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Molecular Biology > Meiosis, Germ Cells and Fertilization (Lecture 6) > Flashcards

Meiosis, Germ Cells and Fertilization (Lecture 6) Flashcards

1
Q

Contains two sets of chromosomes, one from each parent

A

Diploid

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2
Q

Contains one 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

Haploid gametes fuse to form a diploid cell (zygote)

A

Fertilization

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5
Q

Divides by mitosis to become a multicellular organism

A

Zygote

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6
Q

Gametes and their precursors

A

Germline cells

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7
Q

Form the rest of the body and leave no progeny

A

Somatic cells

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8
Q

Chromosomes common to both sexes: one from each parent in each diploid nucleus

A

Autosomes

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9
Q

Meiosis creates genetic diversity in two ways

A
  • Random segregation of homologs during meiosis

- Crossing over

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10
Q

Chromosomes replicate in ____ phase

A

S

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11
Q

The two sister chromatids are bound by ____ complexes

A

cohesin

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12
Q

Homologs pair recombine and separate in

A

meiosis I

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13
Q

Is there DNA replication in Meiosis II

A

No

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14
Q

In Meiosis II is there further DNA replication

A

Yes

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15
Q

in meiosis II sister chromatids are divided to produce ___ haploid daughter cells

A

4

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16
Q

Homologs begin to pair in ______, which can last days/weeks

A

Prophase I

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17
Q

a 4 chromatid structure is called a ____-

A

bivalent

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18
Q

Stable chromosome pairing requires

A

crossing over (chiasma)

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19
Q

Homologs are joined by protein structure called _______

A

synaptonemal complex

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20
Q

Small region of homology between X and Y called _______ allows them to pair

A

pseudautosomal region

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21
Q

What are the 5 phases of prophase

A
  • Leptotene
  • Zygotene
  • Pachytene
  • Diplotene
  • Diakinesis
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22
Q

What phase of prophase do homologs begin to condense/pair

A

Leptotene

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23
Q

What phase of prophase do homologs begin to pair and synaptonemal complexes form

A

Zygotene

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24
Q

What phase of prophase is synapsis complete; crossing over occurs;

A

Pachytene

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25
Q

What phase of prophase is synaptonemal complex begins to break down; homologs begin to separate but remain attached at chiasmata

A

Diplotene

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26
Q

Reach maximum condensation; separation of homologs and transition stage into metaphase

A

Diakinesis

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27
Q

_______ filaments between homologs form synaptonemal complex

A

transverse

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28
Q

Cohesin complexes assemble on DNA during ____ phase and bind sister chromotids

A

S

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29
Q

What are the major components of axial core of each homolog and play an important role in segregating homologs in meiosis I

A

Cohesin complexes

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30
Q

arms of sister chromatids separate at ________, resolving chiasmata and allowing homologs to separate

A

Anaphase I

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31
Q

Sister chromatids separate in anaphase II when _____ cleaves chosen complexes

A

Separase

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32
Q

Homologs separate at _____

A

anaphase I

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33
Q

In meiosis Kinetochores on the 2 sister chromatids attach to microtubules coming form ___ pole

A

the same

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34
Q

The human female meiosis is arrested for years after _____ stage of prophase

A

Diplotene

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35
Q

Homologs fail to separate properly

A

Nondisjunction

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36
Q

nondisjunction errors are very common during egg development and increase with advancing _____ age

A

maternal

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37
Q

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

A

Nondisjunction

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38
Q

Cells with abnormal chromosome number

A

Aneuploid

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39
Q

example of Aneuploidy that is the most common single cause of mental retardation

A

Trisomy 21/Down syndrome

40
Q

___% of trisomy 21 individuals, the additional chromosome is maternal in origin

A

90

41
Q

Of the 90% of trisomy 21 individuals in which the additional chromosome is maternal in origin ___% occur during meiosis I and __% in meiosis II

A

70%, 30%

42
Q

Cells with normal number of chromosomes

A

Euploid

43
Q

Random distribution of maternal/paternal homologs can produce ___ different gametes

A

2^n, human example: 2^23=8.4x10^6

44
Q

The variation produced in random distribution of maternal/paternal homologs can be further increased by

A

Crossing-over (2-3 crossovers per human homolog)

45
Q

________ are found in all vertebrate embryos and give rise to gametes

A

Primordial germ cells (PGCs)

46
Q

Primordial germ cells (PGCs) migrate to _____

A

developing gonad: ovaries/testes

47
Q

Primordial germ cells proliferate through _____ and then undergo _____ to differentiate into mature haploid gametes

A

mitosis, meiosis

48
Q

Primordial germ cells proliferate through _____ and then undergo _____ to differentiate into mature haploid gametes

A

mitosis, meiosis

49
Q

Primordial germ cells proliferate through _____ and then undergo _____ to differentiate into mature haploid gametes

A

mitosis, meiosis

50
Q

In some animals, egg contains specific molecules that determine which cells become germ cells while others, including mammals, rely on ___________ signaling to dictate which become PGCs

