Essential developmental biology slack pdf free

The previous edition of this title, published in , defined the terms and laid out the field for evolutionary developmental biology. This field is now one of the most active and fast growing within biology and this is reflected in this second edition, which is more than twice the length of the original and brought completely up to date. There are new chapters on major transitions in animal evolution, expanded coverage of comparative embryonic development and the inclusion of recent advances in genetics and molecular biology.

The book is divided into eight parts which: place evolutionary developmental biology in the historical context of the search for relationships between development and evolution; detail the historical background leading to evolutionary embryology; explore embryos in development and embryos in evolution; discuss the relationship between embryos, evolution, environment and ecology; discuss the dilemma for homology of the fact that development evolves; deal with the importance of understanding how embryos measure time and place both through development and evolutionarily through heterochrony and heterotrophy; and set out the principles and processes that underlie evolutionary developmental biology.

With over one hundred illustrations and photographs, extensive cross-referencing between chapters and boxes for ancillary material, this latest edition will be of immense interest to graduate and advanced undergraduate students in cell, developmental and molecular biology, and in zoology, evolution, ecology and entomology; in fact anyone with an interest in this new and increasingly important and interdisciplinary field which unifies biology.

With an emphasis throughout on the evidence underpinning the main conclusions, this book is suitable as the key text for both introductory and more advanced courses in developmental biology.

Because the inducing factor is produced in one place, diffuses away, and decays, it forms a concentration gradient, high near the source cells and low further away.

This results in a series of zones becoming set up, arranged at progressively greater distance from the signaling center. In each zone a different combination of developmental control genes is upregulated. Among other functions, these transcription factors control expression of genes conferring specific adhesive and motility properties on the cells in which they are active.

Because of these different morphogenetic properties, the cells of each germ layer move to form sheets such that the ectoderm ends up on the outside, mesoderm in the middle, and endoderm on the inside. Growth in embryos is mostly autonomous. Free-living embryos do not grow in mass as they have no external food supply. But embryos fed by a placenta or extraembryonic yolk supply can grow very fast, and changes to relative growth rate between parts in these organisms help to produce the final overall anatomy.

The whole process needs to be coordinated in time and how this is controlled is not understood. There may be a master clock able to communicate with all parts of the embryo that controls the course of events, or timing may depend simply on local causal sequences of events. Developmental processes are very evident during the process of metamorphosis. This occurs in various types of animal. Well-known are the examples of the frog, which usually hatches as a tadpole and metamorphoses to an adult frog, and certain insects which hatch as a larva and then become remodeled to the adult form during a pupal stage.

All the developmental processes listed above occur during metamorphosis. Examples that have been especially well studied include tail loss and other changes in the tadpole of the frog Xenopus , [24] [25] and the biology of the imaginal discs, which generate the adult body parts of the fly Drosophila melanogaster.

Plant development is the process by which structures originate and mature as a plant grows. It is studied in plant anatomy and plant physiology as well as plant morphology. Plants constantly produce new tissues and structures throughout their life from meristems [28] located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues.

By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born or hatches from its egg , it has all its body parts and from that point will only grow larger and more mature.

The properties of organization seen in a plant are emergent properties which are more than the sum of the individual parts. A vascular plant begins from a single celled zygote, formed by fertilisation of an egg cell by a sperm cell. From that point, it begins to divide to form a plant embryo through the process of embryogenesis.

As this happens, the resulting cells will organize so that one end becomes the first root, while the other end forms the tip of the shoot. In seed plants, the embryo will develop one or more 'seed leaves' cotyledons. By the end of embryogenesis, the young plant will have all the parts necessary to begin in its life. Once the embryo germinates from its seed or parent plant, it begins to produce additional organs leaves, stems, and roots through the process of organogenesis.

New York: John Wiley. Carlson, B. St Louis, MO: Mosby. Textbooks, mainly analytical Twyman, R. Oxford: Bios Scientific Publishers. Wolpert, L. Oxford: Oxford University Press. Gilbert, S.

Wilt, F. New York: W. Monograph Martinez-Arias, A. Reproductive technology and ethics Edwards, R. International Journal of Developmental Biology 41, — Austin, C. Braude, P. International Journal of Developmental Biology 45, — Maienschein, J. Embryos, cloning and stem cells. Hwang, W. Science , — Chapter 2 Common features of development Developmental biology is the science that seeks to explain how the structure of organisms changes with time.

Structure, which may also be called morphology or anatomy, encompasses the arrangement of parts, the number of parts, and the different types of parts. Parts may be large, such as whole organs, or small, down to the level of the organization of individual cells.

Development happens most obviously in the course of embryonic development as the fertilized egg develops into a complete organism. This book deals mainly with embryonic development.

