Chapter 4.4: Meiosis: Cell Divisions That Halve Chromosome Number

Question 1

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

Answer 1

diakinesis of prophase I of meiosis I

Question 2

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

Answer 2

metaphase I

Question 3

What are somatic cells?

Answer 3

• 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

Question 4

Describe prophase II (3)

Answer 4

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

Question 5

What phase:  Cytokinesis?

Answer 5

telophase II

Question 6

What phase of meiosis does • Chromatids thicken and shorten?

Answer 6

diakinesis of prophase I of meiosis I

Question 7

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

Answer 7

Mitosis: One round of division

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

Question 8

Describe the difference between mitosis and meiosis in term of products

Answer 8

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

Question 9

What phase of meiosis does • Homologous chromosomes enter synapsis?

Answer 9

zygotene of prophase I of meiosis I

Question 10

Describe pachytene of prophase I of meiosis (2)

Answer 10

• Synapsis is complete

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

Question 11

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

Answer 11

leptotene of prophase I of meiosis I

Question 12

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

Answer 12

anaphase I

Question 13

What phase:  Chromosomes condense?

Answer 13

prophase II

Question 14

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

Answer 14

diplotene of prophase I of meiosis I

Question 15

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

Answer 15

metaphase I

Question 16

What phase of meiosis does • The synaptonemal complex forms?

Answer 16

zygotene of prophase I of meiosis I

Question 17

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

Answer 17

meiosis I

Question 18

Describe telophase II (3)

Answer 18

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

Question 19

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

Answer 19

metaphase II

Question 20

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

Answer 20

Mitosis: Haploid and diploid cells can undergo mitosis

Meiosis: Only diploid cells undergo meiosis

Question 21

Describe zygotene of prophase I of meiosis (2)

Answer 21

• Homologous chromosomes enter synapsis

* The synaptonemal complex forms

Question 22

What are germ cells?

Answer 22

cells destined for a specialized role in the production of gametes

Question 23

Describe metaphase II (2)

Answer 23

chromosomes align at the metaphase plate

 Sister chromatids attach to spindle fibers from opposite poles

Question 24

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

Answer 24

pachytene of prophase I of meiosis I

Question 25

How does meiosis contribute to genetic diversity?

Answer 25

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

Question 26

What phase:  Chromosome begins to uncoil?

Answer 26

telophase II

Question 27

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

Answer 27

leptotene of prophase I of meiosis I

Question 28

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

Answer 28

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

Question 29

What is synapsid chromosome pair containing two chromosomes?

Answer 29

bivalent

Question 30

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

Answer 30

anaphase I

Question 31

What phase: Sister chromatids move to opposite spindle poles?

Answer 31

anaphase II

Question 32

What phase of meiosis does • Synaptonemal complex dissolves?

Answer 32

diplotene of prophase I of meiosis I

Question 33

What is a bivalent?

Answer 33

synapsid chromosome pair containing two chromosomes

Question 34

Descibe metaphase I of meiosis (3)

Answer 34

 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

Question 35

What phase of meiosis does  The chiasmata dissolve?

Answer 35

anaphase I

Question 36

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

Answer 36

diplotene of prophase I of meiosis I

Question 37

What is crossing over?

Answer 37

genetic exchange between nonsister chromatids of a homologous pair

Question 38

Why is meiosis I often called reductional division?

Answer 38

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

Question 39

Why is meiosis II called equational division?

Answer 39

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

Question 40

What phase of meiosis does • Synapsis is complete?

Answer 40

pachytene of prophase I of meiosis I

Question 41

What is synapsid chromosome pair containing four chromosomes?

Answer 41

tetrad

Question 42

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

Answer 42

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

Question 43

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

Answer 43

telophase I

Question 44

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

Answer 44

meiosis I

Question 45

Describe anaphase II (2)

Answer 45

Sister chromatids move to opposite spindle poles |  Centromeres divide

Question 46

Describe the difference between mitosis and meiosis in term of place

Answer 46

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

Question 47

What phase:  Centrioles move toward the poles?

Answer 47

prophase II

Question 48

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

Answer 48

crossing over

Question 49

Describe interkinesis (2)

Answer 49

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

Question 50

Describe diplotnene of prophase I of meiosis (4)

Answer 50

* 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

Question 51

What phase:  Centromeres divide?

Answer 51

anaphase II

Question 52

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

Answer 52

Mitosis: Mitosis is preceded by S phase (chromosome duplication) Meiosis: Chromosomes duplicate prior to meiosis I but not before meiosis II

Question 53

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

Answer 53

diplotene of prophase I of meiosis I

Question 54

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

Answer 54

Mitosis: Genetic exchange between homologous chromosomes is very rare Meiosis: Crossing-over occurs between homologous chromosomes during prophase of meiosis I

Question 55

Describe Anaphase I of meiosis (3)

Answer 55

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

Question 56

What phase: chromosomes align at the metaphase plate?

Answer 56

metaphase II

Question 57

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

Answer 57

``` Leptotene Zygotene Pachytene Diplotene Diakinesis ```

Question 58

Describe prophase I of meiosis

Answer 58

Homologs condense and pair, and crossing-over occurs

Question 59

Where does crossing over occur?

Answer 59

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

Question 60

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

Answer 60

metaphase I

Question 61

Describe telophase I of meiosis I (2)

Answer 61

 The nuclear envelope re-forms |  Resultant cells have half the number of chromosomes, each consisting of two sister chromatids

Question 62

What is non-disjunction?

Answer 62

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

Question 63

How does sexual fertilization contribute to genetic diversity?

Answer 63

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

Question 64

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

Answer 64

Mitosis: Homologous chromosomes do not pair Meiosis: During prophase of meiosis I, homologous chromosomes pair (synapse) along their length

Question 65

What is a tetrad?

Answer 65

synapsid chromosome pair containing four chromosomes

Question 66

Describe leptotene of prophase I of meiosis (2)

Answer 66

* Chromosomes thicken and become visible, but the chromatids remain invisible * Centromeres begin to move toward opposite poles

Question 67

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

Answer 67

non-disjunction

Question 68

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

Answer 68

germ cells

Question 69

What happens in meiosis I?

Answer 69

the parent nucleus divides to form two daughter nuclei

Question 70

What phase: Nuclear membranes re-form?

Answer 70

telophase II

Question 71

What phase:  The nuclear envelope breaks down ?

Answer 71

prophase II

Question 72

Describe diakinesis of prophase I of meiosis (2)

Answer 72

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

Question 73

What happens in meiosis II?

Answer 73

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