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Molecular Biology > Meiosis, Germ Cells And Fertilization > Flashcards

Meiosis, Germ Cells And Fertilization Flashcards

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1
Q

How many sets of chromosomes are in a haploid cell?

A

1

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2
Q

What are gametes?

A

Specialized reproductive cells.

They are either sperm or egg generated through meiosis.

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3
Q

What is fertilization?

A

When haploid gametes fuse to form a diploid cell (zygote).

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4
Q

What is a zygote?

A

A fertilized diploid cell that divides by mitosis to become a multicellular organism.

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5
Q

What are germline cells?

A

Gametes and their precursors.

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6
Q

What are somatic cells?

A

Cells from the rest of the body (excluding germline cells) that leave no progeny.

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7
Q

What are autosomes?

A

Chromosomes common to both sexes; there is one from each parent in each diploid nucleus.

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8
Q

What are the sex chromosomes?

A

X and Y

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9
Q

How does meiosis create genetic diversity?

A

From random segregation of homologs during meiosis

From crossing over

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10
Q

What is the end product of meiosis?

A

One round of DNA synthesis that produces half the number of chromosomes.

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11
Q

When do chromosomes replicate?

A

In the S phase

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12
Q

How are two sister chromatids abound?

A

By cohesin complexes

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13
Q

When do homologs pair, recombine and separate?

A

In meiosis I.

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14
Q

What occurs during meiosis II?

A

Sister chromatids are divided to produce 4 daughter haploid cells.

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15
Q

When do homologs begin to pair?

A

During prophase I.

This can last days/weeks.

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16
Q

What is the term for a 4 chromatid structure?

A

Bivalent

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17
Q

What does the term “chiasma” refer to?

A

Crossoing over of chromosomes.

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18
Q

Homologs are joint together by what protein structure?

A

Synaptonemal complex

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19
Q

What is the pseodoautosomal region?

A

A small region of homology between X and Y. It allows the two chromosomes to pair.

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20
Q

What is the first stage of prophase?

A

Leptotene.

This is when homologs begin to condense and pair.

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21
Q

What are the five phases of prophase?

A

Leptotene

Zygotene

Pachytene

Diplotene

Diakinesis

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22
Q

What occurs during zygotene?

A

Homologs pair and synaptonemal complexes form.

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23
Q

What occurs during pachytene?

A

Crossing over

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24
Q

What occurs during diplotene?

A

Synaptonemal complex begins to break down; homologs begin to separate, but remain attached at the chiasmata.

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25
Q

What happens during diakinesis?

A

Maximum condensation is reached.

Homologs separate and transition into metaphase.

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26
Q

When do cohesin complexes assemble on DNA?

A

During S phase.

They bind sister chromatids.

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27
Q

What role do cohesin complexes play in meiosis I?

A

They play an important role in segregating homologs in meiosis I.

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28
Q

Kinetochores on two sister chromatids attach to microtubules coming from the ___ pole.

A

Kinetochores on two sister chromatids attach to microtubules coming from the SAME pole.

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29
Q

When do the arms of sister chromatids separate?

A

During anaphase I.

This resolves the chiasmata and allows homologs to separate.

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30
Q

When do sister chromatids fully separate?

A

During anaphase II.

It occurs when separase cleaves cohesin complexes.

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31
Q

You are examining an oocyte from a female donor and note that the cell is frozen in meiosis. Meiosis in oocytes is arrested for years after what stage of prophase?

A

Diplotene

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32
Q

When is meiosis I completed in human female oocytes?

A

Only at ovulation

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33
Q

When is meiosis II completed in female oocytes?

A

After fertilization.

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34
Q

What is nondisjunction?

A

When homologs fail to separate properly.

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35
Q

Trisomy 21/Down syndrome is an example of an aneuploid disorder. What does the term “aneuploid” mean?

A

An aneuploid is a cell with abnormal chromosome number.

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36
Q

What is the chromosome count in euploid cells?

A

Euploid cells have normal numbers of chromosomes.

37
Q

What are two ways in which genetic diversity can be generated?

A

Random distribution of maternal/paternal homologs

Variation increased by crossing over

38
Q

When does meiosis of male gametes begin?

A

At puberty

39
Q

What is the percentage of eggs and sperm that are aneuploid?

A

20% of eggs

3 - 4 % of sperm

40
Q

25% of all human conceptions are aneuploid. What is this mainly due to?

A

Nondisjuction in oocytes at meiosis I

41
Q

Are male or female gametes more prone to new DNA mutations?

A

Male gametes.

They are more prone as a result of undergoing more mitotic cell divisions.

42
Q

What are primordial germ cells?

A

Cells that give rise to gametes.

They migrate to developing gonads.

43
Q

How do primordial germ cells (PGCs) proliferate?

A

Through mitosis and then meiosis in order to differentiate into mature haploid gametes (sperm/egg).

44
Q

In mammals, what dictates whether a cell will become a PGC or not?

A

Neighboring cell signaling.

45
Q

In mammals, a dividing egg is totipotent for the first few rounds of cell division. What does it then differentiate into?

A

PGSs

46
Q

Are PGCs totipotent or pluripotent?

A

Pluripotent.

They can be removed and cultured with signaling proteins to form cell lines for any cell type for the body except extraembronic cells.

47
Q

What determines if a gonad is an ovary or testes?

A

Sex chromosomes in the genital ridge

48
Q

What determines the sex of an embryo?

A

Sperm.

The presence or absence of Y determines the sex of an individual.

Y directs the genital ridge to develop into testis.

49
Q

What gene is necessary for sufficient testis development in mammals?