But it should not be forgotten that development also occurs in postembryonic life. The larva will at some stage undergo a metamorphosis in which the body is remolded to a greater or lesser extent to form the adult. Of the model organisms considered in this book, Drosophila shows a drastic metamorphosis during which most of the adult body is formed from imaginal discs laid down in the larva. Xenopus also undergoes metamorphosis from a tadpole to the adult frog. Some animals are capable of asexual reproduction by forming buds, and this is usually associated with the ability to regenerate large parts of the body after loss caused by predators.

This is true for example of many hydroids and planarian worms. Regenerative ability is less evident in higher animals but some amphibians have the ability to regrow limbs and tails after amputation, and even in mammals there is a certain ability to repair tissue damage following wounding.

Some developmental events are also associated with cell turnover and differentiation which occur continuously in most types of animal. Each of these examples of development involves similar problems and they can loosely be classified into four groups: 1 Regional specification deals with how pattern appears in a previously similar population of cells.

For example, most early embryos pass through a stage called the blastula or blastoderm at which they consist of a featureless ball or sheet of cells. Somehow the cells in different regions need to become programmed to form different body parts such as the head, trunk, and tail. This often involves regulatory molecules deposited in particular positions within the fertilized egg determinants. In addition it always involves some intercellular signaling, called embryonic induction, leading to the activation of different combinations of regulatory genes in each region.

Processes of regional specification occur in early development, during the formation of individual organs, and in the course of metamorphosis or regeneration. There are more than different specialized cell types in a vertebrate body, ranging from epidermis to thyroid epithelium, lymphocyte, or neuron. Each cell type owes its special character to particular proteins coded by particular genes.

The study of cell differentiation deals with the way in which these genes are activated and how their activity is subsequently maintained. Cell differentiation continues throughout life in regions of cell turnover.

This depends on the dynamics of the cytoskeleton and on the mechanics and viscoelastic properties of cells. It is less well understood than 1 and 2. Again, the morphogenetic processes involved in formation of tissue microstructure persist into adult life. Although more familiar to the lay person than other aspects of development, it is currently the least well understood aspect in terms of molecular mechanisms.

With a few exceptions, such as the lymphocytes of the immune system, all the different cell types in the animal body retain a complete set of genes. This means that the regulation of gene activity is important for all four processes and occupies a central position in developmental biology.

Many techniques for the study of gene expression are described in Chapter 5. The best evidence that all cell types retain a complete set of genes is derived from experiments on the cloning of animals from the nucleus of a single cell. Common features of development u Genomic equivalence, cloning of animals In any animal the sperm and eggs and their precursor cells are known as the germ line.

All other cell types are called somatic cells. The germ-line cells have to retain a full complement of genes otherwise reproduction would be impossible.

It is generally accepted that virtually all the somatic cells in animals also contain the full complement of genes and that the differences between cells are due to the fact that different subsets of genes are active. The total DNA content of most somatic cell types is the same; and when examined for the presence of a particular gene by standard molecular biological methods, DNA from all tissues gives the same results.

The most persuasive evidence has been obtained from experiments in which a whole animal is created using a single nucleus taken from a somatic cell. Because most genes will be required at some stage of development, the fact that a differentiated cell nucleus can support the whole process implies that all the DNA is still present in that nucleus. The experimental procedure is known as cloning, but it should be remembered that the term cloning is also applied to the molecular cloning of genes, and to the cloning of cells in tissue culture, particularly important in the production of monoclonal antibodies.

Many types of animal embryo, including frogs, rabbits, cows, sheep, and mice, can be cloned by transferring a nucleus from an early embryo cell a blastomere back into a fertilized egg whose own nucleus has been removed Fig.

In such experiments it is important to have some means of distinguishing an animal arising from the donor nucleus from one arising from the original egg nucleus, in case it was not properly removed or destroyed. This is known as a genetic marker. For example the donor nuclei in the frog experiments were often taken from albino embryos lacking the gene for pigment synthesis.

Only if the embryos arising from the reconstituted eggs are albino can one be sure that they were indeed formed from the donor nucleus. In frogs, nuclear transplantation works progressively less well the more advanced the developmental stage of the donor nucleus.

It has been possible to obtain a small number of tadpoles using nuclei from indubitably differentiated epidermal cells from adult frogs, and this strengthened the case for the conservation of DNA in all somatic tissues, but the poor yields led most scientists to think that this was not a practical means for the cloning of animals. Recent advances in the ability to clone animals have come from those mainly interested in new routes to the genetic modification of farm animals.

Using both sheep and cattle it has become clear that it is relatively easy to clone complete animals using nuclei from somatic cells taken from fetuses, and in some cases from adults, even if the cells are grown in tissue culture for some time Fig.

