EMBRYOL Chapter 4 - Fertilization and Cleavage

a process not a single event; begins with sperm cell contact with egg, ends with the intermingling of maternal and paternal chromosomes at the metaphase plate prior to the first cleavage division

a more efficient mechanism of fertilization; characteristic of mammals

initial membrane contact between sperm and egg

entry of sperm into the egg

prevention of polyspermy

metabolic activation of the egg

completion of meiosis by the egg

formation and fusion of male/female pronuclei -leading to the first cleavage division

entry of more than one sperm into the egg cell

at cellular level, they are covered by a noncellular jelly coat, and the eggs complete their second meiotic division before the entry of spermatozoon

eggs are surrounded by a cellular layer (not a jelly coat) and must complete the second meiotic devisionjelly coat,

Female extrudes egg

Male floods area with spermatozoa

thick outer investment; is composed of a mixture of small peptides, glycoproteins, and a polysaccharide containing fucose sulfate units.

Direct contact with jelly coat increases motility and stimulates the ____

a decapeptide (10 amino acids), in one species of sea urchin, that is responsible, at least in part, for the increased motility and activated respiration that occur when the sperm contacts jelly coat

an increase in permeability of the plasma membrane of the sperm to Ca++ and an increased concentration of intracellular Ca++ and a subsequent exchange of inside the sperm head for extracellular Na+.

stimulated by an exchange of extracellular Ca++ with intracellular K+, and if the intracellular pH is higher than 7.2, it begins with a localized fusion of the outer acrosomal membrane with the plasma membrane and their ultimate breakdown

the release of the soluble enzymes located within the acrosomal vesicle.

polymerization of g-actin (the globular form) within the subacrosomal region tof-actin (the filamentous form).

protein that mediates sperm binding to the surface of the egg

tip of the acrosomal process is covered with this protein

a tough noncellular layer interposed between the jelly coat and the plasma membrane of the egg

composed of glycoprotein and polysaccharide molecules

acrosomal enzymes with trypsinlike activity

After making its way through the vitelline coat, a sperm cell makes contact with the ______

The sperm receptor molecule consists of an _____

This region differs from species to species and is responsible for ensuing that only sperm of the same species fertilizes the egg

This region remains constant among different species, and it may serve to stimulate a signal transduction event that initiates the profound changes that affect the egg immediately after sperm-egg membrane fusion

a common feature of fertilization in all animals

first reported by Colwin and Colwin (1963)

Soon after sperm-egg fusion, a group of microvilli seem to engulf the head of the sperm, causing a bulge known as the ____

Where the sperm has made contact with the egg, the cytoplasm of the egg in many species bulges out in an elevated process called the_______

a membrane event that is set in place within 2 to 3 seconds and lasts for about 60 seconds, by which time the permanent (slow) block to polyspermy is established

difference in electrical potential generated by the plasma membrane of the egg

the rupture of cortical granules and the release of these contents into the space surrounding the egg (the perivitelline space)

new name given to the vitelline envelope after it has undergone the changes set in motion by the cortical reaction

located between the plasma membrane and fertilization membrane

powerful oxidizing agent

released by the egg at the time ofthe cortical reaction

mediates the chemical breakdown of H2O2 at the fertilization membrane

an effective way of maintaining the genetic integrity of the fertilized egg

In these species, polyspermy is normal and other means have been devised for inactivating and removing excess sperm from the fertilized egg

activate a program of events that is already patterned in the egg

begins with the influx of Na+ associated with the membrane depolarization of the fast block to polyspermy.

appears to be the main stimulus for the next major series of events (in activation of egg).

facilitate the biosynthesis of new membrane lipids

As the sperm nucleus becomes incorporated into the fertilization cone of the egg, the nuclear membrane begins to disintegrate.

As the phase of chromatin dispersion nears completion, a new membrane forms around what can now be properly called the ______

a radiating array of microtubules emanating from the original centrioles of the sperm

important in getting the male and female pronuclei together

plays a major role in guiding the migrations of the pronuclei

As the two pronuclei (male/female) come into contact with each other, their membranes fuse, leading to both maternal and paternal chromosome being enclosed in a single membrane.

Shortly after pronuclear fusion, the chromosomes _______ in preparation for the first cleavage division.

