BIOL 21900 Chapter 50

Animal Development

Uterine contractions ____.

are controlled by positive feedback

Compared to other mammals, the human brain is unique with respect to its ____.

integrative capacity and degree of complexity

Morphology refers to the ____ of an organism.

appearance

At the cellular level, the development of an animal from a fertilized egg involves cell division by _____.

mitosis

Human development ____.

begins at conception

At the cellular level, the development of an adult animal from a fertilized egg involves ____.

mitosis, cell differentiation, and morphogenesis

The final body form of an animal is generated as differentiated cells settle into their appropriate sites; this process is called ____.

morphogenesis

Before zygotic genes become active, the stages of animal development are directed by the ____.

cytoplasmic determinants of the egg

The information directing the development of the fertilized egg is provided by ____.

the egg and sperm nuclei, mRNAs in the egg cytoplasm, and proteins in the egg cytoplasm

Most of the mRNA and protein molecules in the zygote are from the ____ because ____.

mother; the fertilizing sperm contributes essentially no cytoplasm to the zygote

How does the amount of yolk relate to the nourishment of the organism?

An egg with a large amount of yolk contains all of the nutrients for the embryo's development.

Eggs from which organism contain the lowest percentage of yolk?

humans

Unequal distribution of yolk and other components in a mature egg is termed ____.

polarity

In an egg, the ____ pole typically gives rise to surface structures and the anterior end of the embryo while the ____ pole gives rise to internal structures such as the gut and the posterior end of the embryo.

animal; vegetal

Yolk, when unequally distributed in the egg cytoplasm, is most commonly concentrated in the ____ half of the egg.

vegetal

The correct sequence of embryonic development is ____.

cleavage, gastrulation, and organogenesis

During mitotic cleavage. ____.

cell division occurs and the embryonic mass does not change

As embryonic cells divide during cleavage, the daughter cells ____.

become progressively smaller

Cleavage-stage cells are called ____, which form a solid ball or layer called a ____.

blastomeres; morula

As cleavage divisions continue, the ball or layer hollows out to form the ____.

blastula

Place the three primary cell layers of an embryo in order, from superficial to deep.

ectoderm —> mesoderm —> endoderm

Arrange the developmental stages in the proper order

morula —> blastula —> gastrula

During the process of ____, blastomeres undergo extensive cellular rearrangements to produce an embryo with three distinct primary cell layers.

gastrulation

Muscles originate from the ____.

mesoderm only

Which group of adult tissues is derived from the mesoderm?

muscles, bones, cartilage

The lining of the mouth and anus originate from the ____, while the lining of the respiratory tract originates from the ____.

ectoderm; endoderm

Cells capable of producing all the various types of cells of the adult are called ____ cells.

totipotent

During ____, the three germ layers rearrange to produce tissues and organs.

organogenesis

In ____, one group of cells causes or influences another nearby group of cells to follow a particular developmental pathway

induction

Place the cellular processes responsible for animal development in the correct order: ____.

induction —> determination —> differentiation

Apoptosis is ____.

programmed cell death

In sea urchins, the primary mesenchyme cells eventually become the ____.

mesoderm

During gastrulation in sea urchins, invagination produces a cavity called the ____.

archenteron

The blastopore is the ____.

opening of the archenteron at the vegetal pole

In sea urchin embryogenesis, the mouth is formed ____.

where the archenteron contacts the ectoderm

In ____, the gray crescent establishes the ____ axis of the body.

frogs; dorsal-ventral

During gastrulation in frog embryos, cells migrate into the blastopore by a process called ____.

involution

During frog gastrulation, cells of the ____ of the blastopore control blastopore formation.

dorsal lip

Which group of organisms has a pattern of gastrulation that is the most similar to humans?

birds

In bird embryos, the pathway for cell migration into the blastocoel is formed by the ____, while in frog embryos, the pathway for cell migration into the blastopore is formed by the ____.

primitive groove; dorsal lip of the blastopore

The extraembryonic membrane that secretes fluid around the developing embryo is the ____.

