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Molecular Biology of the Cell > Dr Iqbal Lec 01 Rev 1 > Flashcards

Dr Iqbal Lec 01 Rev 1 Flashcards

1
Q

Which process combines genetic information from two individuals in most eukaryotic organisms for sexual reproduction

A

Sexual reproduction

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2
Q

What is the ploidy level of cells in most sexually reproducing eukaryotic organisms containing two slightly different copies of each chromosome

A

Diploid

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3
Q

Sexual reproduction is dependent on which specialized nuclear division

A

Meiosis

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4
Q

Meiosis produces what type of cells carrying only a single copy of each chromosome

A

Haploid gametes

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5
Q

What are the specialized reproductive cells that haploid cells differentiate into in many organisms

A

Gametes eggs and sperm

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6
Q

The fusion of a sperm and egg cell forms a diploid cell called a what which can form a genetically distinct individual

A

Zygote

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7
Q

How many rounds of chromosome segregation does meiosis include unlike mitosis

A

Two

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8
Q

Meiosis reduces the chromosome number by how much

A

Half

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9
Q

In which phase of meiosis does the cell duplicate its chromosomes resulting in sister chromatids

A

Meiotic S phase

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10
Q

Sister chromatids are tightly linked along their entire lengths by what complexes

A

Cohesin complexes

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11
Q

What substance is made up of DNA or RNA and proteins like histones and condenses during cell division to become a chromosome

A

Chromatin

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12
Q

Which are highly packaged and more condensed during cell division chromatins or chromosomes

A

Chromosomes

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13
Q

Meiosis begins with a single round of what

A

Chromosome duplication

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14
Q

In meiosis I what structures pair up and are segregated into different daughter nuclei

A

Duplicated homologs

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15
Q

What occurs during meiosis I as indicated by the formation of chromosomes that are partly red and partly gray in the diagram

A

Genetic recombination crossing-over

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16
Q

In meiosis II what structures are segregated

A

Sister chromatids

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17
Q

During early prophase I of meiosis what process involves homologs associating along their length

A

Pairing

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18
Q

Pairing of homologs may begin with interactions between what complementary DNA sequences

A

Pairing sites

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19
Q

The gradual juxtaposition of homologs occurs during which prolonged period

A

Prophase I

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20
Q

As prophase I progresses homologs become more closely aligned forming a four-chromatid structure called a what

A

Bivalent

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21
Q

What protein matrix usually joins homologs at the bivalent stage

A

Synaptonemal complex

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22
Q

What is the function of the synaptonemal complex SC

A

Stabilizes the pairing of homologs and promotes crossover recombination

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23
Q

SC promotes and regulates crossover recombination which results in what physical linkages between homologous chromosomes

A

Chiasmata

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24
Q

What are the physical linkages between homologous chromosomes that persist until segregation and mediate bipolar alignment on the spindle

A

Chiasmata

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25
Q

Following the formation of a bivalent how are homolog pairs locked together

A

Homologous recombination

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26
Q

DNA double-strand breaks are formed at several locations in each sister chromatid resulting in DNA recombination events between which structures

A

Homologs

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27
Q

Reciprocal DNA exchanges where DNA of a chromatid crosses over to become continuous with DNA of a homologous chromatid are called what

A

Crossovers

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28
Q

Each homolog is organized around a protein what during pairing

A

Axial core

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29
Q

The synaptonemal complex forms when homolog axes are linked by what rod-shaped structures

A

Rod-shaped transverse filaments

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30
Q

The axial core of each homolog interacts with what complexes that hold sister chromatids together

A

Cohesin complexes

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31
Q

A recombination complex assembles on a double-strand break in a chromatid and binds the matching DNA sequence in the nearby homolog helping to reel in this partner in what process

A

Presynaptic alignment

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32
Q

Following presynaptic alignment what process involves the axial core of a homolog becoming tightly linked to the axial core of its partner by transverse filaments creating a synaptonemal complex

A

Synapsis

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33
Q

What is seen microscopically as a thin connection between homologs where a single crossover has occurred between nonsister chromatids

A

Chiasma

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34
Q

Where do DNA double-strand breaks tend to cluster in meiosis I

A

Hot spots where DNA is accessible

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35
Q

Where do DNA double-strand breaks occur only rarely in meiosis I

A

Cold spots such as heterochromatin regions around centromeres and telomeres

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36
Q

What is one important contribution of crossovers

A

Contributes to genetic diversification of gametes

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37
Q

What regulates the location and number of crossovers that form

A

At least two kinds of regulation operating before SC assembles

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38
Q

What ensures that at least one crossover forms between members of each homolog pair necessary for normal homolog segregation in meiosis I

A

A type of regulation on crossover formation

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39
Q

What phenomenon is where the presence of one crossover event inhibits another from forming close by

A

Crossover interference

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40
Q

What must homologous chromosomes do during meiosis to segregate accurately

A

Pair synapse and undergo crossover recombination

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41
Q

Meiotic prophase is divided into how many sequential stages based on morphological changes during homolog pairing

