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Animal biotechnology > Gamete Biology > Flashcards

Gamete Biology Flashcards

1
Q

First and second stage of the human germline:

A
  1. Fertilisation of sperm and egg to produce a zygote
  2. Cleavage - Zygote undergoes rapid cell division without changing cell (blastomeres) sizes to form the morula
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2
Q

The morula (solid ball of cells) continuously divides to form…

A

Blastocyst

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3
Q

What are the two layers of cells which make up the blastocyst?

A

Trophectoderm and ICM

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4
Q

Next stage for blastocyst

A

Blastocyst travels down fallopian tube and implants into the uterine wall

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5
Q

Following implantation, what does the ICM do next?

A

The ICM divides into two layers called the epiblast (upper closer to amniotic cavity) and hypoblast (lower, closer to blastocyst cavity)

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6
Q

What do these two layers make up?

A

Bilaminar disc

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7
Q

Next stage?

A

Gastrulation. Bilaminar disc forms a trilaminar disc as mesoderm forms

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8
Q

Which cells are induced to form Primordial Germ Cells via signalling cascades?

A

Posterior epiblast cells

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9
Q

Which signalling molecules are responsible for this?

A

WNT/Activin/BMP

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10
Q

How many days after fertilisation do germ cells become competent?

A

10 days

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11
Q

Why is a morphogen gradient important?

A

Determines cell fate at one end compared to the other. It is difficult for cells to communicate over long distances and gradients allow communication for fate mapping.

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12
Q

This is a stochastic pattern

A
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13
Q

If this process is delayed, the potency of germ cell production decreases and the potency to form another cell type increases. What will form instead?

A

Definitive Endoderm (DE) - precursor of the gut

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14
Q

In mice, what shape is formed when the epiblast and hypoblast layers form?

A

Layers organise into a cylindrical disc rather than a flattened embryonic disc found in humans

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15
Q

Which gene is activated for the PGCs to become sex-determined?

A

SRY gene is activated in males, found on Y chromosome. SRY represses the X-linked gene, Dax1

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16
Q

What do the PGCs migrate through?

A

The gut as a group of indifferent PGCs. They reach the genital ridges (future sex organs)

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17
Q

At which time point does the erasure of epigenetic marks begin?

A

Between weeks 8 and 15

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18
Q

Are germ cells the only type of cells to remove epigenetic marks?

A

Yes

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19
Q

What happens if the maternal gene is imprinted?

A

It will have the maternal gene silenced and the paternal gene activated. Imprinting is parent-specific

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20
Q

What would happen if imprinting did not occur?

A

There would be abnormal expression and dysregulation of genes, leading to diseases and lethality

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21
Q

From week 3 to week 8, what happens to the germ cells?

A

Imprinting erasure, histone modifications

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22
Q

The first step of spermatogenesis is spermatocytogenesis, what is this?

A

PGC to a primary spermatocyte (diploid) via mitosis

23
Q

What are the next two steps?

A

Meiosis 1 and Meiosis 2. Meiosis 1 is where two haploid secondary spermatocytes are produced. Meiosis 2 is where 4 spermatids are produced.

24
Q

What is the last step?

A

Spermiogenesis. Mature sperm cells are produced from spermatids.

25
Q

During this process, what is a special feature of these cells during all the stages?

A

Bridge connections between the cells.

26
Q

What are 4 features of the post-meiotic sperm?

A
  1. Transcriptionally inactive
  2. Accumulation of mitochondria
  3. Nucleus half the size of a normal nucleus for compaction
  4. Protamines replace histones
27
Q

Why do protamines replace histones?

A

Pack the DNA to reduce transcription by preventing the polymerase from transcribing anything

28
Q

For females, what is produced from PGCs once they reach the genital ridges?

A

Primordial follicles

29
Q

Why is the egg so large?

A

It needs to accumulate so much material to support an early embryo like proteins and mRNA

30
Q

For oogenesis, what are the first two stages?

A

PGCs undergo differentiation into oogonium. These undergo mitosis and onset meiosis 1 which produce primary oocytes (2n) but arrest in prophase 1.

31
Q

The primary oocytes within the primordial follicles are arrested until puberty

A
32
Q

What happens at puberty?

A

A subset of primordial follicles are activated during each menstrual cycle and each oocyte within the follicle completes meiosis 1

33
Q

What are the two products of meiosis 1?

A

A secondary oocyte (arrested in metaphase 2 until ovulation) and a (smaller celled) first polar body

34
Q

What is the ovulation part?

A

The mature follicle undergoes ovulation and the secondary oocyte is released into the fallopian tube

35
Q

When would meiosis 2 be completed?

A

Only if fertilisation occurs and a second polar body would be released, as well as an egg (ovum)

36
Q

What are three roles of mRNAs and proteins?

A
  1. Sustain development
  2. Oocyte maturation
  3. Early development
37
Q

Storage and regulation of oocyte mRNA and proteins. Explain the 4 ways.

A
38
Q
  1. RNA polyadenylation
A

The short poly-A tails are not translated onto the mRNA and are only added when translation is needed. Prevents premature activation and controls how much RNA is utilised.

39
Q
  1. RNA masking (this is exclusive to oocytes)
A

Specific ribonucleoproteins bind to 5’ cap to prevent translational machinery from functioning

40
Q
  1. RNA localisation
A

This gives the oocyte polarity. RNA molecules are produced and transported to a specifc region of the oocyte. They make up the germplasm (only in lower vertebrates, NOT mammals) which is at one pole of the oocyte too. This is essential for the establishment of the germline.

41
Q
  1. Protein phosphorylation
A

Control of kinases which maintain the cell cycle, controlling phosphorylation which activates or deactivates processes.

42
Q

What response is triggered when the sperm joins the plasma membrane during fertilisation?

A

ER releases calcium which triggers exocytosis of cortical granules

43
Q

What effect does this have?

A

This changes the plasma membrane polarity so that no other sperm can bind

44
Q

What also happens at the same time and why?

A

Activation of the proteasome which can degrade cyclin B which was causing the arrest of the oocyte in metaphase 2. (zygote can now divide)

45
Q

What happens to the sperm DNA?

A

It is unwrapped and protamines are removed. They are replaced by maternal histones (from oocytes)

46
Q

Why?

A

The sperm DNA is used to build the nucleus

47
Q

What is the simple process of IVF?

A

Select genetically valuable stem cells from animal of interest and differentiate into gametes. IVF with gametes to produce embryo. Many cycles over many months (rapid method) for rapid incorporation of traits.

48
Q

What are the four steps for IVF?

A
  1. Oocyte maturation
  2. Sperm capacitization
  3. Fertilisation
  4. In vitro culture
49
Q

What is the procedure through which oocytes of genetic value are collected in cattle?

A

Ovum Pick Up (OPU)

50
Q

What is nuclear transfer?

A

The reconstruction of an embryo by the transfer of genetic material from a donor cell to a recipient egg where the genetic material has been removed

51
Q

What are three benefits of using somatic donor cells for nuclear transfer?

A
  1. Unlimited source of donor cells
  2. Can produce many clones from a somatic cell
  3. Can genetically modify the somatic cells for when they have their genetic material transferred
52
Q

There have been fetal abnormalities, what is the main defect that causes this?

A

All related to the formation of the placenta

53
Q

Which two species is ICSI (Intracytoplasmic Sperm Injection) successful (40%) in for treating infertility?

A

Mice and humans. Not efficient in cattle, sheep, or pigs

Animal biotechnology (8 decks)

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