amnion

The chorion is produced from which primary tissue layer(s)?

ectoderm and mesoderm

In vertebrates, organogenesis begins with ____.

neurulation

In vertebrates, the central nervous system develops directly from the ____.

neural tube

In vertebrates, cells of the neural crest develop into ____.

bones of the inner ear, cartilage of the face, and cranial nerves

Which structure of the eye is matched appropriately with its developmental origin?

ectoderm —> cornea

When the optic vesicle contacts overlying ectoderm, developmental events are induced, leading to ____ in the developing lens

crystallin synthesis

Normally, gestation lasts for approximately ____ weeks in humans

38

A human embryo is first considered to be a fetus at ____ weeks.

8

Normally, human fertilization occurs in the ____.

oviduct

During early embryonic development, implantation into the uterine lining occurs at the ____ stage.

blastocyst

The outer single layer of cells of the blastocyst is called the ____.

trophoblast

Genetic testing performed on cells of the placenta is called ____, while a similar procedure that uses cells derived from the amniotic fluid is called ____.

chorionic villus sampling; amniocentesis

The pharyngeal arches contribute to the formation of the ____.

larynx and pharynx

As the period of fetal growth comes to an end, a steep rise in ____ levels directly causes ____.

estrogen; uterine cells to express oxytocin receptor genes

After childbirth, ____ in the mother.

prolactin stimulates the production of milk and oxytocin stimulates the secretion of milk

What determines the development of male or female sex organs in the human embryo?

genes on the Y chromosome

Which event occurs in a human fetus with the XX combination of sex chromosomes?

The gonads develop into ovaries

When the SRY gene of the Y chromosome becomes active (around 7 weeks), the ____.

Müllerian ducts disappear and the Wolffian ducts develop into male reproductive structures

Determination ____, while differentiation ____.

is a cell's commitment to a developmental fate; is a cell's development into specialized cell types

Cell differentiation occurs due to ____.

changes in gene expression in different cell types

Evidence that all differentiated cells contain the organism's complete genome is provided by ____.

the successful cloning of a sheep, Dolly

During differentiation, organs develop with different numbers of cells due to ____.

the variable length of mitotic interphase

Fate maps of C. elegans development reveal that all somatic cells of the adult are directly descended from ____ produced during early development.

five somatic founder cells

Apoptosis begins when ____ is inactivated.

CED-9

Removal of webbing between human fingers is an example of ____.

apoptosis

Tissues present during organ development that are not found in the fully formed organ are removed by ____.

apoptosis only

Experiments on selective adhesion between ectoderm, mesoderm, and endoderm derived from amphibian embryos demonstrated that ____.

ectoderm cells have positive affinity for mesoderm cells but negative affinity for endoderm cells

When a dorsal lip from a newt is attached to the ventral side of another embryo, it results in ____.

two attached newts

Whole-cell movements involve the coordinated activity of ____.

microtubules and microfilaments

Research indicates that ____ defects occur ____ often with multiple births than single births.

heart; more

Match each term to its appropriate definition: A fluid filled cavity within the blastula

blastocoel

Match each term to its appropriate definition: An early embryo that has three primary tissue layers

gastrula

Match each term to its appropriate definition: A solid ball of blastomeres

morula

Match each term to its appropriate definition: An opening that eventually becomes the anus or mouth

blastopore

Match each term to its appropriate definition: Series of mitotic divisions in which cycles of DNA replication and division occur without the production of new cytoplasm

cleavage

Match each term to its appropriate definition: Early structure formed during nervous system development

neural plate

Match each term to its appropriate definition: A hollowed ball of blastomeres

blastula

The material in the gray crescent of a frog embryo is necessary for normal development.

True

The nervous system structures develop from the ectoderm.

True

Cells that undergo apoptosis are essential to the organism into adulthood.

False

Maternal blood mixes directly with the embryo’s blood in the placenta.

False

The process of apoptosis can remove structures such as mammary tissue in male mammals.

True

The hormone progesterone triggers the smooth muscles of the uterine wall to begin the contractions of labor.