The procedure is to isolate a mature oocyte commonly known as an egg from the ovary, and remove the nucleus by sucking it out with a fine glass pipette. The oocyte is UV radiation Unfertilized egg pigmented strain Blastula albino strain Injection of nucleus into enucleated egg Albino frog Fig.

The donor cells may be deprived of serum before use to ensure that they are not undergoing DNA replication. An electric pulse is administered which causes fusion of the oocyte and the somatic cell and hence reintroduces a nucleus into the oocyte forming a reconstituted egg. This is cultivated in vitro for a while, during which it divides several times and progresses to a stage known as the blastocyst.

It is then implanted into the uterus of a female who has been hormonally primed to prepare her for pregnancy. Although many eggs do not survive the rigors of cell fusion and reimplantation in the uterus, a percentage of transplanted blastocysts can develop to term and be born. These progeny are genetically clones of the animal which originally donated the nucleus.

For such experiments the genetic markers need to distinguish the cell line from both the recipient egg donor, in case the egg nucleus was not properly removed, and the foster mother, in case of accidental pregnancy, and for this purpose DNA polymorphisms distinguishing the relevant animal breeds are detected using the polymerase chain reaction.

There are in fact some well-known exceptions to the principle that all somatic cells contain the same genes. The antibodyforming genes of B lymphocytes and the T-cell receptor genes of T lymphocytes are known to undergo rearrangement at the DNA level and lose some genetic information in the process. Certain nematodes, although not Caenorhabditis elegans, shed chromosomes from some cell lineages during development. There are also a few examples where total copy number of genes may be altered.

Polyploidy, where the whole chromosome set is doubled or quadrupled, can occur in some mammalian tissues such as the liver. Polyteny, where DNA replication occurs repeatedly without chromosomal division, leading to giant chromosomes, occurs in some tissues in Drosophila. However, in general the activity of genes is regulated at the level of transcription and subsequent events, and not at the level of the DNA itself.

Gametogenesis Embryo culture Reimplantation in uterus of foster mother strain 3 Fig. The genetic material may come from a somatic cell or a tissue culture cell. Sexual reproduction means that the life cycle involves the union of male and female gametes to form a fertilized egg or zygote.

By definition the male gamete is small and motile and called a spermatozoon sperm , and the female gamete is large and immotile and called an egg or ovum. Each gamete contributes a haploid 1n chromosome set so the zygote is diploid 2n , containing a maternal- and a paternal-derived copy of each chromosome. The gametes are formed from germ cells in the embryo. The germ cells are referred to collectively as the germ line, consisting of cells that will or can become the future gametes, and all other cells are referred to as the somatic tissues or soma.

The importance of the germ line is that its genetic information can be passed to the next generation, while that of the soma cannot. For example, a germ-line mutation indicates a mutation in germ Common features of development u cells that may be carried to the next generation.

By contrast, a somatic mutation may occur in a cell at any stage of development and may be important in the life of the individual animal, but it cannot affect the next generation. It is often the case that the future germ cells become committed to their fate at an early stage of animal development. In some cases there is a cytoplasmic determinant present in the egg that programs cells that inherit it to become germ cells.

This is associated with a visible specialization of the cytoplasm called germ plasm. It occurs in C. It occurs in Drosophila, where cells inheriting the pole plasm become pole cells and later germ cells. It probably also occurs in Xenopus where there is a vegetally localized germ plasm. In other species there may be no visible germ plasm in the egg but germ cells still appear at an early stage of development. During embryonic development germ cells undergo a period of multiplication and will also often undergo a migration from the site of their formation to the gonad, which may be some distance away.

The gonad arises from mesoderm and is initially composed entirely of somatic tissues. After the germ cells arrive they become fully integrated into its structure, and in postembryonic life undergo gamete formation or gametogenesis.

At some stage in mid-development the key decision of sex determination is made and the gonad is determined to become either an ovary or a testis. The molecular mechanism of this is, somewhat surprisingly, different for each of the principal experimental model species, so it will not be described in this chapter.

But the upshot is that in the male the germ cells will need to become sperm and in the female they will need to become eggs. Unlike the other model organisms, C. However there are also male individuals of C. Meiosis The critical cellular event in gamete production is meiosis. This is a modified type of cell cycle in which the number of chromosomes is reduced by half Fig. As in mitosis, meiosis is also preceded by an S phase in which each chromosome becomes replicated to form two identical sister chromatids, so the process starts with the nucleus possessing a total DNA content of four times the haploid complement.

In mitosis the sister chromatids will separate into two identical diploid daughter cells. But meiosis involves two successive cell divisions. In the first the homologous chromosomes, which are the equivalent chromosome derived from mother and father, pair with each other. At this stage the chromosomes are referred to as bivalents, and each consists of four chromatids, two maternal-derived and two paternal-derived.

