LEC41: Mitosis and Meiosis Flashcards Preview

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Flashcards in LEC41: Mitosis and Meiosis Deck (37)
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what are the steps of mitosis as visualized in the light microscope?

1) prophase 

2) prometaphase 

3) metaphase

4) anaphase 

5) telophase

6) cytokinesis


what do microtubules and actin filaments do during mitosis? 

do they have distinct or redundant functions in cell division?

microtubules: form as spindles during promteaphase; attach to the chromosome, anchor it to mitotic spindle, interdigitate with each other from opposite poles 

actin: drives cytokinesis, when G1 daughter cells form


in what important way does meiosis differ from mitosis?

Mitosis: process of cell division, from 4N parent to 2 2N daughter cells that are diploid; somatic cells 

Meiosis: germ cells; 2N to 1N haploid cells = reductive division; goes through 2 rounds, Meiosis I and II 


during what phase of meiosis does recombination btwn maternal & paternal chromosomes occur?

Prophase I


what are the 2 major ways by which genetic recombination occurs during meiosis?


1) chromosomal crossing-over (infinite recombination possibilities)

2) independent assortment (limited, 223 recombination possibilities)


what are phases of cell cycle?

S phase: DNA synthesis 

M phase: mitosis, cell division 

G1 & G2: "gap" or "growth" phases, cell syntheizing things that aren't necessary for DNA synthesis (G1) and synthesizing things needed for mitosis (G2)



what is DNA content in each phase of somatic cell cycle?

G1: 2N

S phase: between 2N and 4N

G2: 4N 

M phase: 4N


what does human somatic cell alternate beween?

interphase and mitosis


what is mitosis?

process of cell division

go from one 4N G2 cell to 2 2N G1 daughter cells

G2 > prophase, prometaphase, metaphase, anaphase, telophase > G1 + G1



what happens to centrosomes / microtubule organizing centers during S phase?

they double


prophase steps?


1) centrosomes (2) move to the poles 

2) nuclear membrane breaks down 

3) chromosomes condense, become visible 

4) each pair of sister chromatids are held together by the centromere 



prometaphase steps?


1) spindle fibers (microtubules) form, attach to the kinetochore 

have 3 kinds of microtubules: 

1) astrac MT: position at mitotic spindle 

2) kinetochore MT: attach to chromosomes 

3) polar MT: interdigitate w/ MTs from opposite pole


metaphse steps?


1) chromosomes align in center of mitotic spingle 

2) karyotiping done at this phase



anaphase steps?


1) sister chromatids separate and move to opposite poles 

2) cell elongates in preparation for telophase 


telphase steps?


1) reformation of nuclear membrane 

2) chromosomes decondense (reversal of prophase)

3) spindle, MT, disappear 



when is cytokinesis? 

what drives it?


6th, after telophase 

actin filaments polymerization/depolymerization drives cytokinesis 

result: separation of daughter cells 


what is karyotyping?

number and appearance of chromosomes




process of reductive cell division for germ cells 

each germ cell = 1N, haploid DNA content 


describe chromosome content change over meiosis

start w/ 4N DNA content cell 

Meiosis I: 4N to 2N

Meiosis II: 2N to 1N


DNA content in germ cell vs. somatic cell?

germ cell: 1N DNA content, are haploid 

somatic cell: 2N DNA content, are diploid


what happens in Meiosis I?

pairing and segregation of homologues (paternal or maternal), aka homologous chromosomes separate

go from 4N to 2N DNA content by lining up separate homologues, separting them into poles

result: each daughter gets 1 materal or paternal copy via sister chromatid 


prophase I characteristics?

DNA is condensed

spindle forms at chiasmata, which holds maternal and paternal paris together 

homologous chromosomes align and exchange segments




metaphase I characteristics?

tetrads of sister chormatids align in middle 

microtubules form, attach to kinetochore 



anaphase I characteristics?

pairs of homologous chromosomes split up 

sister chromatids remain attached 


chiasmata function?

holds paternal and maternal chromatid pairs together in meiosis I


when does spindle form in meiosis I?

once chiasmata is in place


what happens in meiosis II?

pairing and segregation of sister chromatids - sister chromatids line up, separate, like in mitosis


what happens to DNA conent during Meiosis II?

start w/ 2N, 23 chromosomes, end up w/ 1N DNA content, each of which has single sister  chromatid


why go through 2 rounds of meiosis?

to cause genetic reassortment


what are 2 ways to accomplishment genetic reassortment?

1) independent assortment: random distribution where 1 maternal chomosome and 1 paternal chromosome / 2nd maternal or paternal chromosome coudl randomly go to a pole; cerates 223 or 8 millino possibilities 

2) crossing over via localized recombination between maternal and paternal chromosomes at the chiasma - can occur limitless number of times in both directions, generates infinite amount of diversity!


what is chiasma's function?

1) physical association: holds together maternal/paternal chromosomes effectively, so at metaphse I of meiosis I they can separate 

2) facilitates chromosomal crossing over, recombination: localized recombination btwn maternal & paternal chromosomes at chiasma, can occur limitless # of times in each direction, creates infinite amount of diversity


why does meiosis occur by DNA syntehsis, followed by Meiosis I and II?

b/c during meiosis I, chromosomal crossing over occurs - homoogous chromosomes exchange genetic materal 

this recombination results in limitless genetic diversity 

explains why meiosis doesn't occur by simple homologues' separation - would not get crossing-over and exchange of genetic material if just had homologues' separation


what is synaptonemal complex?

highly ordered, well-defined cellular structure of 2 lateral elements and a central element 

it is what facilitates recombination btwn paternal and maternal homologues

underlies the chiasma 



what do chiasma do? 

when are they present?

chiasma = remnants of synaptonemal complex

are sites of crossing-over that persist into metaphase of Meiosis I 

physically hold homologues together until segregation occurs, like centromeres for sister chromatids 


how do male sex chromosomes have crossing over?

during Meiosis I 

small region of homology between X and Y chromosomes, allows their pairing 

crossing-over only in this small region 

allows physically keeping the X and Y chromosomes together until segregation is ready to occur


what is non-disjunction?

why does it occur? 

what is result?

when homologues fail to separate in Meiosis I 

occurs if chiasma aren't properly disrupted in Meiosis I

homologous chromosomes stay associated

Meiosis II then occurs normally

resulting germ cells have N+1 (3) or N-1 (1) chromosomes, when should each have 2 chromosomes

3N gametes can continue to fertilization, resulting embryo has extra chromosome, results in a trisomy


when can nondisjunction occur?

most common in Meiosis I, as sister chromatid separation is more tightly controlled process

can occur if sister chromatids fail to separate during Meiosis II 


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