Gametogenesis and IVF

Question 1

Where are chromosomes located in a cell?

Answer 1

In the nucleus

Question 2

How many pairs of chromosomes are present in a human cell?

Answer 2

23 pairs: 22 pairs of autosomes + 1 pair of sex chromosomes.

Question 3

When does DNA replication occur during the cell cycle?

Answer 3

In the S phase (synthetic phase) of interphase.

Question 4

How many chromosomes are present in a diploid human cell?

Answer 4

46 chromosomes (2n) — 23 from mother, 23 from father.

Question 5

What is the difference between autosomes and sex chromosomes?

Answer 5

Autosomes: Pairs 1–22

Sex chromosomes:

XX = Female

XY = Male

Question 6

What are the structural parts of a chromosome?

Answer 6

Short arm (p arm)

Long arm (q arm)

Centromere

Two chromatids after DNA replication

Question 7

What’s the difference between a single and a duplicated chromosome?

Answer 7

Single chromosome: Before DNA replication

Duplicated chromosome: After DNA replication, consists of 2 sister chromatids joined at the centromere

Question 8

What does the centromere connect in a chromosome?

Answer 8

The short arm (p arm) and the long arm (q arm).

Question 9

What do the symbols “n” and “N” refer to in genetics?

Answer 9

n = Number of chromosomes

N = Amount of DNA

Question 10

What is the genetic status of a cell after DNA replication?

Answer 10

n, 2N — chromosome number unchanged, DNA content doubled.

Question 11

What are homologous chromosomes?

Answer 11

Chromosome pairs (1 maternal + 1 paternal) with the same loci (e.g., for eye color, hair color) but possibly different alleles.

Question 12

What is a locus on a chromosome?

Answer 12

A fixed position on a chromosome where a specific gene is located (e.g., eye color locus, hair color locus).

Question 13

What is the chromosome number in a primary spermatocyte/oocyte?

Answer 13

Diploid (2n) — 46 chromosomes.

Question 14

What happens in the first meiotic division?

Answer 14

Chromosome number is halved

Produces 2 haploid (n) cells (23 chromosomes each)

Question 15

What happens in the second meiotic division?

Answer 15

Sister chromatids separate

Produces 4 haploid gametes (each with 23 chromosomes)

Question 16

What are the chromosome numbers of sperm, oocyte, and zygote?

Answer 16

Sperm: 23 (haploid)

Oocyte: 23 (haploid)

Zygote: 46 (diploid)

Question 17

What is the chromosomal composition of the zygote?

Answer 17

46 chromosomes — 23 maternal + 23 paternal

Question 18

What does the zygote divide to form?

Answer 18

The blastocyst, which contains the inner cell mass (ICM).

Question 19

What forms from the inner cell mass (ICM) of the blastocyst?

Answer 19

The epiblast, which gives rise to primordial germ cells (PGCs).

Question 20

What is the first sex cell of the body?

Answer 20

Primordial Germ Cell (PGC)

Question 21

What cells arise from PGCs?

Answer 21

Gonocytes

Gametogonia → These form primary & secondary gametocytes.

Question 22

What is the pathway of PGC migration?

Answer 22

Origin: Epiblast (2n, 2N)

Migration through: Ectoderm → Mesoderm → Genital Ridge

Question 23

What happens if PGCs fail to reach the genital ridge?

Answer 23

They may lodge in ectoderm, endoderm, or mesoderm → Germ cell tumors.

Question 24

What types of cell division occur during gametogenesis?

Answer 24

Mitosis (equational division)

Meiosis (two-stage process)

Question 25

Why is meiosis I called a reductional division?

Answer 25

Because it halves the number of chromosomes (2n → n)

Question 26

What separates during meiosis I?

Answer 26

Homologous chromosomes

Question 27

What separates during meiosis II?

Answer 27

Sister chromatids

Question 28

Why can germ cell tumors contain all three germ layers?

Answer 28

Because primordial germ cells (PGCs) are pluripotent.

Question 29

Name two examples of germ cell tumors.

Answer 29

Oropharyngeal teratoma Sacrococcygeal teratoma

Question 30

What is the sequence from PGC to gamete in males?

Answer 30

PGC → Gametogonium → Primary spermatocyte → Meiosis

Question 31

What is the sequence from PGC to gamete in females?

Answer 31

PGC → Gametogonium → Primary oocyte (enters meiosis I in utero)

Question 32

Is there a cell division between gametogonium and primary oocyte?

