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MOL BIO Exam #1- Lo > Lec 06- Meiosis, Germ Cells, and Fertilization > Flashcards

Lec 06- Meiosis, Germ Cells, and Fertilization Flashcards

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1
Q

Contains 2 sets of chromosomes, one from each parent

A

diploid

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2
Q

Contains 1 set of chromosomes

A

haploid

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3
Q

Specialized reproductive cells; sperm or eggs generated through meiosis

A

gametes

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4
Q

Process by which haploid gametes fuse to form a diploid cell (zygote)

A

fertilization

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5
Q

How does a zygote divide to become a multicellular organism?

A

divides by mitosis

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6
Q

What are germline cells?

A

gametes and their precursors

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7
Q

What cells form the rest of the body and leave no progeny?

A

somatic cells

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8
Q

What are autosomes?

A
  • chromosomes common to both sexes

- one from each parent in each diploid nucleus

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9
Q

What are the 2 sex chromosomes?

A

X and Y

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10
Q

What are 2 ways that meiosis creates genetic diversity?

A
  • random segregation of homologs during meiosis

- crossing over

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11
Q

Gametes are ______

A

haploid

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12
Q

Gametes arise from meiosis which involved _______ cell divisions and ______ round of DNA synthesis to produce __________ the number of chromosomes

A
  • 2 divisions
  • 1 round of DNA synthesis
  • half number of chromosomes
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13
Q

When do the chromosomes replicate during meiosis I?

A

S-phase

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14
Q

What binds the 2 sister chromatids in meiosis I?

A

cohesion complexes

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15
Q

What happens to homologs during meiosis I?

A

They pair, recombine, and separate in meiosis I

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16
Q

Is there DNA replication in meiosis II?

A

NO

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17
Q

What happens to sister chromatids in meiosis II?

A

sister chromatids = divided (Anaphase II)

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18
Q

What is the result of meiosis II?

A

4 haploid daughter cells

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19
Q

What happens to the homologs in prophase I of meiosis?

A

homologs begin to pair

lasts days/weeks

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20
Q

What is a bivalent?

A

the structure of 4 chromatids in prophase I of meiosis

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21
Q

What is required for stable pairing of homologs in prophase I of meiosis?

A

crossing over at the chiasma

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22
Q

What protein structure joins homologs in prophase I of meiosis?

A

synaptonemal complex

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23
Q

What is the pseudoautosomal region?

A
  • small region of homology between X and Y
  • allows X and Y to pair
  • prophase I of meiosis
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24
Q

What are the 5 phases of prophase of meiosis?

A
  • Leptotene
  • Zygotene
  • Pachytene
  • Diplotene
  • Diakinesis
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25
Q

What happens in the Leptotene phase of prophase?

A

homologs begin to condense/pair

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26
Q

What happens in the Zygotene phase of prophase?

A
  • homologs pair

- synaptonemal complexes form

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27
Q

What happens in the Pachytene phase of prophase?

A
  • synapsis is complete

- crossing over occurs

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28
Q

What happens in the Diplotene phase of prophase?

A
  • synaptonemal complex begins to break down

- homologs begin to separate but remain attached at chiasmata

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29
Q

What happens in the Diakinesis phase of prophase?

A
  • reach max condensation
  • separation of homologs
  • transition stage into metaphase
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30
Q

What is the synaptonemal complex made of?

A

transverse filaments between homologs

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31
Q

What is the synaptonemal complex important for?

A

crossing over

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32
Q

When do cohesion complexes assemble on the DNA?

A

during S-phase

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33
Q

What do the cohesion complexes bind to when they assemble on DNA?

A

bind sister chromatids

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34
Q

What is the function of cohesion complexes?

A
  • major component of axial core of each homolog

- play important role in segregating homologs in meiosis I

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35
Q

Where do kinetochores attach?

A

on the 2 sister chromatids to the microtubules coming from the same pole

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36
Q

What phase of meiosis do homologs separate at?