False

In a human fetus that has the XX combination of sex chromosomes, the gonads develop into ovaries.

True

List and briefly describe the four stages of whole-cell migration

In the first stage, the front and back ends of a cell becomes defined by a polarization process. In the second stage, the front end of the cell protrudes as actin microfilaments assemble into long, parallel bundles. In the third stage, the cell adheres to the surrounding extracellular matrix. In the fourth stage, adhesion at the rear end of the cell is released, and the cell migrates forward and adheres to a new attachment point.

What are cadherins?

Cadherins are cell-adhesion molecules. They are necessary for establishing and maintaining connections between cells, and they play a critical role in the organization of cells in the body.

What are the characteristics of the animal and vegetal poles of the egg?

The egg nucleus is typically located at the animal pole of the egg. The animal pole generally gives rise to surface structures and the anterior end of the embryo. The opposite end of the egg is called the vegetal pole and typically gives rise to internal structures such as the gut and the posterior end of the embryo. Yolk, when unequally distributed in the egg cytoplasm, is most commonly concentrated in the vegetal half of the egg.

What is the evidence that differentiation produces specialized cells without the loss of genes?

Research has indicated that selective gene loss does not occur in differentiated cells. First, if a nucleus from a fully differentiated frog cell is inserted into a fertilized egg where the nucleus has been destroyed, the egg will develop into a normal tadpole and adult frog. Second, the sheep, Dolly, was successfully cloned from an adult cell nucleus, which is only possible if the adult cells retain all of their genes.

Explain how the SRY gene induces the development of testes and the male reproductive tract.

The SRY gene becomes active in the seventh week of embryonic development. The protein encoded by the gene sets a molecular switch that causes the primitive gonads to develop into testes. The fetal testes then secrete two hormones, testosterone and the anti-Müllerian hormone (AMH). The testosterone stimulates development of the Wolffian ducts into the male reproductive tract, including the epididymis, vas deferens, and seminal vesicles. Testosterone additionally stimulates the development of the male genitalia. AMH stimulates Müllerian duct regression.

Describe the three stages of labor

In the first stage of labor, the contractions push the fetus further against the cervix, dilating it up to 10 cm in diameter. In response to cervix dilation, stretch receptors in the walls send nerve signals to the hypothalamus, which responds by stimulating the pituitary to secrete
more oxytocin. In turn, the oxytocin stimulates more forceful contractions of the uterus, pressing the fetus more strongly against the cervix, and further stretching its walls. The second stage of labor is the actual birth of the baby. Continued uterine contractions begin to push the baby through the cervix and the vagina. In the third stage of labor, continuing contractions of the uterus expel the placenta and any remnants of the umbilical cord and embryonic membranes as the afterbirth.

Describe the experimental evidence for the selective adhesion property of cells.

Easily recognizable cells from the primary cell layers of amphibian embryos were placed individually in alkaline solution, which caused the tissues to break down into single cells. Researchers then combined different mixtures of cells, such as ectoderm + mesoderm and
ectoderm + mesoderm + endoderm. When the pH was returned to neutrality, the cells did not remain segregated, but formed aggregates. In the ectoderm + mesoderm mixture, the ectoderm moved to the periphery of the aggregate, surrounding the mesoderm cells. In the
ectoderm + mesoderm + endoderm mixture, the ectoderm cells were located on the periphery, the endoderm cells were internal, and the mesoderm cells were between the other two cell types. The researchers concluded that the cells had selective affinity for each other; these properties result from cell surface molecules that give cells specific adhesion properties.

What is the immune function of the placenta in human embryonic development?

The placenta prevents fetal blood from entering the maternal bloodstream. The fetal blood circulation system remains closed, and nutrients and oxygen from the mother’s circulation pass into the circulation of the embryo by diffusion. Since the maternal and fetal blood
circulations do not directly mix, this prevents the mother from developing an immune reaction against cells of the embryo, which, because it is genetically different from the mother, may be recognized as foreign by the mother’s immune system