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Developmental Biology > 4: Fertilization > Flashcards

4: Fertilization Flashcards

1
Q

process in which gametes (an egg and sperm) fuse to form a zygote

A

Fertilization

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2
Q

the egg and sperm are _ , which means they each contain one set of chromosomes; upon fertilization, they will combine their genetic material to
form a zygote that is _ , having two sets of chromosomes

A

haploid
diploid

a zygote that has more than two sets of chromosomes will not be
viable; therefore, to ensure that the offspring has only two sets of
chromosomes, only one sperm must fuse with one egg

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3
Q

fertilization accomplishes two separate ends:

A

a.) sex (the combining of genes derived from two parents); and
b.) reproduction (the generation of a new organism)

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4
Q

Function of Fertilization:

A
  1. to transmit genes from parents
    to offspring
  2. to initiate in the egg cytoplasm those
    reactions that permit development to proceed
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5
Q

▪ prior to fertilization, the sperm and egg must travel toward each other, and _ can attract the sperm
▪ sperm-egg recognition occurs when proteins on the sperm cell membrane meet proteins on the _ of the egg
▪ in preparation for this meeting, the sperm cell membrane is altered significantly by _ events activated by the egg
▪ once inside the egg, the sperm activates development by causing the release of _ from within the egg
* _ these ions stimulate the enzymes needed for DNA synthesis, RNA synthesis, protein synthesis, and cell division

A

chemicals from the egg

extracellular coating

exocytotic

calcium ions (Ca2+)

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6
Q

the sperm and egg pronuclei travel toward one another, and the genetic material of the gametes combines to form the _ chromosome content carrying the genetic information for the development of a new organism

A

diploid

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7
Q

Angiosperm plants, several nuclei are involved in fertilization:
1. builds the _ that burrows to the ovary;
2. fuses with the haploid nucleus of the egg to make the _ ;
3. fuses with a diploid nucleus of a somatic cell to create the _ that nourishes the embryo

A

pollen tube
plant embryo
endosperm

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8
Q

fertilization of four major events (Barresi and Gilbert, 2020):

A
  1. Contact and recognition between sperm and egg.
  2. Regulation of sperm entry into the egg.
  3. Fusion of the genetic material of sperm and egg.
  4. Activation of egg metabolism to start development
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9
Q

this ensures
that the sperm and egg are of the same species

A

Contact and recognition between sperm and egg.

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10
Q

Only one sperm nucleus can
ultimately unite with the egg nucleus. This is usually accomplished by
allowing only one sperm to enter the egg and actively inhibiting any others
from entering

A

Regulation of sperm entry into the egg

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11
Q

Significance of Fertilization
1. Secondary oocyte to undergo 2nd maturation division to release 2nd polar body and to form haploid ovum
2. -
3. -
4. Increases metabolic acts as there are more mitochondria
5. -
6. -
7. Sex chromosome of sperm helps in sex determination
8. -

A
  1. Secondary oocyte to undergo 2nd maturation division to release 2nd polar body and to form haploid ovum
  2. restores diploidy in the zygote
  3. fertilization membrane prevents polyspermy
  4. Increases metabolic acts as there are more mitochondria
  5. Combines parents’ traits and induce variations
  6. Centrioles of sperm from the spindle to initiate the cleavage of zygote
  7. Sex chromosome of sperm helps in sex determination
  8. Copulation path sets the axis of division

COPULATION PATH is the intracytoplasmic course followed by the male pronucleus in approaching the female pronucleus during fertilization and often delineating the direction of the first cleavage furrow

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12
Q

Sequential Events of Fertilization
(Carlson, 2014)

PAABPMDCD

A
  1. Penetration of the corona radiata
  2. Attachment to the zona pellucida
  3. Acrosomal reaction and penetration of the zona pellucida
  4. Binding and fusion of sperm and egg
  5. Prevention of polyspermy
  6. Metabolic activation of the egg
  7. Decondensation of the sperm nucleus
  8. Completion of meiosis in the egg
  9. Development and fusion of male and female pronuclei
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13
Q

Penetration of the corona radiata

when the spermatozoa first encounter the ovulated egg in the _ of the uterine tube, they are confronted by the corona radiata and some remnants of the _ , which represents the outer layer of the egg complex