A

anaphase I

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37
Q

When do the arms of sister chromatids separate in meiosis?

A

anaphase I

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38
Q

What can occur when the arms of sister chromatids separate in meiosis?

A
  • chiasmata resolved

- allows homologs to separate

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39
Q

When do sister chromatids separate in anaphase II of meiosis?

A

when separate cleaves cohesion complexes

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40
Q

What happens when human female meiosis is arrested for years after diplotene?

A
  • Meiosis I = completed only at ovulation

- Meiosis II = completed after fertilization

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41
Q

What is nondisjunction?

A

when homologs fail to separate properly

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42
Q

When are nondisjunction errors common?

A

during egg development

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43
Q

What happens to nondisjunction errors with age?

A

increase errors with age

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44
Q

What is the leading cause of spontaneous abortions/mental retardation in humans?

A

nondisjunction

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45
Q

What are aneuploid errors?

A

cells with abnormal chromosome number

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46
Q

What is the most common single cause of mental retardation?

A

Trisomy 21

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47
Q

In 90% of trisomy 21 individuals, the additional chromosome is from what origin?

A

maternal

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48
Q

What % of trisomy 21 occurs in meiosis I and meiosis II?

A

70% in meiosis I

30% in meiosis II

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49
Q

What does euploid mean?

A

cells with normal number of chromosomes

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50
Q

How man different gametes can random distribute of maternal/paternal homologs produce?

A

2^n

2^23 = 8.4x10^6

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51
Q

What increases genetic variation?

A

crossing over

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52
Q

How many crossovers occur per human homolog?

A

2-3

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53
Q

When do female mammals being meiosis?

A

in fetal ovary

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54
Q

When is meiosis I completed for female mammals?

A

at ovulation (until about 40 years later)

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55
Q

When is meiosis II completed for female mammals?

A

only at fertilization

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56
Q

When do male mammals begin meiosis?

A

at puberty (in the testes)

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57
Q

When is meiosis completed for male mammals?

A

24 days (proceeds without arrest)

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58
Q

What % of eggs are aneuploid?

A

20%

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59
Q

What % of sperm is aneuploid?

A

3-4%

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60
Q

What leads to apoptosis of abnormal sperm?

A

a cell cycle checkpoint that is activated in sperm with meiotic errors

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61
Q

What % of all human conceptions are aneuploid?

A

25%

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62
Q

What is human aneuploid due mostly to?

A

nondisjunction in oocytes at meiosis I

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63
Q

Which gametes are more prone to new DNA mutations?

A

male gametes

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64
Q

Why are male gametes more prone to new DNA mutations?

A

they undergo more mitotic cell divisions

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65
Q

What does advanced paternal age lead to?

A

increased risk of point mutations in male gametes

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66
Q

Where are primordial germ cells (PGCs) found? What do they give rise to?

A
  • found in all vertebrate embryos

- give rise to gametes

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67
Q

Where do the PGCs migrate to?

A

the developing gonads (ovaries/testes)

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68
Q

What do PGCs proliferate through?

A

mitosis then meiosis to differentiate into haploid gametes (sperm/egg)

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69
Q

What is different in some animal eggs compared to mammals?

A

some animal eggs contain specific molecules that determine which cells become germ cells

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70
Q

What do mammals rely on?

A

rely on neighboring cell signals to dictate which cells become PGCs

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71
Q

What is unique about the mammal dividing egg?

A
  • it is totipotent for the first few rounds of cell division

- then it differentiates into PGCs

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72
Q

What suppresses somatic cell fates in mammals?

A

gene repression

Translation of certain RNAs must be inhibited (Nanos)

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73
Q

How is the genital ridge formed?

A

cell signaling leads to proliferation and migration of PGCs to the developing gonad

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74
Q

Are PGCs committed to their cell fate?

A

NO, they are pluripotent

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75
Q

What does pluripotent mean?

A

cells can be removed and cultured with signaling proteins to form cell lines for any type of cell for the body except extraembryonic cells

76
Q

What determines if the gonad is ovary or testes?

