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Reproductive Biology > Fertilization and Meiosis (Lec 4) > Flashcards

Fertilization and Meiosis (Lec 4) Flashcards

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1
Q

Gametes

A

Male: Spermatozoa produced in testes
Female: Ovum produved in ovaries

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2
Q

Preparation for Meiosis

A

Replication of DNA in ‘S phase’ of Interphase

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3
Q

Meiosis

A

Eukaryotic cell division that produces Haploid gametes and reshuffles genetic material. Introduces variation by:

  • Crossing Over
  • Independant Assortment
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4
Q

Meiosis I: Reductional Division

A

Prophase I: condensed homologous pairs undergo synapsis, nuclear membrane dissolves, spindles form

Metaphase I: chromosomes align at equator, spindle fibres attach to centromeres

Anaphase I: chromosomes split, drawn to opposite poles

Telophase I: spindle disappears, nuclear membrane forms

Cytokinesis: cytoplasm separates, 2 separate cells formed

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5
Q

Meiosis II: Equational Division

A

Prophase II: nuclear membrane dissolves, spindles form

Metaphase II: chromosomes align at the equator

Anaphase II: sister chromatids separate and are drawn to opposite poles by spindle fibres

Telophase II: spindle disappears, nuclear membrane forms

Cytokinesis: cytoplasm separates, 2 separate cells formed

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6
Q

Introduction of Variation: Crossing Over

A

Occurs during Prophase I only. Crossing over of genetic information between 2 non-sister chromatids, several chiasmata depending on chromosome length

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7
Q

Introduction of Variation: Independent Assortment

A

Distribution into daughter cells is random.

  • Anaphase I: either homologous chromosome drawn to the poles
  • Anaphase II: either sister chromatid drawn to the poles
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8
Q

Oogenesis

A

Primary oocytes rest in Prophase of Meiosis I, after Mencarche FSH stimulates follicles to grow every cycle. Result: 2 cells (Secondary Oocyte and 1st Polar Body)

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9
Q

Spermatogenesis

A

Spermatogonium -> Primary Spermatocyte

  • > 1st Meiotic Divison = Secondary Spermatocyte
  • > 2nd Meiotic Division = Spermatids
  • > Maturation (Sertoli Cells) = Sperm
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10
Q

Aneuploidy

A

Abnormal number of chromosomes in a cell

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11
Q

Numerical Aberrations of Sex Chromosomes

- Monosomy X (Turner Syndrome)

A

Karyotype: 45, X (Genetically female)

Sterility, short stature, webbed neck

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12
Q

Numerical Aberrations of Sex Chromosomes

- Trisomy X (Triple X)

A

Karyotype: 47, XXX (Genetically female)

Healthy and fertile, phenotypically normal

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13
Q

Numerical Aberrations of Sex Chromosomes

- Klinefelter Syndrome

A

Karyotype: 47, XXY (Genetically male)

Feminine body characteristics, usually tall (long limbs), small testes and sterile

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14
Q

Numerical Aberrations of Sex Chromosomes

- Double YY

A

Karyotype: 47, XYY (Genetically male)

Normal fertility and sexual development, often taller than average

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15
Q

Numerical Aberrations of Autosomes

- Patau Syndrome (Trisomy 13)

A

Karyotype: 47, +13

Brain, eye, circulatory defects, cleft palate, rarely live more than a few months

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16
Q

Numerical Aberrations of Autosomes

- Edward’s Syndrome (Trisomy 18)

A

Karyotype: 47, +18

Almost every organ system affected, rarely live longer than a few months

17
Q

Numerical Aberrations of Autosomes

- Down Syndrome (Trisomy 21)

A

Karyotype: 47, +21

Epicanthic folds, short stature, IQ mildly impaired, congenital heart abnormalities

18
Q

Polyploidy

A

More than 2 sets of comlpete chromosomes (e.g. Tetraploids)

19
Q

Fertilization

A

Egg must be fertilized within 12-24 hours

  • Takes ovum 72 hours to reach uterus
  • Sperm viable for up to 6 days
20
Q

Sperm Activation: Capacitation

A

Chemical changes of sperm after entering female reproductive tract
− Sperm head becomes penetrable to Ca2+ ions
− Hypermotility of sperm

21
Q

Sperm Activation: Acrosome Reaction

A

Acrosome reaction induced by Ca2+, progesterone + other factors
− Acrosome vesicle fuses with the Zona Pellucida and releases digestive enzymes which soften the glycoprotein matrix of the Zona Pellucida → sperm can penetrate

22
Q

Fertilization Process

A

(1) Sperm penetration of Cumulus cells
(2) Attachment to Zona Pellucida
(3) Exocytosis of acrosomal contents (enzymes digest the Zona Pellucida)
(4) Penetration of Zona Pellucida
(5) Entry into Perivitelline Space
(6) Membrane fusion of sperm and ovum → sperm nucleus enters cytoplasm
(7) Cortical reaction: enzymes released
(8) Block to polyspermy

23
Q

Preventing Polyspermy

A

Cortical Reaction:
− Triggered by Ca2+ release by the release of cortical granules from ovum
− Exocytosis of cortical granules from ovum modify extracellular matrix (Zona Pellucida) by serine proteases

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