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Genetics > Chapter 4.4: Meiosis: Cell Divisions That Halve Chromosome Number > Flashcards

Chapter 4.4: Meiosis: Cell Divisions That Halve Chromosome Number Flashcards

1
Q

What phase of meiosis does the nuclear membrane breaks down and the spindle begins to form?

A

diakinesis of prophase I of meiosis I

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2
Q

What phase of meiosis does  Sister chromatids attach to fibers from the same pole?

A

metaphase I

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3
Q

What are somatic cells?

A

• The mitotically dividing and G0-arrested cells are the so-called somatic cells whose descendants continue to make up the vast majority of each organism’s tissues

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4
Q

Describe prophase II (3)

A

 Chromosomes condense
 Centrioles move toward the poles
 The nuclear envelope breaks down

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5
Q

What phase:  Cytokinesis?

A

telophase II

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6
Q

What phase of meiosis does • Chromatids thicken and shorten?

A

diakinesis of prophase I of meiosis I

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7
Q

Describe the difference between mitosis and meiosis in term of number of divisions

A

Mitosis: One round of division

Meiosis: Two rounds of division, meiosis I and meiosis II

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8
Q

Describe the difference between mitosis and meiosis in term of products

A

Mitosis: Mitosis produces two new daughter cells, identical to each other and the original cell. Mitosis is thus genetically conservative

Meiosis: Meiosis produces four haploid cells, one (eggs) or all (sperm) which can become gametes. None of these is identical to each other or to the original cell, because meiosis results in combinatorial change

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9
Q

What phase of meiosis does • Homologous chromosomes enter synapsis?

A

zygotene of prophase I of meiosis I

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10
Q

Describe pachytene of prophase I of meiosis (2)

A
  • Synapsis is complete

* Crossing-over, genetic exchange between nonsister chromatids of a homologous pair, occurs

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11
Q

What phase of meiosis does • Chromosomes thicken and become visible, but the chromatids remain invisible?

A

leptotene of prophase I of meiosis I

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12
Q

What phase of meiosis does  Homologous chromosomes move to opposite poles?

A

anaphase I

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13
Q

What phase:  Chromosomes condense?

A

prophase II

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14
Q

What phase of meiosis does • A tetrad of four chromatids is visible?

A

diplotene of prophase I of meiosis I

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15
Q

What phase of meiosis does  Tetrads line up along the metaphase plate?

A

metaphase I

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16
Q

What phase of meiosis does • The synaptonemal complex forms?

A

zygotene of prophase I of meiosis I

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17
Q

When does each of the two daughter nuclei divides, resulting in four nuclei?

A

meiosis I

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18
Q

Describe telophase II (3)

A

Nuclear membranes re-form, and cytokinesis follows
 Chromosome begins to uncoil
 Cytokinesis- the cytoplasm divides, forming four new haploid cells

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19
Q

What phase:  Sister chromatids attach to spindle fibers from opposite poles?

A

metaphase II

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20
Q

Describe the difference between mitosis and meiosis in term of which cells undergo

A

Mitosis: Haploid and diploid cells can undergo mitosis

Meiosis: Only diploid cells undergo meiosis

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21
Q

Describe zygotene of prophase I of meiosis (2)

A
  • Homologous chromosomes enter synapsis

* The synaptonemal complex forms

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22
Q

What are germ cells?

A

cells destined for a specialized role in the production of gametes

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23
Q

Describe metaphase II (2)

A

chromosomes align at the metaphase plate

 Sister chromatids attach to spindle fibers from opposite poles

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24
Q

What phase of meiosis does • Crossing-over, genetic exchange between nonsister chromatids of a homologous pair, occurs?

A

pachytene of prophase I of meiosis I

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25
Q

How does meiosis contribute to genetic diversity?

A

o Because only chance governs which paternal or maternal homologs migrate to the two poles during the first meiotic division, different gametes carry a different mix of maternal and paternal chromosomes (2n combinations)
o The reshuffling of genetic information through crossing-over during prophase I, ensures an even greater amount of genetic diversity in gametes

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26
Q

What phase:  Chromosome begins to uncoil?

A

telophase II

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27
Q

What phase of meiosis does • Centromeres begin to move toward opposite poles?

A

leptotene of prophase I of meiosis I

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28
Q

Describe the difference between mitosis and meiosis in term of splitting of centromere

A

Mitosis: The centromere splits at the beginning of anaphase

Meiosis: The centromere does not split during meiosis I; The centromere splits at the beginning of anaphase II

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29
Q

What is synapsid chromosome pair containing two chromosomes?

A

bivalent

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30
Q

What phase of meiosis does  The centrome does not divide?

A

anaphase I

31
Q

What phase: Sister chromatids move to opposite spindle poles?

A

anaphase II

32
Q

What phase of meiosis does • Synaptonemal complex dissolves?

A

diplotene of prophase I of meiosis I

33
Q

What is a bivalent?

A

synapsid chromosome pair containing two chromosomes

34
Q

Descibe metaphase I of meiosis (3)

A

 Tetrads line up along the metaphase plate
 Each chromosome of a homologous pair attaches to fibers from opposite poles
 Sister chromatids attach to fibers from the same pole

35
Q

What phase of meiosis does  The chiasmata dissolve?