A

ampullary part
cumulus oophorus

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14
Q

corona radiata is a highly cellular layer with an intercellular matrix consisting
of proteins and a high concentration of carbohydrates (especially _ )

A

hyaluronic acid

hyaluronidase emanating from the sperm head plays a major role in penetration of the corona radiata, but the active swimming movements of the spermatozoa are also important

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15
Q

Attachment to the zona pellucida

  • after they have penetrated the corona radiata, spermatozoa bind tightly to the zona pellucida by means of the plasma membrane of the sperm head
  • the zona pellucida, which is 13 µm in humans, consists principally of _ – ZP1 to ZP4. _ combine to form basic units that polymerize into long filaments
A

four glycoproteins
ZP2 and ZP3

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16
Q

Attachment to the zona pellucida

o spermatozoa bind specifically to a _ , which is the terminal part of a sequence of four sugars at the end of O-linked oligosaccharides that are attached to the polypeptide core of the ZP3 molecule
o molecules on the surface of the sperm head are specific binding sites for the _ on the zona pellucida

A

sialic acid molecule

ZP3 sperm receptors

o more than 24 molecules have been proposed, but the identity of the zona-binding molecules remains unknown

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17
Q

Acrosomal reaction and penetration of the zona pellucida

on binding to the zona pellucida, mammalian spermatozoa undergo the _

A

acrosomal reaction

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18
Q

Acrosomal reaction and penetration of the zona pellucida

o in this acrosome of sperm undergoes acrosomal reaction and releases certain sperm _ which dissolve the egg envelopes locally and make the path for the penetration of sperm

A

lysins

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19
Q

Acrosomal reaction and penetration of the zona pellucida

these sperm lysins contain a lysing enzyme hyaluronidase
which dissolves the hyaluronic acid polymers in the
intercellular spaces which holds the _ of corona
radiata together

A

granulosa cells

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20
Q

Acrosomal reaction and penetration of the zona pellucida

corona penetrating enzyme (that dissolves the
_ )

A

corona radiata

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21
Q

Acrosomal reaction and penetration of the zona pellucida

_ (which dissolves the
zona pellucida; most important enzymee), then it dissolves the
zona pellucida

A

acrosin or Zona lysin

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22
Q

Acrosomal reaction and penetration of the zona pellucida

when the sperm has made its way through the zona and into the _ (the space between the egg’s plasma membrane and the zona pellucida), it can make direct contact with the plasma membrane of the egg

A

perivitelline
space

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23
Q

Binding and fusion of sperm and egg

after a brief transit period through the _ , the spermatozoon
makes contact with the egg

A

perivitelline space

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24
Q

Binding and fusion of sperm and egg

binding between the spermatozoon and egg occurs when the _ contacts the microvilli surrounding the egg

A

equatorial region
of the sperm head

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25
Q

Binding and fusion of sperm and egg

molecules on the plasma membrane of the sperm head, principally sperm proteins called _ , bind to α6 integrin and CD9 protein molecules on the surface of the egg

A

fertilins and cyritestin

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26
Q

Binding and fusion of sperm and egg

the acrosomal reaction causes a _ because, if the acrosomal reaction has not occurred, the
spermatozoon is unable to fuse with the egg

A

change in the membrane properties of the
spermatozoon

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27
Q

Binding and fusion of sperm and egg

actual fusion between spermatozoon and egg, mediated by _ on the
membrane of the oocyte, brings their plasma membranes into continuity

A

integrin

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28
Q

Binding and fusion of sperm and egg

after initial fusion, the contents of the spermatozoon (the head, the midpiece, and usually the tail) sink into the egg , whereas the sperm’s _ , which is anti-genically distinct from that of the egg, becomes incorporated into the egg’s plasma membrane and remains recognizable at
least until the start of cleavage

A

plasma membrane

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29
Q

Prevention of polyspermy

when a spermatozoon has fused with an egg, the entry of other spermatozoa
into the egg (polyspermy) must be _ , or abnormal development is
likely to result

A

prevented

two blocks to polyspermy, fast and slow, are typically present in vertebrate fertilization

