LEC41: Mitosis and Meiosis Flashcards

1
Q

what are the steps of mitosis as visualized in the light microscope?

A

1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase
6) cytokinesis

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2
Q

what do microtubules and actin filaments do during mitosis?

do they have distinct or redundant functions in cell division?

A

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

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3
Q

in what important way does meiosis differ from mitosis?

A

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

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4
Q

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

A

Prophase I

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5
Q

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

A

1) chromosomal crossing-over (infinite recombination possibilities)
2) independent assortment (limited, 223 recombination possibilities)

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6
Q

what are phases of cell cycle?

A

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)

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7
Q

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

A

G1: 2N

S phase: between 2N and 4N

G2: 4N

M phase: 4N

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8
Q

what does human somatic cell alternate beween?

A

interphase and mitosis

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9
Q

what is mitosis?

A

process of cell division

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

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

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10
Q

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

A

they double

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11
Q

prophase steps?

A

first

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

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12
Q

prometaphase steps?

A

2nd

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

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13
Q

metaphse steps?

A

3rd

1) chromosomes align in center of mitotic spingle
2) karyotiping done at this phase

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14
Q

anaphase steps?

A

4th

1) sister chromatids separate and move to opposite poles
2) cell elongates in preparation for telophase

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15
Q

telphase steps?

A

5th

1) reformation of nuclear membrane
2) chromosomes decondense (reversal of prophase)
3) spindle, MT, disappear

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16
Q

when is cytokinesis?

what drives it?

result?

A

6th, after telophase

actin filaments polymerization/depolymerization** **drives cytokinesis

result: separation of daughter cells

17
Q

what is karyotyping?

A

number and appearance of chromosomes

18
Q

meiosis?

produces?

A

process of reductive cell division for germ cells

each germ cell = 1N, haploid DNA content

19
Q

describe chromosome content change over meiosis

A

start w/ 4N DNA content cell

Meiosis I: 4N to 2N

Meiosis II: 2N to 1N

20
Q

DNA content in germ cell vs. somatic cell?

A

germ cell: 1N DNA content, are haploid

somatic cell: 2N DNA content, are diploid

21
Q

what happens in Meiosis I?

A

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

22
Q

prophase I characteristics?

A

DNA is condensed

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

homologous chromosomes align and exchange segments

23
Q

metaphase I characteristics?

A

tetrads of sister chormatids align in middle

microtubules form, attach to kinetochore

24
Q

anaphase I characteristics?

A

pairs of homologous chromosomes split up

sister chromatids remain attached

25
Q

chiasmata function?

A

holds paternal and maternal chromatid pairs together in meiosis I

26
Q

when does spindle form in meiosis I?

A

once chiasmata is in place

27
Q

what happens in meiosis II?

A

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

28
Q

what happens to DNA conent during Meiosis II?

A

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

29
Q

why go through 2 rounds of meiosis?

A

to cause genetic reassortment

30
Q

what are 2 ways to accomplishment genetic reassortment?

A

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!

31
Q

what is chiasma’s function?

A

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

32
Q

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

A

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

33
Q

what is synaptonemal complex?

A

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

34
Q

what do chiasma do?

when are they present?

A

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

35
Q

how do male sex chromosomes have crossing over?

A

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

36
Q

what is non-disjunction?

why does it occur?

what is result?

A

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

37
Q

when can nondisjunction occur?

A

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