Answer 32

No, the gametogonium just enlarges to become the primary oocyte.

Question 33

When does Meiosis I begin in males and females?

Answer 33

Females: In utero (fetal life) Males: Only after puberty

Question 34

What happens to PGCs in males before puberty?

Answer 34

They remain dormant.

Question 35

What happens during Prophase of mitosis?

Answer 35

Chromosomes condense Nuclear envelope breaks down Spindle fibers grow from centrioles Centrioles migrate to opposite poles

Question 36

What happens during Metaphase of mitosis?

Answer 36

Chromosomes align at the equator (metaphase plate).

Question 37

What happens during Anaphase of mitosis?

Answer 37

Sister chromatids separate and move to opposite poles.

Question 38

What happens during Telophase of mitosis?

Answer 38

Chromatids arrive at poles Two daughter nuclei form

Question 39

What happens to chromosomes during Metaphase?

Answer 39

Chromosomes align at the midline (metaphase plate) Some spindle fibers attach to kinetochores Aster fibers anchor to the plasma membrane

Question 40

What are kinetochores?

Answer 40

Protein structures on chromosomes where spindle fibers attach during cell division.

Question 41

What happens during Anaphase?

Answer 41

Centromeres divide Spindle fibers pull sister chromatids to opposite poles Each future daughter cell gets an identical set of genes

Question 42

What key event marks the end of Anaphase?

Answer 42

Each pole has a complete and identical set of chromosomes.

Question 43

What happens during Telophase?

Answer 43

Chromosomes gather at each pole Chromatin decondenses New nuclear envelopes form at each pole Nucleoli reappear in each new nucleus

Question 44

What is the outcome at the end of mitosis?

Answer 44

Two daughter cells Each has 2n chromosomes and 2N DNA, identical to the parent cell.

Question 45

Where does mitosis occur and how many divisions does it involve?

Answer 45

Occurs in somatic cells Completes in one sequence (1 division)

Question 46

Where does meiosis occur and how many divisions does it involve?

Answer 46

Occurs in germ cells Has two divisions: Meiosis I and Meiosis II

Question 47

Does crossing over occur in mitosis?

Answer 47

No — no exchange of genetic material.

Question 48

Does crossing over occur in meiosis?

Answer 48

Yes — chromatids exchange genetic material during Prophase I.

Question 49

Chromosome number in daughter cells after mitosis?

Answer 49

Same as parent (diploid → diploid)

Question 50

Chromosome number in daughter cells after meiosis?

Answer 50

Half the number of parent cell (diploid → haploid)

Question 51

Are the daughter cells from mitosis identical?

Answer 51

Yes — both to each other and to parent cell.

Question 52

Are the daughter cells from meiosis identical?

Answer 52

No — they differ from each other and the parent cell due to crossing over.

Question 53

What kind of division is mitosis?

Answer 53

Equational division

Question 54

What kind of division is meiosis I?

Answer 54

Reductional division (2n → n)

Question 55

What are the stages of Prophase I in meiosis?

Answer 55

1. Leptotene 2. Zygotene 3. Pachytene 4. Diplotene 5. (Diakinesis – not mentioned but part of standard list)

Question 56

What happens during Leptotene?

Answer 56

Chromosomes begin condensation.

Question 57

What happens during Zygotene?

Answer 57

Homologous chromosomes pair to form bivalents.

Question 58

What happens during Pachytene?

Answer 58

Bivalents appear as tetrads and crossing over occurs.

Question 59

What is a chiasma?

Answer 59

The point where chromatids cross over during Pachytene.

Question 60

What happens during Diplotene?

Answer 60

Separation of homologous chromosomes begins.

Question 61

What are the four chromatids involved in a bivalent?

Answer 61

2 paternal sister chromatids 2 maternal sister chromatids

Question 62

What forms during Zygotene stage of Prophase I?

Answer 62

Synaptonemal complex assembles between homologous chromosomes → forming bivalents

Question 63

What happens during Pachytene?

Answer 63

Crossing over occurs Chromatids become a tetrad

Question 64

What marks the Diplotene stage?

Answer 64

Separation of maternal & paternal chromosomes Disassembly of synaptonemal complex

Question 65

How many chromosomes does the primary oocyte/spermatocyte have after DNA replication?

Answer 65

46 double-structured chromosomes

Question 66

What is the result of the first maturation division in gametogenesis?

Answer 66

Secondary spermatocytes / secondary oocyte Each has 23 double-structured chromosomes

Question 67

What happens during the second maturation division?