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30
Q

Prevention of polyspermy

the fast block to polyspermy, which has been best studied in sea urchins, consists of a _ of the plasma membrane of the egg

A

rapid electrical depolarization

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31
Q

Prevention of polyspermy

the resting membrane potential of the egg changes from about _ within 2 to 3 seconds after fusion of the spermatozoon with the egg

A

−70 to +10 mV

this change in membrane potential prevents other spermatozoa from adhering to the egg’s plasma membrane

32
Q

Prevention of polyspermy

▪ the fast block in mammals is -, lasting only several minutes, and
may not be as heavily based on membrane depolarization as that in sea urchins
▪ this time is sufficient for the egg to mount a _
▪ however, the exact nature of the fast block in the human egg is still not well defined

A

short-lived

permanent slow block

33
Q

Prevention of polyspermy

very soon after sperm entry, successive waves of _ pass through the cytoplasm of the egg

A

Ca++

34
Q

Prevention of polyspermy

the first set of waves, spreading from the site of sperm-egg fusion, is involved in stimulating completion of the _ of the egg

A

second meiotic division

35
Q

Prevention of polyspermy

later waves of Ca++ initiate recruitment of _ in the egg and act on the _ as they pass by them

A

maternal RNAs

cortical granules

36
Q

Prevention of polyspermy

exposure to Ca++ causes the cortical granules to fuse with the _ and to release their contents (hydrolytic enzymes and polysaccharides) into the perivitelline space

A

plasma membrane

37
Q

Prevention of polyspermy

the polysaccharides released into the perivitelline space become
hydrated and swell, thus causing the zona pellucida to _ from
the surface of the egg

A

rise

38
Q

Prevention of polyspermy

the secretory products of the cortical granules diffuse into the porous zona pellucida and _ the sperm receptor molecules (ZP3 in the mouse) in
the zona

A

hydrolyze

this reaction is called zona reaction,

39
Q

Prevention of polyspermy

essentially eliminates the
ability of spermatozoa to adhere to and penetrate the zona

A

zona reaction,

40
Q

Prevention of polyspermy

the zona reaction has been observed in human eggs that have
undergone _ fertilization

A

in vitro

41
Q

Prevention of polyspermy

In addition to changes in the zona pellucida, alterations in sperm receptor molecules on the plasma membrane of the human egg cause the egg itself to become
_ to penetration by other spermatozoa

A

refractory

42
Q

the entry of the spermatozoon into the egg initiates several significant changes
within the egg (including the aforementioned fast and slow blocks to
polyspermy)

A

Metabolic activation of the egg

43
Q

Metabolic activation of the egg

in effect, the sperm introduces into the egg a soluble factor (currently thought to be a phospholipase [phospholipase _ ]), which stimulates a pathway
leading to the release of pulses of Ca++ within the cytoplasm of the egg

A

C zeta

44
Q

Metabolic activation of the egg

in addition to initiating the blocks to polyspermy, the released Ca++ stimulates a rapid intensification of the egg’s respiration and metabolism through an exchange of extracellular _ for intracellular _

A

Na+
H+

45
Q

Metabolic activation of the egg

this exchange of extracellular Na+
for intracellular H+ results in a rise in _ pH and an increase in _ metabolism

A

intracellular
oxidative

46
Q

Decondensation of the sperm nucleus

in mature spermatozoon, the nuclear chromatin is very tightly packed, in large part because of the —SS— (_ ) cross-linking that occurs among the protamine molecules complexed with the DNA during spermatogenesis

A

disulfide

47
Q

Decondensation of the sperm nucleus

shortly after the head of the sperm enters the cytoplasm of the egg, the permeability of its nuclear membrane begins to increase, thereby allowing cytoplasmic factors within the egg to affect the _ of the sperm

A

nuclear
contents

48
Q

Decondensation of the sperm nucleus

after reduction of the —SS— cross-links of the protamines to
sulfhydryl (—SH) groups by reduced glutathione in the ooplasm, the protamines are rapidly _ from the chromatin of the spermatozoon, and the chromatin begins to _ within the nucleus (now called a pronucleus) as it moves closer to the nuclear material of the egg