A

Five

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42
Q

Which stage of meiotic prophase I is when homologs condense and pair and genetic recombination begins

A

Leptotene

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43
Q

At which stage of meiotic prophase I does the synaptonemal complex begin to assemble

A

Zygotene

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44
Q

At which stage of meiotic prophase I is the assembly of the synaptonemal complex complete and homologs are synapsed along their entire lengths

A

Pachytene

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45
Q

Which stage of meiotic prophase I can persist for days or longer until desynapsis begins

A

Pachytene

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46
Q

At which stage of meiotic prophase I does desynapsis begin with the disassembly of the synaptonemal complexes

A

Diplotene

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47
Q

At which stage of meiotic prophase I can individual crossover events between nonsister chromatids be seen as inter-homolog connections called chiasmata

A

Diplotene

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48
Q

What promotes chromosome pairing synapse and recombination during meiosis according to the text

A

Nuclear envelope NE-associated chromosome dynamics

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49
Q

What is a fundamental difference between meiosis I and mitosis and meiosis II regarding segregation

A

Separation and segregation of homologs rather than sister chromatids

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50
Q

In meiosis I both sister kinetochores in a homolog must attach stably to which spindle pole

A

The same spindle pole

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51
Q

What is the primary purpose of meiosis in sexually reproducing organisms?

A

To produce haploid gametes

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52
Q

How does meiosis differ from mitosis in terms of division rounds?

A

Meiosis has two rounds whereas mitosis has one

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53
Q

What occurs during the meiotic S phase?

A

Chromosomes duplicate forming sister chromatids

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54
Q

What structure links sister chromatids after chromosome duplication?

A

Cohesin complexes

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55
Q

What happens to homologous chromosomes during Meiosis I?

A

They pair up and segregate into different nuclei

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56
Q

What process in Meiosis I increases genetic diversity?

A

Crossing-over

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57
Q

What is the outcome of Meiosis II?

A

Segregation of sister chromatids into haploid cells

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58
Q

What are the five stages of Prophase I in meiosis?

A

Leptotene zygotene pachytene diplotene diakinesis

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59
Q

What is the role of the synaptonemal complex in meiosis?

A

Stabilizes homolog pairing and promotes crossovers

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60
Q

What are chiasmata observed in Prophase I?

A

Physical linkages from crossovers between homologs

61
Q

What initiates genetic recombination in Prophase I?

A

DNA double-strand breaks

62
Q

How many chromatids are present in a bivalent?

63
Q

What ensures at least one crossover per homolog pair?

A

Crossover regulation

64
Q

What prevents multiple crossovers from occurring close together?

A

Crossover interference

65
Q

What feature of Meiosis I allows homologs to segregate?

A

Sister kinetochores attach to the same spindle pole

66
Q

What protects centromeric cohesin during Meiosis I?

67
Q

What is the result of sperm and egg fusion?

A

A diploid zygote

68
Q

What can nondisjunction during meiosis lead to?

A

Gametes with abnormal chromosome numbers

69
Q

What condition results from an extra chromosome 21?

A

Down syndrome

70
Q

What increases the likelihood of segregation errors in female meiosis?

A

Advancing maternal age

71
Q

What does the diagram of homologous chromosomes on page 19 illustrate?

A

Structure including telomeres centromere and sister chromatids

72
Q

What is depicted in the light micrograph of a grasshopper bivalent?

A

A bivalent with chiasmata

73
Q

What does the electron micrograph on page 67 show?

A

Synaptonemal complex at pachytene

74
Q

What indicates incomplete synapsis in the immunofluorescence image?

A

Red arrowheads

75
Q

What begins the pairing of homologs in early Prophase I?

A

Interactions between complementary DNA sequences

76
Q

What structure forms between homologs during pachytene?

A

Synaptonemal complex

77
Q

What becomes visible after synaptonemal complex disassembly?

78
Q

What is the purpose of chromosome condensation in diplotene?

A

Prepares homologs for segregation

79
Q

What connects chromosomes to spindle microtubules?

A

Kinetochores

80
Q

What is the fate of cohesin along chromosome arms in Anaphase I?

A

It is cleaved

81
Q

How do sister kinetochores behave in mitosis differently from Meiosis I?

A

They attach to opposite spindle poles

82
Q

What is the consequence of homologs failing to separate in meiosis?

A

Nondisjunction

83
Q

What are the specialized reproductive cells produced by meiosis?

A

Eggs and sperm

84
Q

What does chromatin condense into during cell division?

A

Chromosomes

85
Q

What is the role of the nuclear envelope in meiosis?

A

Promotes chromosome pairing and recombination

86
Q

How many chromatids must a human cell track during meiosis?

87
Q

What is a common cause of spontaneous abortion in humans?

A

Chromosome segregation errors

88
Q

What stage marks the completion of synaptonemal complex assembly?

89
Q

What occurs at leptotene in Prophase I?

A

Homologs condense and begin pairing

90
Q

What process follows presynaptic alignment of homologs?

91
Q

What are hot spots in the context of crossing-over?

A

Regions where DNA is accessible for breaks

92
Q

What are cold spots in chromosomal DNA?