A

the sex chromosomes in the genital ridge

NOT the sex chromosomes in the PGC

77
Q

Are X patients with 45 chromosomes male or female?

A

female

78
Q

What does the Y chromosome do?

A

directs genital ridge to develop into testis

79
Q

What is the default sex determination pathway?

A

female

80
Q

What is SRY?

A

sex determining region of Y

81
Q

What is the function of the SRY gene?

A

necessary and sufficient for testis development in mammals

82
Q

What can SRY gene cause?

A

sex-reversal

83
Q

What will the XX mouse + SRY develop as?

A

male (sterile)

84
Q

What will the XY male with inactivating SRY mutation develop as?

A

female

85
Q

What does the expression of SRY cause?

A

cells to differentiate into Sertoli cells

86
Q

What are sertoli cells?

A

testis support cells

87
Q

What does SRY encode?

A

Sox9

88
Q

What is Sox9?

A
  • DNA binding protein that regulates transcription of genes involved in Sertoli development
  • expressed in all vertebrates
89
Q

What does Sox9 activate?

A

-activates Sertoli-specific genes (including anti-Mullertian hormone)

90
Q

What results from ectopic expression of Sox9 in developing XX mouse gonads?

A

causes them to develop as males (even without SRY)

91
Q

What does SRY do in somatic cells?

A
  • directs differentiation into Sertoli cells instead of follicle cells
  • induce Leydig cell differentiation
92
Q

What do Sertoli cells secrete?

A

anti-Mullerian hormone

93
Q

What does anti-Mullerian hormone do?

A
  • suppresses female development

- causes Mullerian duct to regress

94
Q

What does the induction of Leydig cell differentiation do?

A

Secretes testosterone

95
Q

What is the function of testosterone secreted from Leydig cells?

A

responsible for secondary sexual characteristics

96
Q

What happens to gonadal development in the absence of SRY?

A
  • genital ridge becomes an ovary
  • PGC becomes an egg
  • Somatic cells differentiate differently
97
Q

What do the somatic cells differentiate into when there is no SRY?

A
  • Follicle cells (support cells)

- Theca cells (estrogen-producing cells)

98
Q

What triggers egg activation?

A

fertilization (fusion of sperm and egg)

99
Q

What is parthenogentic activation?

A

activation in absence of sperm

100
Q

In what animals does parthenogentic activation occur?

A

some lizards and frogs

101
Q

Why can’t mammals do parthenogentic activation?

A

due to imprinting

102
Q

What can the egg cytoplasm be used for?

A

can be used to reprogram a somatic cell nucleus to direct development of a new individual

REPRODUCTIVE CLONING

103
Q

What is the nutritional reserve for eggs?

A

yolk sac

104
Q

What is the yolk sac made of?

A
  • lipids
  • proteins
  • polysaccharides
105
Q

What are yolk granules?

A

discrete yolk-containing structures

106
Q

What is the egg coat?

A

a glycoprotein-rich extracellular matrix

107
Q

What does the egg coat do?

A
  • protects from mechanical damage

- acts as species-specific barrier to sperm

108
Q

What is the egg coat called in mammals vs. non-mammalian eggs?

A

mammals = Zona pellucida

non-mammals = Vitelline layer

109
Q

What happens upon egg activation?

A
  • corticle granules release their contents
  • contents enter egg coat
  • block polyspermy
110
Q

What are cortical granules?

A

specialized secretory cells

111
Q

What are the stages of oogenesis?

A

1) Primordial germ cells migrate into gonad
2) Diploid oogonia undergo mitotic cell divisions then enter meiosis
3) Primary oocytes arrest at prophase I of meiosis I
4) Progression resumes at ovulation
5) Cytoplasm divides asymmetrically
6) Secondary oocyte arrested at metaphase II
7) Meiosis completed after fertilization

112
Q

When are primary oocytes formed?