A

lost

spread out

49
Q

Decondensation of the sperm nucleus

it takes about _ hours for the remodeling of the sperm

A

6 to 8

50
Q

Decondensation of the sperm nucleus

▪ after a short period during which the male chromosomes are naked, histones begin to associate with the chromosomes
o during the period of pronuclear formation, the genetic material of the male pronucleus becomes _ , whereas methylation in the
female genome is _

A

demethylated
maintained

51
Q

Completion of meiosis in the egg

after penetration of the egg by the spermatozoon, the nucleus of the egg, which had been arrested in metaphase of the second meiotic division, completes the last division and releases a _ polar body into the
perivitelline space

A

second

52
Q

Completion of meiosis in the egg

the nucleus of the oocyte moves toward the _ as the result of the action of myosin molecules acting on a network of actin filaments that connect one pole
of the mitotic spindle to the _

A

cortex

53
Q

Completion of meiosis in the egg

the resulting contraction draws the entire mitotic apparatus toward the
surface of the cell; determines the _ at which both the first and second polar bodies are extruded

A

location

54
Q

Development and fusion of male and female pronuclei

a pronuclear membrane, derived largely from the _ of the egg, forms around the female chromosomal materia

A

endoplasmic reticulum (ER)

55
Q

Development and fusion of male and female pronuclei

cytoplasmic factors seem to control the growth of the female and the male _

A

pronuclei

56
Q

Development and fusion of male and female pronuclei

pronuclei appear 6 to 8 hours after sperm penetration, and they persist for about _ hours

A

10 to 12

57
Q

Development and fusion of male and female pronuclei

DNA replication occurs in the developing haploid pronuclei, and each chromosome forms _ as the pronuclei approach each other

A

two chromatids

58
Q

Development and fusion of male and female pronuclei

when the male and female pronuclei come into contact, their membranes break
down, and the chromosomes _

A

intermingle

59
Q

Development and fusion of male and female pronuclei

the maternal and paternal chromosomes quickly become organized around a mitotic spindle, derived from the _ of the sperm, in
preparation for an ordinary mitotic division

A

centrosome

60
Q

After Development and fusion of male and female pronuclei , the process of fertilization can be said to be complete, and the fertilized
egg is called a _

A

zygote

61
Q

Parthenogenesis came from Greek words

A

parthenos - virgin
genesis - birth

62
Q

natural form of asexual reproduction in which growth and development of
embryos occur without fertilization

A

Parthenogenesis

63
Q

when an ovum is activated in the absence of sperm

A

Parthenogenesis

64
Q

Parthenogenesis normal development can proceed in _ invertebrates and _ vertebrates

A

many
some

65
Q

in animals, parthenogenesis means development of an embryo from an
_

A

unfertilized egg cell

66
Q

in plants, parthenogenesis is a component process of _

A

apomixis (asexual seed
formation)

67
Q

asexual seed
formation

A

apomixis

68
Q

it is one in which the egg cell is
produced through mitosis then develops directly into an embryo
without the prior fertilization

A

apomictic parthenogenesis

69
Q

parthenogenesis naturally in some plants; some invertebrate including

A
  • nematodes,
  • water fleas,
  • some scorpions,
  • aphids,
  • some mites,
  • some bees,
  • some Phasmida and
  • parasitic wasps
70
Q

parthenogenesis occurs in few vertebrates including

A
  • some fish,
  • amphibians,
  • reptiles and
  • very rarely birds

this type of reproduction has been induced artificially in a few species
including fish and amphibians

71
Q

Parthenogenesis

normal egg cells form after meiosis and are _ , with half as many
chromosomes as their mother’s body cells

A

haploid

72
Q

haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the _ chromosome number

A

diploid

73
Q

the offspring having all of the mother’s genetic material are called _ and those having only half are called _

A

full clones
half clones

74
Q

_ clones are usually formed without meiosis

A

full

75
Q

if meiosis occurs, the offspring will get only a fraction of the mother’s
alleles since crossing over of DNA takes place during meiosis, creating
_

A

variation

76
Q

parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have _ that use the ZW sex-determination system, they have either two Z chromosomes
(male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).

A

two X chromosomes and are female in species

Developmental Biology (6 decks)

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