A

Heterochromatin regions with rare crossovers

93
Q

What mediates bipolar alignment of homologs on the spindle?

94
Q

What protein complex holds sister chromatids together?

95
Q

What enzyme cleaves cohesin in anaphase?

96
Q

What is the significance of crossovers in gamete production?

A

Increases genetic diversity

97
Q

What type of division does Meiosis II resemble?

98
Q

What ensures sister chromatids remain together until Meiosis II?

A

Centromeric cohesin

99
Q

What is the primary difference between Meiosis I and Meiosis II?

A

Homologs segregate in I sister chromatids in II

100
Q

What triggers homolog separation at Anaphase I?

A

Loss of arm cohesion

101
Q

What does the diagram of a bivalent with three chiasmata show?

A

Multiple crossover events

102
Q

What is the arrangement of crossovers in the drawing on page 48?

A

Exchanges between specific chromatids

103
Q

What are the components of the synaptonemal complex?

A

Protein matrix and transverse filaments

104
Q

What does the recombination complex bind to during crossing-over?

A

Matching DNA sequence in the homolog

105
Q

What is the state of homologs at diakinesis?

A

Condensed and ready for segregation

106
Q

What indicates a crossover microscopically?

107
Q

What is the total number of chromosomes in a human diploid cell?

108
Q

What is the ploidy of gametes produced by meiosis?

109
Q

What process divides the cytoplasm after nuclear division?

A

Cytokinesis

110
Q

What is the outcome of cytokinesis in meiosis?

A

Four haploid cells

111
Q

What does the cohesin complex interact with in homologs?

A

Axial core

112
Q

What stage begins the disassembly of the synaptonemal complex?

113
Q

What is the role of kinetochore-associated proteins in Meiosis I?

A

Ensure sister chromatids attach to the same pole

114
Q

What happens to sister chromatids at Anaphase II?

A

They separate

115
Q

How does sexual reproduction mix genetic information?

A

Combines genomes of two parents

116
Q

What is the structure of chromatin before condensation?

A

Unwound DNA and proteins

117
Q

What occurs during zygotene in Prophase I?

A

Synaptonemal complex assembly begins

118
Q

What is the consequence of errors in egg development?

A

Spontaneous abortion or mental retardation

119
Q

What allows homologs to be pulled apart in Meiosis I?

A

Resolution of crossovers

120
Q

What is the function of transverse filaments in the synaptonemal complex?

A

Link homolog axes

121
Q

What does the diagram on page 66 represent?

A

A single bivalent schematically

122
Q

What is the chromosome number in a human haploid gamete?

123
Q

What process locks homolog pairs together in Prophase I?

A

Homologous recombination

124
Q

What is the significance of bi-orientation in Meiosis I?

A

Allows homolog segregation

125
Q

What persists until segregation in Meiosis I?

126
Q

What type of DNA exchanges occur in crossovers?

A

Reciprocal

127
Q

What maintains sister chromatid cohesion at centromeres in Meiosis I?

128
Q

What is the leading cause of mental retardation mentioned in the PDF?

A

Down syndrome

129
Q

What stage follows pachytene in Prophase I?

130
Q

What is the role of axial cores in homolog pairing?

A

Organize chromatin loops

131
Q

What does the immunofluorescence image on page 67 illustrate?

A

Partially synapsed bivalents

132
Q

What ensures proper homolog segregation in Meiosis I?

A

At least one crossover per pair

133
Q

What is the fate of the starting cell’s chromatids in meiosis?

A

Distributed to four haploid progeny

134
Q

What increases genetic recombination during Meiosis I?

A

Homolog pairing

135
Q

What is the structure formed by paired homologs in Prophase I?

136
Q

What does the PDF recommend reading for further study?

A

Molecular Biology of the Cell 6th Edition

137
Q

What is the email address of the unit leader?

A

miq.quresh@gmail.com

138
Q

Who is the unit leader for this lecture series?

A

Dr. Muhammad Iqbal Qureshi

139
Q

What are the two main topics covered in the lecture series?

A

Meiosis and cytokinesis with cell division control

140
Q

What begins the meiotic program in the cell cycle?

A

Chromosome duplication

141
Q

What is the state of chromosomes after the meiotic S phase?

A

Duplicated with sister chromatids

142
Q

What does the PDF compare Meiosis II to in the summary?

143
Q

What ensures homologs stay connected at centromeres in Anaphase I?

A

Kinetochore-associated proteins

144
Q

What is the consequence of nondisjunction in Meiosis I?

A

Abnormal chromosome distribution

145
Q

What is the purpose of cohesin cleavage in Anaphase I?

A

Resolves crossovers for homolog separation

146
Q

What indicates the start of genetic recombination in leptotene?

A

Homolog condensation

147
Q

What is the final product of meiosis in many organisms?

148
Q

What does the PDF state about diploid cells?

A

They contain two homologs of each chromosome

149
Q

What promotes accurate segregation of homologs in meiosis?

A

Pairing synapsis and recombination

Molecular Biology of the Cell (19 decks)

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