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Cell and Developmental biology > Gametogenesis to mid-blastula transition > Flashcards

Gametogenesis to mid-blastula transition Flashcards

1
Q

steps of fertilisation

A

fusion of gametes, creation of first zygotic cell, restores diploid chromosomes, initiates cell cycle

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2
Q

steps of gametogenesis

A

germ cell vs somatic cell, halving of genetic content, homologous recombination

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3
Q

what is the outcome of germ cell development

A

a male gamete or female gamete

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4
Q

what to germ cells give rise to

A

all cells in an organism - only cells to undergo meiosis

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5
Q

why is there a reduction division in formation of the germ line

A

if there was no reduction then the no of chromosomes in somatic cells would double with each generation

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6
Q

what are the precursor germ cells

A

primordial germ cells - formed in locations that seem to protect them from inductive signals that determine the fate of somatic cells and shut down the somatic development programme

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7
Q

in drosophila how is movement of transposons prevented

A

by an rna silencing pathway

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8
Q

what is a germplasm

A

a special cytoplasm that specifies primordial germ cells

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9
Q

what is an example of a germplasm? (drosophila)

A

primordial germ cells (pole cells) become distinct at the posterior pole of the egg 90 mins after fertilisation, the cytoplasm at the posterior end is the pole plasm which is distinguished by large organelles
polar granules contain proteins and rnas

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10
Q

what happens when the posterior end of a drosophila egg is irridated by UV light

A

it destroys pole plasm activity so no germ cells develop, somatic cells in this region still develop

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11
Q

what happens if the pole plasm from an egg is transferred to another embryos anterior pole?

A

nuclei in the area are specified as germ cell nuclei - if this is then transplanted to a 3rd embryos posterior end the cells develop as fucntional germ cells

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12
Q

what does the oskar gene play a role in?

A

organisation and assembly of the pole plasm, only gene involved in pole plasm formation that has mRNA localised at the posterior pole
the signal for this localisation is in the 3’ untranslated region of mRNA

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13
Q

what protein is required for oskars localisation

A

staufen protein, it links mRNA to the microtubule system polarised along the antero-posterior axis

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14
Q

what happens if oskars genes for 3’ localisation are replaced by bicoid 3’ localisation?

A

oskar mRNA will be localised at the anteriors of the egg - this is manipulation of DNA

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15
Q

when is germline lineage set up in the nematode?

A

at the end of the 4th cleavage division with all germ cells derived from the p4 blastomere - p4 cells are derived from 3 stem cell like divisions of p1 cells

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16
Q

what happens at each division of the nematode

A

1 daughter produces somatic cells and the other divides again to produce a somatic cell progenitor (P cell)

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17
Q

where does the nematode egg produce P granules and how are they distributed

A

produces p granules in its cytoplasm then asymmetrically distributed before the first cleavage division - then subsequently confined to the p cell lineage

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18
Q

what are p granules suggested to have a role in

A

due to their association with germ cell formation they may have a role in germ cell specification

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19
Q

what is pg 1-1 gene needed for?

A

germ cell development it is a p granule component

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20
Q

in the fly and nematode what is transcription repression needed for?

A

specification of germ cell fate

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21
Q

when are p granules localised

A

after fertilisation - to the posterior end of the cell

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22
Q

when is diploid chromosome reinstated

A

after fertilisation

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23
Q

when does meiosis occur

A

when the germ cells reach the gonad

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24
Q

when are chromosomes replicated in meiosis

A

1st division not 2nd

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25
Q

what happens when cell divisions are unequal

A

a small structure called a polar body is formed

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26
Q

what happens during prophase of 1st division

A

replicated homologous pair undergo division and dna sequences are exchanged

27
Q

what does meiosis result in

A

gametes with variations of alleles compared to the parents which is the main source of genetic variation

28
Q

draw out meiosis

A

see notes

29
Q

in oogenesis what are the diploid germline cells called

A

oogonia

30
Q

after entry into meiosis what are cells called in oogenesis?