A

Sry gene

50
Q

You do genetic testing on a mouse and determine that has XX sex chromosomes, as well as active expression of the Sry gene. What is the gender of the mouse?

A

Male (sterile)

51
Q

You conduct a genetic test on a mouse. You determine that the mouse has XY sex chromosomes and also has a mutation that inactivates the Sry gene. What is the gender of the mouse?

A

Female

52
Q

Expression of Sry causes cells to differentiate into Sertoli cells. What are Sertoli cells?

A

Testis support cells

53
Q

What are two functions of the Sry gene?

A

They cause cells to differentiate into sertoli cells.

They also encode a DNA binding protein that regulates transcription of genes involved in Sertoli development.

54
Q

What is the function of Sox9?

A

It activates Sertoli-specific genes, including anti-Mullerian hormone, which prevents development of females.

55
Q

You conduct a genetic test on a mouse and discover that the mouse has expression of Sox9, but no expression of Sry. What is the gender of the mouse?

A

Male

56
Q

Sry gene induces Leydig cell differentiation in somatic cells. What is the function of Leydig cells?

A

They secrete testosterone, which is responsible for secondary sexual characteristics.

57
Q

What occurs to a developing organism in the absence of Sry?

A

Genital ridge becomes an ovary

PGC becoms an egg

Somatic cells differentiate into
Follice cells and theca cells, which are estrogen-producing cells.

58
Q

Why can mammals not undergo parthogenic activation (activation in the absence of sperm?)

A

Due to imprinting. Mammals need two sets of chromosmes in order to develop.

59
Q

Where is the nutritional reserve found in eggs?

A

In the yolk. It is rich in lipids, proteins and polysaccharides.

60
Q

What is the function of the egg coat?

A

It protects the egg from mechanical damage and acts as a species-specific barrier to sperm (zona pellucida).

61
Q

When an egg is activated, specialized secretory cells called corticle granules release contents. What is the function of the contents?

A

They enter an egg coat and block polyspermy (more than one sperm fertilizing an egg).

62
Q

What are the stages of oogenesis?

A

PGCs migrate to the gonad

Dpiloid oogonia under mitotic and then meiotic cell divisions.

Primary oocytes arrest at prophase I

Cytoplasm divides assymetrically to produce polar body and secondary oocyte.

Secondary oocyte is arrested in metaphase II and completes meiosis only after fertilization.

63
Q

Why do eggs have such a large size?

A

They have extra gene copies in the cell.

They also have yolk proteins, accessory cells, and follicle cells.

64
Q

What is a primordial follicle?

A

The most primitive follicle. It is an oocyte surrounded by a single layer of follicle cells.

65
Q

What are follicle cells?

A

Cells that form the outer layer of an oocyte.

66
Q

What does a developing follicle look like?

A

It has multiple layers of follicle cells surrounding a growing oocyte.

67
Q

What is antrum?

A

A fluid-filled cavity found in antral follicles during puberty.

Its creation is initiated by FSH.

68
Q

What hormones trigger ovulation and the primary oocyte’s completion of meiosis I?

A

FSH and LH

69
Q

A secondary oocyte is arrested in what stage of cell division?

A

Metaphase II.

70
Q

What two hormones trigger maturation and the rupture of the secondary oocyte from the dominant atntral follicle?

A

FSH and LH

71
Q

What is contained in the acrosomal vesicle of a sperm?

A

Enzymes to help the sperm fertilize an egg.

72
Q

When does meiosis of sperm begin?

A

Puberty.

73
Q

Where does spermatogenesis occur?

A

In the seminiferous tubules.

They maintain close contact with Sertoli cells here.

74
Q

True or false: the progeny of spermatogonium do not complete cytokinesis.

A

True.

They remain connected to cytoplasm bridges in order to have access to the diploid genome for their development.

75
Q

What are the requirements for fertilization?

A

Albumin (helps extract cholesterol from the membrane, increasing ability to fuse with acrosome membrane)

Ca 2+ and H2O (they activate cAMP)

CAMP (helps to initiation capacitation-associated changes).

76
Q

What enzyme do sperm cells use to penetrate granulosa cells?

A

Hyaluronidase

77
Q

What occurs once sperm binds to the zona pellucida?

A

The sperm is altered so it can bind and fuse with the plasma membrane of an egg.

78
Q

What membrane proteins are crucial to binding?

A

ZP1 (cross links filaments)

ZP2, 3 (form long filaments)

79
Q

What does egg fusion from a sperm induce?

A

A cortical reaction in which the contents of granules are released. Meiosis resumes in egg.

80
Q

What triggers fusion of an egg and sperm?

A

Increased Ca 2+ concentration in the cytosol.

81
Q

True or false: fusion of sperm causese change in the egg plasma membrane so other sperm cannot fuse.

A

True.

This is known as inhibition of polyspermy.

82
Q

Which membrane protein is inactivated during egg activation?

A

ZP3. This prevents sperm binding to an egg or an induction of another acrosome reaction.

ZP2 is also cleaved so that the zona pellucida is impenetrable.

83
Q

After fertilization, what do sperm contribute to that are not found in the eggs?

A

Sperm contribute to centrosomes and centrioles.

84
Q

What is one consequence of polyspermy?

A

Extra mitotic spindles are present in the egg. This leads to faulty segregation of chromosomes and anueploidy.

85
Q

What is a risk involved in in vitro fertilization?

A

Multiple pregnancies.

86
Q

What is involved in ICSI?

A

Egg is injected with a single sperm.

87
Q

How have clones from many tpes of malles been made?

A

By transferring the nucleus of a somatic cell to an unfertilized egg lacking a nucleus.

88
Q

How many sets of chromosomes are in a diploid cell?

A

2

Molecular Biology (12 decks)

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