equational division

meiosis II

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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

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gametognesis

spermatogensis. oogenesis... produces sperm and eggs

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synapsis

pairing of homologous chromosmes

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crossing over

in meiosis

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meiosis requires

two consectutive cell divisions but only one cycle of DNA replication

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crossing over

1. once chromosome possesses the A and B allele
2. and the homologous chromosomes possesses the a and b allele
DNA SYNTHESIS
3. DNA replication in the S phase produces identical sister chromatids
CROSSING OVER
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

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produces variation without crossing over

independent assortment... needs more than on pair of chromsomes... line up as homologous pairs in varies ways.

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reduction divison

meiosis I.... Diploid to haploid

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equational division

Meiosis II... haploid

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prophase I

Leptotne
zygotene
pachytene... synaptonemal complex
diplotene.. bivalent or tetrad, chiasmata
diakinesis

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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...

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zygotene

start ot pair up, homologous chromsomses pair(synapsis).. synaptonemal complex forms, results in bivalents(tetrads)

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pachytene

thick... starting to condense.. shorter and thicker... crossing over begins

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synaptonemal complex

later like structure btw to chromosomes... alignment mechanims... if this does not work correctly duplicaiton and deletion occurs... equal crossing overs.

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diplotene

start to see tetrads(bivalents)
seee cross over points, chiasmata(pt where crossover occurs) are well defined

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diakinesis

cross over points start to move toward the end... homoloug pair and crossing over. termilalization occurs. spidle apparatus in place. nuclear memnbrane disrupted

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metaphase I

Centromeres DONOT divide, random alignment of homologus pairs of chromosomes along the metaphase plate

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prophase I

synopsis... pair up.

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anaphase I

move to opposite poles... not idintical bc of crossing over... haploid.... second mechanism of generating genetics variation in the newly formed gamates

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Telephase I

cytokinesis occurs, neclear membrane reforms. spinndle apparatus disassembles... HAPLOID.... INterkinesis...

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interkinesis

nucler membranes reform, spindle apparatus disassembles, chromsomes may uncoil to vaying degress... spindle usually breaks down.... no DNA synthesis takes place

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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)

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metaphase II

chromosmes line up on equtorial plate... kinetochoroes face opposite poles...

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anaphase II

centromeres have split... sister chromatids seperate... chromosmes move to opposite poles... each consists of single chromatid

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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.

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cytokinesis meiosis

the cytoplasm divides to produce tow cells, each having half the orginal number of chromosomes

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cohesion.

holds chromatids together during early parts of mitosis... break down allows sister chromatids to spearate during mitosis anaphase

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cohesion during meiosis

chromosomes arms holds homologous chromsomes together at chiasmata through metaphase I

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meiosis specific cohesions at centromere ...

keeps sister chromatids together during anaphase...

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the cohesion that protects anaphase of sister chromatids during meiosis is

shugoshin

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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

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Keeps separase inactive during interphase and early mitosis

securin

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keeps sists kinetochores oriented toward same pole during metaphase i

monopolins

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48 mins

in lecture 2

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spermatogonia--->

...

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spermatogenesis... primordial germ cells

diploid... divide mitotically to produce dipoloid spermatogonia

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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

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Sour of genetica variation

mutation and sexual reproduction

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meiosis includes

crossing over and independent assortment and fertilization

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Spermatogonia-->

primary spermatocytes 2N

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primary spermatocytes 2N 1-->

secondary spermatocytes N 2... haploid, undergo meiosis II to produce haploid spermatids

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secondary spermatocytes 2.... N-->

4 spermatids N... haploid, differentiate into haploid sperm

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oogonia-->

2n primary oocytes.... arrests at diploteme of prophase I

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Primary ooctye 2N-->

seondary oocyte.... willl also divide off polar body... will go to 2nd metaphase that is ovulated and stop unless fertilized...

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secondary oocyte fertilized

ootid and polar body

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primary oocyte

lg ovum and small polar body, meiosis will not re