A

primary oocytes

31
Q

how are oocytes found in the ovary

A

enclosed in a sheath of somatic ovarian cells called the follicle

32
Q

how are mammalian primary oocytes arrested in 1st prophase

A

dependant on cAMP levels within the oocyte generated from signalling of g protein coupled receptors

33
Q

when is the first mitotic division completed for oocytes

when does the second division occur

A

after ovulation of the adult, the second meiotic division occurs after fertilisation

34
Q

in humans when do most oocytes degenerate

A

during puberty

35
Q

when does meiosis occur in mammals

A

during ovulation, egg is released and the oocyte undergoes and completes its 1st meiotic division to produce a polar body it then proceeds until metaphase of the second meiotic division

36
Q

what are polar bodies

A

small cells formed by meiosis during the development of an oocyte into an egg

37
Q

what is a major error in human oocyte production

A

extra chromosome 21 leading to downs syndrome

most embryos with too few or too many chromosomes are non viable

38
Q

what happens to diploid germ cells that give rise to sperm

A

they do not undergo meiosis at the embryo but they become arrested at an early stage of mitotic ell cycle in embryonic testis - they assume mitotic proliferation after birth

39
Q

in sexually mature animals what to spermatogonial stem cells give rise to

A

differentiating spermatocytes which undergo meiosis to form 4 haploid spermatids that mature into sperm

40
Q

what is the difference between female egg production and male sperm production?

A

females do not produce more eggs throughout their lives, males produce sperm throughout lives

41
Q

what is different about drosophila sperm and egg production to mammals

A

they have a continuous production of both eggs and sperm in females and males respectively

42
Q

what is genomic imprinting and what evidence is there of it

A

where certain genes are switched off in either the sperm or egg during development and remain silenced in the genome of the early embryo
evidence in mammals - demonstration of maternal and paternal genomes making different contributions to embryonic development

43
Q

how can mouse genomic imprinting be manipulated

A

manipulated to have 2 paternal or 2 maternal genomes and can be re-implanted at a later stage - both embryos would be diploid but development is abnormal

44
Q

what happens to mice with 2 paternal genomes

A

they dont proceed beyond several somites

45
Q

what happens to mice with 2 maternal genomes

A

they have relatively well developed embryos but placenta and yolk sac are not well developed

46
Q

why does imprinting need to be irreversible

A

so that the next generation can become male or female

47
Q

when is inherited imprinting erased and re-established

A

inherited imprinting erased during early germ cell development and later established during germ cell differentiation

48
Q

what happens to imprinting when mammals are cloned

A

donor nuclei will not have gone through normal reprogramming and imprinting so abnormalities are shown

49
Q

what are spermatozoon designed to do

A

activate egg cells and deliver their nucleus into the egg cytoplasm

50
Q

what is the anterior end of the spermatozoon specialised for

A

penetration of the physical barriers of the egg

51
Q

what are the cumulus cells of the egg

A

a sticky layer of hyaluronic acid embedded in somatic follicle cells

52
Q

how do sperm penetrate the cumulus layer of the egg

A

hylauronidase on its surface allows penetration

53
Q

what is the zona pellucida

A

a layer of fibrous glycoproteins secreted by the oocyte, it is a physical barrier

54
Q

how do sperm penetrate the zona pellucida

A

they secrete enzymes from the acrosome released by exocytosis

55
Q

what are the 3 regions of the spermatozoon and what do they each contain

A

head - acrosome, nucleus (contains DNA)
mid piece - centrosome and mitochondria
tail - flagellum
all surrounded by the plasma membrane

56
Q

how are other sperm blocked from entering an egg post fertilisation

A

resting membrane potential rapidly increased then slowly returns to normal - this depolarisation provides block to polyspermy and ensures only one sperm reaches the egg cell membrane

57
Q

how is the vitelline membrane lifted after fertilisation

A

cortical granules release their content between the egg plasma membrane and the vitelline membrane

58
Q

how is the hardened fertilisation membrane produced

and what happens to the remaining cortical granule

A

follow the lifting of the vitelline membrane, cortical granules then cross link the molecules in the vitelline membrane to produce the hardened membrane
the remaining cortical granule material forms the hyaline layer

59
Q

how does the calcium wave at fertilisation occur and what does it trigger

A

it is triggered by release of stores at sperm entry (from sperm enzymatic activity of phospholipase C) and triggers the completion of meiosis in the fertilised egg

60
Q

when do maternal effect genes have effects in drosophila

A

at the start of the mid-blastula transition

61
Q

when are nurse cells in drosophila development produced

A

a germline cell undergoes an asymmetrical division to produce another stem cell and a cystoblast
the cystoblast undergoes 4 mitotic divisions to give 16 cells with cytoplasmic bridges between them this is a germline cyst
one of these 16 cells becomes an oocyte and the other 15 become nurse cells

62
Q

what do nurse cells do

A

produce protein and RNA that are exported into the oocyte through the cytoplasmic bridges

63
Q

how is the egg chamber formed

A

soamtic ovarian cells forma sheath of follicle cells around the nurse cells and oocyte = egg chamber

64
Q

what do follicle cells play a key role in

A

forming eggs axis

Cell and Developmental biology (13 decks)

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