Chapter 1

Question 1

Most patterns of embryogenesis are variations on six fundamental processes:

Answer 1

Fertilization Cleavage Gastrulation Organogenesis Metamorphosis Gametogenesis

Question 2

What is fertilization

Answer 2

Fusion of gametes (egg and sperm) into zygote. Fusion stimulates development further by activating the molecules necessary to begin cell cleavage and gastrulation.

Question 3

Describe the cleavage stage shortly.

Answer 3

A series of extremely rapid mitotic divisions, the enourmous volume of zygote cytoplasm is divided into numerous smaller cells (blastomeres).

Usually these form a sphere (blastula) signalling the end of this stage.

Question 4

What is a blastocoel:

Answer 4

Fluid filled cavity, important for cell movements during gastrulation.

Question 5

Describe gastrulation shortly.

Answer 5

A series of extensive cell rearrangements (cells move). Results in three germ layers in the embryo (endoderm, ectoderm, and mesoderm) that will interact and generate the organs of the body. Begins with the formation of a dimple (blastopore) roughly 180° from sperm entry point.

Question 6

Describe organogenesis shortly.

Answer 6

The cells interact with one another and rearrange themselves to produce tissues and organs. Chemical signals exchanged between layers ensure formation of specific organs at specific sites. Certain cells undergo long migration (from birth to final place), includes precursors for blood, lymph, pigment cells and gametes. Starts when the notochord signals the ectodermal cells above to form a tube and become the nervous system instead of epidermis.

Question 7

Describe the metamorphosis stage shortly

Answer 7

The process to become a sexually mature adult (most are not born that way). Most animals: larva stage is the young organism and the longest stage used for feeding or dispersal. In such species, the adult is a brief stage whose sole purpose is to reproduce. Most striking in frogs, going from a fully aquatic tadpole to a land living frog.

Question 8

Describe gametogenesis shortly.

Answer 8

The development of gametes, usually not completed until organism become physically mature, can take a long time. Germ cells are gametes - Their precursors are usually set aside early in development and is one of the first to undergo differentiation. To become mature, germ cells must be competent to complete meiosis.

Question 9

The adult organism eventually undergoes

Answer 9

senescence and dies. Its nutrients often supporting the early embryogenesis of its offspring, and its absence allowing less competition

Question 10

What is the vegetal hemisphere?

Answer 10

bottom portion of the egg, vegetal pga slow cell division rates, “immobile”

Question 11

What is the animal hemisphere?

Answer 11

upper half of egg, animal pga fast cell division rates

Question 12

What is a pronucleus ?

Answer 12

either female or male, haploid nucleus. Becomes “full” nucleus when fused together with another

Question 13

What is the blastopore?

Answer 13

Starts as a dimple, roughly 180° from sperm entry point, marks the future dorsal side of the embryo, expands to become a ring. Cells migrating through the blastopore become the mesoderm.

Question 14

mesoderm

Answer 14

“In between” endo- and ectoderm at end of gastrulation.

Question 15

ectoderm

Answer 15

“Outside” of embryo at end of gastrulation. The cells remaining on the outside of blastopore becomes the ectoderm, and expands to enclose the entire embryo.

Question 16

endoderm

Answer 16

“Inside” of embryo at end of gastrulation. The large, yolky cells that remain in the vegetal hemisphere (until encircled by expanding ectoderm) become the endoderm.

Question 17

Ectoderm becomes

Answer 17

epidermis, brain and nervous system

Question 18

Endoderm becomes

Answer 18

gut and respiratory systems

Question 19

Mesoderm becomes

Answer 19

connective tissue, blood, heart, skeleton, muscles, gonads and kidneys

Question 20

What is the notochord?

Answer 20

A rod of mesodermal cells in the most dorsal portion of the embryo, consists of cells that are important for the construction of the embryo, but die after having performed their tasks. Separates the embryo into left and right halves.

Question 21

Does the neural tube and notochord affect its neighbouring tissues?

Answer 21

Neural tube and notochord induce changes in their neighbours; mesodermal tissue adjacent becomes segmented into somites (precursors for back muscles, spinal vertebrae and dermis)

Question 22

Teratology is?

Answer 22

the study of birth defects

Question 23

Oviparity means?

Answer 23

born from eggs

Question 24

Viviparity means?

Answer 24

live birth

Question 25

Ovoviviparity means?

Answer 25

live birth hatched from egg inside the body, fx sharks

Question 26

Holoblastic division pattern

Answer 26

the entire egg is divided into smaller cells, fx frogs and mammals

Question 27

Meroblastic division pattern

Answer 27

only part of the egg is destined to become the embryo, the other (the yolk) serves as nutrition for the embryo, fx chicks

Question 28

Ex ovo Omnia means?

