4: Fertilization

Question 1

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

Answer 1

Fertilization

Question 2

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

Answer 2

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

Question 3

fertilization accomplishes two separate ends:

Answer 3

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

Question 4

Function of Fertilization:

Answer 4

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

Question 5

▪ 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

Answer 5

chemicals from the egg

extracellular coating

exocytotic

calcium ions (Ca2+)

Question 6

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

Answer 6

diploid

Question 7

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

Answer 7

pollen tube
plant embryo
endosperm

Question 8

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

Answer 8

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

Question 9

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

Answer 9

Contact and recognition between sperm and egg.

Question 10

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

Answer 10

Regulation of sperm entry into the egg

Question 11

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. -

Answer 11

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

Question 12

Sequential Events of Fertilization
(Carlson, 2014)

PAABPMDCD

Answer 12

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

Question 13

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

Answer 13

ampullary part
cumulus oophorus

Question 14

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

Answer 14

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

Question 15

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

Answer 15

four glycoproteins
ZP2 and ZP3

Question 16

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

Answer 16

sialic acid molecule

ZP3 sperm receptors

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

Question 17

Acrosomal reaction and penetration of the zona pellucida

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

Answer 17

acrosomal reaction

Question 18

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

Answer 18

lysins

Question 19

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

Answer 19

granulosa cells

Question 20

Acrosomal reaction and penetration of the zona pellucida

corona penetrating enzyme (that dissolves the
_ )

Answer 20

corona radiata

Question 21

Acrosomal reaction and penetration of the zona pellucida

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

Answer 21

acrosin or Zona lysin

Question 22

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

Answer 22

perivitelline
space

Question 23

Binding and fusion of sperm and egg

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

Answer 23

perivitelline space

Question 24

Binding and fusion of sperm and egg

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

Answer 24

equatorial region
of the sperm head

Question 25

# 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

Answer 25

fertilins and cyritestin

Question 26

# 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

Answer 26

change in the membrane properties of the spermatozoon

Question 27

# 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

Answer 27

integrin

Question 28

# 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

Answer 28

plasma membrane

Question 29

# 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

Answer 29

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

Question 30

# 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

Answer 30

rapid electrical depolarization

Question 31

# 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

Answer 31

−70 to +10 mV ## Footnote this change in membrane potential prevents other spermatozoa from adhering to the egg’s plasma membrane

Question 32

# 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

Answer 32

short-lived permanent slow block

Question 33

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

Answer 33

Ca++

Question 34

# 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

Answer 34

second meiotic division

Question 35

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

Answer 35

maternal RNAs cortical granules

Question 36

# 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**

Answer 36

plasma membrane

Question 37

# 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

Answer 37

rise

Question 38

# 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

Answer 38

hydrolyze ## Footnote this reaction is called zona reaction,

Question 39

# Prevention of polyspermy essentially eliminates the ability of spermatozoa to adhere to and penetrate the zona

Answer 39

zona reaction,

Question 40

# Prevention of polyspermy the zona reaction has been observed in human eggs that have undergone _ fertilization

Answer 40

in vitro

Question 41

# 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

Answer 41

refractory

Question 42

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

Answer 42

Metabolic activation of the egg

Question 43

# 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 r**elease of pulses of Ca++** within the cytoplasm of the egg

Answer 43

C zeta

Question 44

# 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 _

Answer 44

Na+ H+

Question 45

# Metabolic activation of the egg this exchange of extracellular Na+ for intracellular H+ results in a rise in _ pH and an increase in _ metabolism

Answer 45

intracellular oxidative

Question 46

# 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

Answer 46

disulfide

Question 47

# 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

Answer 47

nuclear contents

Question 48

# 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

Answer 48

lost spread out

Question 49

# Decondensation of the sperm nucleus it takes about _ hours for the remodeling of the sperm

Answer 49

6 to 8

Question 50

# 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 _

Answer 50

demethylated maintained

Question 51

# 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

Answer 51

second

Question 52

# 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 _

Answer 52

cortex

Question 53

# 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

Answer 53

location

Question 54

# Development and fusion of male and female pronuclei a **pronuclear membrane**, derived largely from the _ of the egg, forms around the female chromosomal materia

Answer 54

endoplasmic reticulum (ER)

Question 55

# Development and fusion of male and female pronuclei cytoplasmic factors seem to control the growth of the female and the male _

Answer 55

pronuclei

Question 56

# Development and fusion of male and female pronuclei pronuclei appear 6 to 8 hours after sperm penetration, and they persist for about _ hours

Answer 56

10 to 12

Question 57

# 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

Answer 57

two chromatids

Question 58

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

Answer 58

intermingle

Question 59

# 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

Answer 59

centrosome

Question 60

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 _

Answer 60

zygote

Question 61

Parthenogenesis came from Greek words

Answer 61

parthenos - virgin genesis - birth

Question 62

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

Answer 62

Parthenogenesis

Question 63

when an ovum is activated in the absence of sperm

Answer 63

**Parthenogenesis**

Question 64

Parthenogenesis normal development can proceed in _ invertebrates and _ vertebrates

Answer 64

many some

Question 65

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

Answer 65

unfertilized egg cell

Question 66

in plants, parthenogenesis is a component process of _

Answer 66

apomixis (asexual seed formation)

Question 67

asexual seed formation

Answer 67

apomixis

Question 68

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

Answer 68

apomictic parthenogenesis

Question 69

parthenogenesis naturally in some plants; some invertebrate including

Answer 69

* nematodes, * water fleas, * some scorpions, * aphids, * some mites, * some bees, * some Phasmida and * parasitic wasps

Question 70

parthenogenesis occurs in few vertebrates including

Answer 70

* some fish, * amphibians, * reptiles and * very rarely birds ## Footnote this type of reproduction has been induced artificially in a few species including fish and amphibians

Question 71

# Parthenogenesis normal egg cells form after meiosis and are _ , with **half** as many chromosomes as their mother's body cells

Answer 71

haploid

Question 72

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

Answer 72

diploid

Question 73

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

Answer 73

full clones half clones

Question 74

_ clones are usually formed without meiosis

Answer 74

full

Question 75

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 _

Answer 75

variation

Question 76

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).

Answer 76

two X chromosomes and are female in species