A

during gestation of human embryo

113
Q

What results from the cytoplasm’s asymmetrical division?

A
  • small polar body

- large secondary oocyte

114
Q

How do eggs achieve large size?

A

-have extra gene copies in the cell

115
Q

When does egg growth occur?

A

after DNA replication

116
Q

Some species produce many copies of some genes like ______

A

rRNA

117
Q

How are yolk proteins imported?

A

through receptor-mediated endocytosis

118
Q

What do accessory cells (like nurse cells) do?

A
  • make ribosomes, mRNA, and proteins

- transport into oocyte (insect)

119
Q

What do follicle cells connect to?

A

connect to each other and oocyte

120
Q

How do follicle cells communicate?

A

though gap junctions

121
Q

What is the primordial follicle?

A

oocyte surrounded by single layer of follicle cells

122
Q

What are developing follicles?

A

multiple layers of follicle cells (granulosa cells) surrounding growing oocyte

123
Q

What do some developing follicles acquire?

A

antrum (fluid-filled cavity)

124
Q

What happens at puberty?

A

FSH surge induces antral follicles (one becomes dominant)

125
Q

What triggers ovulation?

A

FSH + LH in the middle of menstrual cycle

126
Q

What triggers primary oocyte to complete meiosis I?

A

FSH + LH in the middle of menstrual cycle

127
Q

When is the secondary ooctye released (still surrounded by granulosa cells)?

A

when the follicle enlarges and ruptures

128
Q

When does the secondary oocyte complete meiosis II?

A

only when fertilized

129
Q

Why are sperm smaller than the egg?

A

optimized to carry DNA to the egg

130
Q

Do sperm have cytoplasmic organelles?

A

NO

They have stripped down cells

131
Q

What are the 2 distinct regions of sperm?

A
  • Head (nucleus)

- Tail (propulsion)

132
Q

What is the mid piece of sperm packed with?

A

mitochondria

to power flagellum for movement

133
Q

What do the dyenin motor proteins require in order to slide microtubules for sperm movement?

A

ATP hydrolysis

134
Q

What enzymes does the acrosomal vesicles contain?

A

hydrolytic enzymes

135
Q

What releases the hydrolytic enzyme?

A

released by exocytosis in acrosome reaction

136
Q

What does hydrolytic enzyme do?

A

helps penetrate egg’s outer coat

137
Q

What results when primary spermatocytes complete meiosis I?

A

produce 2 secondary spermatocytes with 22 duplicated autosomes and X or Y

138
Q

What does each secondary spermatocyte produce after going through meiosis II?

A

4 haploid spermatids

139
Q

What do the 4 haploid spermatids differentiate into?

A

sperm

140
Q

What do sperm escape into?

A

the lumen of seminiferous tubule

141
Q

What happens in the epididymis?

A

sperm pass through it and are stored and undergo further maturation

142
Q

Where does spermatogenesis occur?

A

in seminiferous tubules

143
Q

What do the seminiferous tubules maintain close contact with?

A

sertoli cells

144
Q

Spermatogonia undergo ______ mitotic divisions before entering meiosis I

A

limited

145
Q

What happens to progeny of spermatogonium since they don’t complete cytokinesis?

A

they remain connected through synctium

146
Q

What are synctium?

A

cytoplasmic bridges that connect progeny of spermatogonium

147
Q

The progeny of spermatogonium each share a common ________

A

cytoplasm

148
Q

Sperm are produced in _________ batches

A

synchronous

149
Q

What do sperm have access to for their development?

A

diploid genome

150
Q

Order or sperm production

A
  • spermatogonium (mitosis) (46)
  • spermatogonia
  • primary spermatocytes (meiosis I)
  • secondary spermatocytes (meiosis II)
  • spermatids (23)
  • differentiating spermatids
  • mature spermatozoa + residual bodies
151
Q

What is capacitation?

A

process required to acquire capacity to fertilize an egg

152
Q

How long does fertilization take in humans?