Answer 67

Secondary spermatocytes → 4 spermatids (in males) Secondary oocyte → 1 mature oocyte + 2 polar bodies (in females)

Question 68

Chromosome number in mature oocyte and spermatid?

Answer 68

23 single chromosomes Either 22 + X or 22 + Y

Question 69

When and where is the primary oocyte arrested?

Answer 69

In Prophase I (Dictyotene stage) From fetal life until puberty

Question 70

What breaks the primary oocyte arrest in Prophase I?

Answer 70

LH surge at puberty → leads to ovulation

Question 71

After ovulation, what is the next arrest point?

Answer 71

Secondary oocyte gets arrested in Metaphase II

Question 72

What’s the mnemonic to remember the Metaphase II arrest?

Answer 72

M2F = Metaphase II arrest until Fertilization

Question 73

What happens if fertilization does NOT occur?

Answer 73

Secondary oocyte degenerates Leads to menstruation

Question 74

What happens if fertilization DOES occur?

Answer 74

Meiosis II resumes Produces: Mature oocyte 2nd polar body

Question 75

What causes the arrest of primary oocytes in Prophase I until puberty?

Answer 75

OMI (Oocyte Maturation Inhibitor) → increases cAMP, preventing progression

Question 76

How does LH surge allow resumption of meiosis in oocytes?

Answer 76

It reduces cAMP levels → breaking OMI-induced arrest → oocyte progresses to Meiosis I

Question 77

Where are PGCs located at birth in males and females?

Answer 77

Ovary (♀): Primary oocytes arrested in Prophase I Testis (♂): PGCs dormant until puberty

Question 78

How long does spermatogenesis take?

Answer 78

Approximately 74 days

Question 79

How long does oogenesis take?

Answer 79

Can take years, from fetal life until fertilization

Question 80

What is the chromosomal status of the oogonium (before S phase)?

Answer 80

2n, 2N

Question 81

What is the chromosomal status of the primary oocyte (after S phase)?

Answer 81

2n, 4N

Question 82

What is the chromosomal status of the secondary oocyte after Meiosis I?

Answer 82

n, 2N

Question 83

What is the chromosomal status of the mature oocyte (ovum) after Meiosis II?

Answer 83

n,N

Question 84

What is the chromosomal status of the zygote?

Answer 84

2n, 2N

Question 85

When does the LH surge occur before ovulation?

Answer 85

36 hours before ovulation

Question 86

When is the LH peak reached before ovulation?

Answer 86

About 12 hours before ovulation

Question 87

When is the 1st polar body released in the menstrual cycle?

Answer 87

At LH peak (~12 hours before ovulation)

Question 88

What is the most fertile period in a menstrual cycle?

Answer 88

3 days around Day 14 (ovulation)

Question 89

What event defines Day 1 of the menstrual cycle?

Answer 89

Menstruation begins

Question 90

What is the average duration of a normal menstrual cycle?

Answer 90

28 days

Question 91

On which day does ovulation typically occur?

Answer 91

Day 14

Question 92

When does the LH surge occur in relation to ovulation?

Answer 92

36 hours before ovulation

Question 93

When does LH peak occur before ovulation?

Answer 93

12 hours before ovulation

Question 94

What is released during the LH peak?

Answer 94

1st polar body

Question 95

When is the 2nd polar body released?

Answer 95

After fertilization

Question 96

How long is sperm viable in the female genital tract after ejaculation?

Answer 96

48 hours (2 days)

Question 97

When is the most fertile period in the menstrual cycle?

Answer 97

3 days around ovulation (usually Day 13–15)

Question 98

What condition requires IVF due to natural fertilization failure?

Answer 98

Bilateral tubal blockage

Question 99

Which drug is used to hyperstimulate ovaries in IVF?

Answer 99

Clomiphene citrate

Question 100

Which follicles are aspirated during IVF?

Answer 100

Graafian follicles (just before ovulation)

Question 101

Which oocytes are collected during IVF?

Answer 101

Secondary oocytes

Question 102

At what stage is the embryo usually implanted in the uterus in IVF?

Answer 102

Morula (8-cell stage) or sometimes 32-cell stage

Question 103

Which cell undergoes fertilization?

Answer 103

Secondary oocyte in metaphase arrest

Question 104

After entering Meiosis I, primary oocyte remains arrested in which stage?

Answer 104

Diplotene

Question 105

At what stage does the conceptus reach the uterine cavity?

Answer 105

16-cell stage