Answer 28

Ex ovo Omnia (all from the egg) – all animals originate from eggs

Question 29

Induction means?

Answer 29

no tissue is able to construct organs by itself; it must interact with other tissues.

Question 30

Do all animal embryos (vertebrates) develop in the same way?

Answer 30

By the beginning of neurulation all vertebrate embryos have converged on a common structure. As they develop beyond the neurula stage, however, the embryos of the different vertebrate groups become less and less like each other.

Question 31

Von Baer’s (4) laws: (late 1820’s)

Answer 31

The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group Less general characters develop from the more general, until finally the most specialized appear. The embryo of a given species, instead of passing through the adult stages of lower animals (simpler anatomies), departs more and more from them. Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo.

Question 32

“Phylotypic” stage – von Baer’s view, confirmed by recent research.

Answer 32

The embryos of the different classes of vertebrates all have a similar physical structure, and it appears that at this stage there is the least amount of difference among the genes expressed by the different vertebrate groups.

Question 33

Two major types of cells in the embryos:

Answer 33

• Epithelial cells – tightly connected to one another in sheets or tubes • Mesenchymal cells – unconnected to one another and operate as independent units

Question 34

Repertoire of various cellular processed involved in morphogenesis: (6)

Answer 34

• Direction and number of cell divisions – fx differences in dog legs between breeds • Cell shape changes – fx creation of tubes out of sheets or from epithelial to mesenchymal to allow individual cells to migrate away • Cell migration • Cell growth – cells change in size, fx sperm becoming smaller, eggs comparatively huge, many undergo asymmetric division; one small and one large daughter cell • Cell death – fx embryonic webbing between our fingers and toes, orifices of our mouth, anus and reproductive glands all form through apoptosis • Changes in composition of the cell membrane or secreted products – influencing neighbouring cells

Question 35

What is a fate map?

Answer 35

It maps the larval or adult structures onto the region of the embryo from which they arose, mammalian embryos among the most difficult to map pga develop inside another organism

Question 36

Discovering fate maps can be done through: (4)

Answer 36

• Direct observation – some organisms have naturally coloured cells • Dye marking – using vital dyes (stains but do not kill cells, is however diluted with each cell division) or fluorescent dyes (can still be detected many divisions later) • Genetic labelling – creating chimeric embryos, fx chicks and quails • Transgenic DNA chimeras – infection of donors with replication-deficient GFP expressing virus, desired cells for analysis are then transplanted into recipient and cells can be followed

Question 37

Homologous structures are

Answer 37

those organs whose underlying similarity arises from their being derived from a common ancestral structure, fx bird wing and human arm are homologous as forelimbs. Bat and bird wings are homologous as forelimbs, but not as wings.

Question 38

Analogous structures are

Answer 38

those whose similarity comes from their performing a similar function but different evolutionary origin, fx bat wing and bird wing, or bird and butterfly wing

Question 39

How many are born with a readily observable anatomical abnormality?

Answer 39

2-5% of human infants

Question 40

Malformations is?

Answer 40

abnormalities caused by genetic events (gene mutations, chromosomal aneuploidies and translocations)

Question 41

Disruptions are?

Answer 41

developmental abnormalities caused by exogenous agents (certain chemicals or viruses, radiation or hyperthermia) called teratogens (Greek – “monster formers”)

Question 42

How are the neural tube formed?

Answer 42

The neural precursor cells elongate, stretch, and fold into the embryo forming the neural tube, back of which is covered by the future epidermal cells

Question 43

Do all animals (vertebrates) start development the same way?

Answer 43

The eggs of birds, mammals, reptiles, fish and amphibians start development very differently because of the enormous differences in the sizes of their eggs.

Question 44

What is a teratogen?

Answer 44

exogenous agents that cause developmental abnormalities

Question 45

What is neurulation?

Answer 45

Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.

Question 46

Describe the neurulation process.

Answer 46

The process begins when the notochord induces the formation of the central nervous system (CNS) by signaling the ectoderm germ layer above it to form the thick and flat neural plate. The neural plate folds in upon itself to form the neural tube, which will later differentiate into the spinal cord and the brain, eventually forming the CNS

Question 47

Different portions of the neural tube form by two different processes, called primary and secondary neurulation, in different species. Describe the two.

Answer 47

In primary neurulation, the neural plate creases inward until the edges come in contact and fuse. In secondary neurulation, the tube forms by hollowing out of the interior of a solid precursor. Secondary neurulation occurs in the posterior section of most animals but it is better expressed in birds. Tubes from both primary and secondary neurulation eventually connect