A

anaphase I

36
Q

What phase of meiosis does • Crossover points appear as chiasmata, holding nonsister chromatids together ?

A

diplotene of prophase I of meiosis I

37
Q

What is crossing over?

A

genetic exchange between nonsister chromatids of a homologous pair

38
Q

Why is meiosis I often called reductional division?

A

o Because the number or chromosomes is reduced to one-half the normal diploid number, meiosis I is often called a reductional division

39
Q

Why is meiosis II called equational division?

A

• Each daughter has the same number of chromosomes as the parental cell present at the beginning of this division; meiosis II termed equational division

40
Q

What phase of meiosis does • Synapsis is complete?

A

pachytene of prophase I of meiosis I

41
Q

What is synapsid chromosome pair containing four chromosomes?

42
Q

Describe the difference between mitosis and meiosis in term of sister chromatids

A

Mitosis: Sister chromatids attach to spindle fibers from opposite poles during metaphase

Meiosis: Homologous chromosomes (not sister chromatids) attach to spindle fibers from opposite poles during metaphase I; Sister chromatids attach to spindle fibers from opposite poles during metaphase II

43
Q

What phase of meiosis does  The nuclear envelope re-forms?

A

telophase I

44
Q

When does the parent nucleus divides to form two daughter nuclei?

45
Q

Describe anaphase II (2)

A

Sister chromatids move to opposite spindle poles

 Centromeres divide

46
Q

Describe the difference between mitosis and meiosis in term of place

A

Mitosis: Occurs in somatic cells

Meiosis: Occurs in germ cells as part of the sexual cycle

47
Q

What phase:  Centrioles move toward the poles?

A

prophase II

48
Q

What is the genetic exchange between nonsister chromatids of a homologous pair?

A

crossing over

49
Q

Describe interkinesis (2)

A

 Similar to interphase except no chromosomal duplication takes place
 In some species, the chromosomes decondense; in others they don’t

50
Q

Describe diplotnene of prophase I of meiosis (4)

A
  • Synaptonemal complex dissolves
  • A tetrad of four chromatids is visible
  • Crossover points appear as chiasmata, holding nonsister chromatids together
  • Meloic arrest occurs at this time in many species
51
Q

What phase:  Centromeres divide?

A

anaphase II

52
Q

Describe the difference between mitosis and meiosis in term of chromosome duplication

A

Mitosis: Mitosis is preceded by S phase (chromosome duplication)

Meiosis: Chromosomes duplicate prior to meiosis I but not before meiosis II

53
Q

What phase of meiosis does • Meloic arrest occurs at this time in many species?

A

diplotene of prophase I of meiosis I

54
Q

Describe the difference between mitosis and meiosis in term of genetic exchange of homologous chromosomes

A

Mitosis: Genetic exchange between homologous chromosomes is very rare

Meiosis: Crossing-over occurs between homologous chromosomes during prophase of meiosis I

55
Q

Describe Anaphase I of meiosis (3)

A

 The centrome does not divide
 The chiasmata dissolve
 Homologous chromosomes move to opposite poles

56
Q

What phase: chromosomes align at the metaphase plate?

A

metaphase II

57
Q

What are the phases of prophase I of meiosis in order? (5)

A 
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
58
Q

Describe prophase I of meiosis

A

Homologs condense and pair, and crossing-over occurs

59
Q

Where does crossing over occur?

A

o Occurs at the recombination nodule which begins to appear along the synaptonemal complex

60
Q

What phase of meiosis does  Each chromosome of a homologous pair attaches to fibers from opposite poles?

A

metaphase I

61
Q

Describe telophase I of meiosis I (2)

A

 The nuclear envelope re-forms

 Resultant cells have half the number of chromosomes, each consisting of two sister chromatids

62
Q

What is non-disjunction?

A

homologs of a chromosomes pair don’t segregate during meiosis I

63
Q

How does sexual fertilization contribute to genetic diversity?

A

o At fertilization, any one of a vast number of genetically diverse sperm can fertilize an egg with its own distinctive genetic constitution

64
Q

Describe the difference between mitosis and meiosis in term of pairing of homologous chromosomes

A

Mitosis: Homologous chromosomes do not pair

Meiosis: During prophase of meiosis I, homologous chromosomes pair (synapse) along their length

65
Q

What is a tetrad?

A

synapsid chromosome pair containing four chromosomes

66
Q

Describe leptotene of prophase I of meiosis (2)

A
  • Chromosomes thicken and become visible, but the chromatids remain invisible
  • Centromeres begin to move toward opposite poles
67
Q

What occurs when the homologs of a chromosomes pair don’t segregate during meiosis I?

A

non-disjunction

68
Q

What are cells destined for a specialized role in the production of gametes?

A

germ cells

69
Q

What happens in meiosis I?

A

the parent nucleus divides to form two daughter nuclei

70
Q

What phase: Nuclear membranes re-form?

A

telophase II

71
Q

What phase:  The nuclear envelope breaks down ?

A

prophase II

72
Q

Describe diakinesis of prophase I of meiosis (2)

A
  • Chromatids thicken and shorten

* At the end of prophase I, the nuclear membrane breaks down and the spindle begins to form

73
Q

What happens in meiosis II?

A

each of the two daughter nuclei divides, resulting in four nuclei

Genetics (62 decks)

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