A

Neighboring cell signaling

51
Q

In some animals, egg contains specific molecules that determine which cells become germ cells while others, including mammals, rely on ___________ signaling to dictate which become PGCs

A

Neighboring cell signaling

52
Q

In mammals, dividing egg is _____ for first few rounds of cell division; then differentiate into PGCs

A

totipotent

53
Q

When cells differentiate into PGCs somatic cell fates must be ____ by _____ and translation of certain _____ must be inhibited

A

suppressed by gene repression, RNAs

54
Q

When cells differentiate into PGCs somatic cell fates must be ____ by _____ and translation of certain _____ must be inhibited

A

suppressed by gene repression, RNAs

55
Q

Cell signaling leads to proliferation and migration of PGCs to developing gonad forming the ____ ridge

A

Genital

56
Q

PGC can be removed and cultured with signaling proteins to form cell lines

A

any cell type for the body except extra embryonic cells (pluripotent)

57
Q

_____ in genital ridge determine if gonad is ovary or testes

A

sex chromosomes (note not the sex chromosomes in the PCG itself)

58
Q

____ directs genital ridge to develop into testis. The default pathway is _____

A

Y, default pathway is female

59
Q

Sex determining region of Y

A

SRY

60
Q

____ gene is necessary and sufficient for testis development in mammals

A

Sry

61
Q

____ gene is necessary and sufficient for testis development in mammals

A

Sry

62
Q

____ gene is necessary and sufficient for testis development in mammals

A

Sry

63
Q

The SRY gene can cause sex reversal such as

A
  • XX mouse + SRY - develops as a male (sterile)

- XY male with inactivating SRY mutation -develops as a sterile female

64
Q

expression of SRY causes cells to differentiate into ____ cells, which are the support cells of the Testis

A

Sertoli

65
Q

SRY encodes _________ that regulates transcription of genes involved in Sertoli development

A

DNA binding protein

66
Q

What is the gene that is transcribed for Sertoli development

A

Sox9 (which is expressed in all vertebrates)

67
Q

Sox9 activates ____-specific genes, including _____ hormone

A

Sertoli-specific genes, including anti-Mullerian hormone

68
Q

ectopic expression of Sox9 in developing XX mouse gonads causes them to

A

develop as males (even without SRY)

69
Q

SRY in somatic cells direct differentiation into _____ instead of ____

A

Sertoli cells instead of follicle cells

70
Q

Sertoli cells secrete anti-Mullerian hormone which function include

A
  • Suppresses female development

- Causes Mullerian duct to regress

71
Q

Sertoli cells induces ____ cell differentiation in other somatic cells

A

Leydig

72
Q

What are the functions of of Leydig cells

A

Secrete testosterone (responsible for secondary sexual characteristics)

73
Q

What happens in absence of the SRY gene

A
  • Genital ridge becomes an ovary
  • PGC becomes an egg
  • Somatic cells differentiate into: follicle cells (support cells), theca cells (estrogen-producing cells)
74
Q

An activated egg can give rise to

A

completely new organism

75
Q

Egg activation is usually triggered by _____

A

fertilization

76
Q

Activation of egg in absence of sperm is called

A

Parthenogentic (this can occur in some lizards and frogs)

77
Q

Mammals cannot do Parthenogentic activation of egg due to

A

Imprinting

78
Q

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

A

Cytoplasm

79
Q

Eggs are _____ specialized

A

highly

80
Q

Eggs contain stockpiles of _____ for initial development of the embryo

A

nutrients

81
Q

____ is the nutritional reserve of an egg

A

yolk

82
Q

Yolk is rich is ____, ____ and ______

A

lipids, proteins, and polysaccharides

83
Q

________ are discrete yolk-containing structures

A

Yolk granules

84
Q

Egg coat is a ________ - rich extracellular matrix

A

Glycoprotein

85
Q

What is the function of the egg coat

A
  • protects from mechanical damage

- acts as species-specific barrier to sperm

86
Q

What is the egg coat called in non-mammalian eggs

A

Vitelline layer

87
Q

What is the egg coat called in mammals

A

Zona pellucida

88
Q

Upon egg activation, specialized secretory cells called _____ release contents, which enter egg coat and block polyspermy

A

cortical granules

89
Q

Diploid oogonia undergo ______ before entering meiosis

A

Mitotic cell divisions

90
Q

Primary oocytes are formed during

A

gestation of the human embryo

91
Q

Primary oocytes arrest at ______ of meiosis I

A

prophase I

92
Q

Secondary oocyte is arrested at

A

metaphase II

93
Q

eggs have ____ gene copies in the cell

A

extra

94
Q

egg growth occurs after _________

A

DNA replication

95
Q

eggs import yolk proteins through

A

receptor-mediated endocytosis

96
Q

eggs import yolk proteins through

A

receptor-mediated endocytosis

Molecular Biology (14 decks)

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