L30 - Female reproductive cycle

Question 1

Meiosis overview

Answer 1

One DNA replication with two divisions

Meiosis I: separation of homologous chromosomes

Meiosis II: separation of sister chromatids

Question 2

Meiosis Stages breakdown

Answer 2

1) Prophase I

• Preleptotene (DNA synthesis)
• Leptotene (size increases; chromosomes visible)
• Zygotene (pairing of chromosome at some points)
• Pachytene (pairing along the entire chromosomes, shortening and thickening of chromosome; crossing over)
• Diplotene (formation of chiasmata - site of crossing over)
• Dictyotene (prolonged resting phase in oogenesis)
• Diakinesis (shortening and thickening of chromosome)

2) Metaphase I (disappearance of nuclear membrane; chromosomes alignment at equator, attachement to spindel fibre)

3) Anaphase I (separation of chromosomes)

4) Telophase I (Formation of nuclear membrane)

5) Prophase II (spindle fiber formation

6) Metaphase II (disappearance of nuclear membrane; chromosomes alignment at equator, attachement to spindel fibre)

7) Anaphase II (separation of chromatids)

8) Telophase II (Formation of nuclear membrane)

Question 3

Oogenesis flow chart

Answer 3

1) Primordial Germ Cells (2n)

[mitosis, migration to genital ridge]

2) Oogonia (2n)

[mitosis, DNA synthesis, meiosis I (prophase I)]

3) Primary oocyte (4n, arrested at prophase I, 8-9 weeks)

[After birth: Growth of oocyte and follicle]

3) Primary oocyte (4n, larger)

[Puberty: Follicular maturation, complete meiosis I, starts meiosis II (metaphase II)]

4) Secondary oocyte (2n, arrested at metaphase II)

[ovulation]

4) Secondary oocyte (2n)

[fertilization]

5) Ootid/Pronucleate egg (n)

Question 4

Characteristics of meiosis in oogenesis

Answer 4

– start before birth/ends after fertilization (ceiling on number of germ cells)

– arrest at prophase I and metaphase II

– Unequal cell division (polar bodies)

Question 5

Ovary germ cell number with age

Answer 5

Decreases with age; cannot replenish

* Steep increase before birth due to mitosis

* Steep decrease after peak due to meiosis

Question 6

Brief overview of follicogenesis

Answer 6

• primordial follicle
• > developing follicle
• > mature follicle
• > ovulated follicle
• > corpus luteum

Question 7

Classification of Follicle

Answer 7

1) Primordial (<50 mew m; Primary oocyte, single layer of flattened granulosa cells)
2) Primary (50-100 mew m; primary oocyte, Increase size of oocyte, zona pellucida, proliferation of follicular cells)
3) Secondary (100-1000 mew m; primary oocyte, formation of antrum & cumulus)
4) Tertiary (>1000 mew m; secondary oocyte, resumption of meiosis, increase size of antrum, stigma)

Question 8

Follicle structure

Answer 8

(from internal to external)

1) oocyte
2) microvilli
3) zona pellucida
4) basal lamina
5) granulosa
6) theca

* antrum - fluid-filled cavity adjacent to oocyte

* corona radiata, cumulus oophorus - at granulosa

Question 9

Phases of follicle development

Answer 9

1) Preantral phase
2) Antral phase
3) Preovulatory phase
4) Ovulatory phase
5) Luteal phase