A

5-6 hours

153
Q

Where is fertilization completed?

A

in oviduct

154
Q

Why do sperm undergo many biochemical and functional changes during fertilization?

A
  • increases motility of flagellum

- makes sperm capable of undergoing acrosome reaction

155
Q

What are the requirements for fertilization?

A
  • Albumin
  • Calcium
  • HCO3
156
Q

Where are all the requirements for fertilization located?

A

in female genital tract

157
Q

What is the function of albumin for fertilization?

A
  • helps extract cholesterol from membrane

- increases membrane ability to fuse with acrosome membrane

158
Q

What is the function of calcium and HCO3 for fertilization?

A

activate adenyl cyclase in sperm to produce cAMP

-helps initiate capacitation-associated changes

159
Q

What is the released egg surrounded by?

A
  • granulosa cells

- hyaluronic acid rich ECM

160
Q

How do the capacitated sperm penetrate granulosa cells?

A

hyaluronidase

161
Q

What happens when the sperm binds to the zone pellucida?

A

zona pellucida acts as a species barrier

162
Q

What is the function of the zona pellucida?

A

-induces sperm to undergo acrosome reaction

163
Q

What does the acrosome reaction do?

A

alters sperm so it can bind and fuse with plasma membrane of egg

164
Q

What do the contents of the acrosome reaction do to help the sperm?

A

help sperm tunnel through zona pellucida

165
Q

How does the sperm bind to the egg plasma membrane?

A 
1st = tip
2nd = side
166
Q

What aids in the process of the sperm binding to the egg?

A

microvilli on the egg

167
Q

What membrane proteins are crucial to the egg and sperm binding?

A

ZP1
ZP2
ZP3

168
Q

Which membrane proteins form long filaments?

A

ZP2

ZP3

169
Q

Which membrane protein cross-links the filaments?

A

ZP1

170
Q

Steps of fertilization

A

1) binding of sperm to zona pellucida
2) acrosome reaction
3) penetration through zona pellucida
4) fusion of plasma membranes
5) sperm contents enter egg cytoplasm

171
Q

What does fusion of an egg and a sperm (egg activation) induce?

A
  • cortical reaction (cortical granules release contents)

- meiosis to resume

172
Q

How are the cortical reaction and meiosis resumption triggered?

A

increased calcium in the cytosol

173
Q

What can egg activation be artificially triggered by?

A
  • injecting calcium into the egg

- fused sperm or injection of sperm, a sperm head, or sperm extract into the egg

174
Q

Fusion of sperm causes change in egg plasma membrane so other sperm can’t fuse. What is this called?

A

inhibition of polyspermy

175
Q

What happens to ZP3 when cortical reaction occurs?

A

ZP3 = inactivated

cannot bind sperm or induce acrosome reaction

176
Q

What happens to ZP2 when cortical reaction occurs?

A

ZP2 = cleaved

makes zona pellucida impenetrable

177
Q

What happens to the 2 haploid nuclei (pronuclei) after fertilization?

A

fuse in the zygote

forms a single diploid nucleus

178
Q

What do the sperm contribute after fertilization that are not present in eggs?

A
  • centrosomes

- centrioles

179
Q

What happens to the centrosome after fertilization?

A

centrosome = duplicates

assemble mitotic spindle

180
Q

What happens in polyspermy?

A
  • extra mitotic spindles are present
  • leads to faulty segregation of chromosomes
  • aneuploidy
181
Q

What % of couples have reduced fertility?

A

10%

182
Q

When was the first child born by IVF?

A

1978

183
Q

What is ICSI?

A

intracytoplamic sperm injection

-allows men with few/non-motile sperm to father child

184
Q

What does ICSI bypass?

A
  • capacitation
  • swimming to the egg
  • acrosome reaction
  • plasma membrane fusion
185
Q

Clones have been made by transferring ________ to an unfertilized egg lacking a nucleus

A

nucleus of somatic cell

MOL BIO Exam #1- Lo (8 decks)

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