The first barrier the spermatozoa has the face

The apparent function of this acidity is to act as a bacteriostatic medium.

acts as an effective buffer against natural vaginal acidity

In ______, the semen coagulates shortly after insemination and forms a characteristic plug which prevents the backflow of spermatozoa

The next barrier in the path of the spermatozoa after the natural acidity of the upper vagina

may act as a valve which permits or prevents the passage of spermatozoa into the uterine tube

The spermatozoan response in which they orient themselves so that they move against a gentle current

As the spermatozoa are transported through the female reproductive tract, they are subjected to a poorly understood influence by the maternal tissues which enables them better to penetrate the membranes surrounding the egg. This phenomenon is called _______

The spermatozoa that are not directly involved in fertilization are ultimately removed from the female reproductive tract. Those in the uterine cavity are eventually swept through the cervix and into the vagina; those in the uterine tubes are ingested by phagocytic cells.

women who have the ________ are typically fertile

____(cells of the cumulus oophorus) surrounding the ovum is very important in egg transport

without this layer, ovum makes little progress

certain changes the ovum begins to undergo when liberated from the ovary

Motility lasts much longer than the ability to fertilize

fertilization occurs in the upper part of the uterine tubes

The spermatozoa must first penetrate the cells of the corona radiata and then the zona pellucida before they can make contact with the plasma membrane of the egg

a sperm-derived enzyme, that facilitates penetration through the corona radiata by dissolving extracellular matrix material around the cells.

When the spermatozoa reach the zona pellucida, specific molecules on the head of the sperm bind to species-specific ______, which consist of exposed parts of the ZP-3 molecule.

Further contact with the sperm head and other core regions of the ZP-3 molecule induce the _________

Capacitation is a prerequisite for this reaction

enzymes that facilitate the passage of the sperm through the zona pellucida

The localized fusion of portions of the outer acrosomal membrane with the overlying plasma membrane of the spermatozoon.

After the acrosome reaction, the spermatozoon digests a narrow pathway through the ______

a trypsinlike proteinase responsible for the spermatozoon's digestion of a narrow pathway through the zona pellucida

bound to the inner acrosomal membrane, which after the completion of the acrosome reaction is exposed to the surface of the head of the sperm

Once through the zona pellucida, the spermatozoon enters the _____________ between the zona and the plasma membrane of the ovum.

This reaction appears to cause a change in the plasma membrane of the sperm that allows it to fuse with other cell membranes

Contact is quickly established between the egg and sperm membranes and may be faciliated by the ______ projecting from the ovum.

As in the sea urchin, it is important for the egg to prevent polyspermy once it has been penetrated by the first sperm cell. This is accomplished by means of blocks to polyspermy

With sperm entry, the block to the second meiotic division of the egg is rapidly lifted and the second polar body is released, leaving a haploid female nucleus.

after entry into the egg, the nuclear membrane of the sperm breaks down, allowing the interaction between the nuclear contents of the sperm and the cytoplasm of the egg.

facilitate the extremely dense condensation of the nuclear chromatin that is required for proper packing of the nucleus of the mature sperm cell.

_______ ofthe sperm head is more complex than a mere exchange of protamines for histones

In the early stages of ______, the enzymatic breakdown of numerous disulfide bonds that keep the sperm chromatin condensed also occurs.

unfertilized eggs may become activated and develop into viable individuals as part of the normal life cycle

a reproductive strategy that involves development of a female gamete without fertilization

The sex of most animals is not determined at the time of fertilization

In mammals, the egg contributes an X chromosome to the process, whereas the sperm will contribute either an X or a Y chromosome, thus determining the sex of the zygote (XX for female and XY for male).

In this group of vertebrate, the chromosomal pairs of the male are alike, and those of the female show sexual differences.

The union of gametes and the genetic determination of sex constitute just the beginning of a long process of ________

chromatin mass

represents the morphological expression of a genetic control mechanism

The activity of only one X chromosome is required or permissible for normal development in either males or females.

Sex chromatin bodies are typically not seen during early embryonic cleavage

the paternal X chromosome is selectively inactivated in each of these extraembryonic tissues

The vertebrate body is bilaterally symmetrical

Vertebrate body three polar axes

The nucleus (germinal vesicle) is located near the ______

Both the size and the concentration of yolk platelets increase markedly toward the ______

In this group of vertebrate, the region of the animal pole will ultimately form the head and the vegetal pole will form the tail

(1) the activation of a specific region of vegetal cytoplasm and its displacement toward the cortex of the vegetal pole

(2) as cleavage occurs, the inclusion of the activated vegetal cytoplasm in cells (blastomeres) located near the gray crescent (future dorsal midline) area

(3) an inductive action of these cells on the neighboring cells in the equatorial region (between the animal and vegetal hemispheres)

sometimes called the dorsalizing center or Nieuwkoop center

the _________ axis can be predicted by the position of cells or cell layers relative to the yolk

________ becomes fixed after the fertilized egg has been in the uterus from 14 to 16 hours.