Hence, alleles present at two different loci on the same chromosome of one parent may become separated into different gametes and be found in different offspring. The frequency with which alleles on the same chromosome are separated by recombination is roughly related to the physical separation of the loci, and this is why the measurement of recombination frequencies is the basis of genetic mapping. Recombination can also occur between sister chromatids but here all the loci should all be identical since they have just been formed by DNA replication.

In the first meiotic division the four-stranded bivalent chromosomes will separate into pairs which are segregated to the two daughter cells. There is no further DNA replication and in the second meiotic division the two chromatids become separated into individual gametes.

It is a primary oocyte until completion of the first meiotic division and a secondary oocyte until completion of the second meiotic division. After this it is known as an unfertilized egg or ovum. Because in the model organisms considered here fertilization occurs before completion of the second division, it is technically an oocyte rather than an egg that is being fertilized.

Eggs are larger than sperm and the process of oogenesis involves the accumulation of materials in the oocyte. Usually the primary oocyte is a rather long-lived cell that undergoes a It should be noted that the terms haploid 1n and diploid 2n are normally used to refer to the number of homologous chromosome sets in the nucleus rather than the actual amount of DNA. Oogenesis The process of formation of eggs is called oogenesis Fig.

Following sex determination to female, the germ cells become oogonia, which continue mitotic division for a period. The germ cells are initially formed from a cytoplasmic determinant and during development they migrate to enter the gonad. Spermatogenesis generally results in the production of four haploid sperm per meiosis. Oogenesis generally results in the formation of one egg and two polar bodies PB1 has the same chromosome number but twice the DNA content as PB2.

Common features of development u considerable increase in size. Its growth may be assisted by the absorption of materials from the blood, such as the yolk proteins of fish or amphibians which are made in the liver.

It may also be assisted by direct transfer of materials from other cells. This is seen in Drosophila where the last four mitoses of each oogonium produces an egg chamber containing one oocyte and 15 nurse cells.

The nurse cells then produce materials that are exported to the oocyte. Animals that produce a lot of eggs usually maintain a pool of oogonia throughout life capable of generating more oocytes. Mammals differ from this pattern as they are thought to produce all their primary oocytes before birth.

In humans no more oocytes are produced after the seventh month of gestation, and the primary oocytes then remain dormant until puberty. Although this is the conventional view, there is recent evidence for some postnatal oogenesis in mice. Ovulation refers to the resumption of the meiotic divisions and the release of the oocyte from the ovary.

It is provoked by hormonal stimulation and involves a breakdown of the oocyte nucleus the germinal vesicle and the migration of the celldivision spindle to the periphery of the cell. The meiotic divisions do not divide the oocyte into two halves, but in each case into a large cell and a small polar body. The first meiotic division divides the primary oocyte into a secondary oocyte and the first polar body, which is a small projection containing a replicated chromosome set.

The second meiotic division divides the secondary oocyte into an egg and a second polar body, which consists of another small projection enclosing a haploid chromosome set. The polar bodies soon degenerate and play no further role in development. Spermatogenesis If the process of sex determination yields a male then the germ cells undergo spermatogenesis Fig.

Mitotic germ cells in the testis are known as spermatogonia. These are stem cells that can both produce more of themselves and produce cells whose destiny is terminal differentiation into sperm. After the last mitotic division the male germ cell is known as a primary spermatocyte.

Meiosis is equal, the first division yielding two secondary spermatocytes and the second division yielding four spermatids, which mature to become motile spermatozoa. Early development The process of fertilization differs considerably between animal groups but there are a few common features.

When the sperm fuses with the egg there is a fairly rapid change in egg structure that excludes the fusion of any further sperm.

This is called a block to polyspermy. Fusion activates the inositol trisphosphate signal transduction pathway see Appendix resulting in a rapid increase in intracellular calcium.

This causes exocytosis of cortical granules whose contents form, or contribute to, a fert- 11 ilization membrane; and also trigger the metabolic activation of the egg, increasing the rate of protein synthesis and, in vertebrates, starting the second meiotic division. The calcium may, in addition, trigger cytoplasmic rearrangements that are important for the future regional specification of the embryo, for example cortical rotation in Xenopus, or polar granule segregation in C. The sperm and egg pronuclei fuse to form a single diploid nucleus and at this stage the fertilized egg is known as a zygote.

A generalized sequence of early development is shown in Fig. A typical zygote of an animal embryo is small, spherical, and polarized along the vertical axis. The upper hemisphere, usually carrying the polar bodies, is called the animal hemisphere, and the lower hemisphere, rich in yolk, the vegetal hemisphere. The early cell divisions are called cleavages. They differ from normal cell division in that there is no growth phase between successive divisions. So each division partitions the mother cell into two half-size daughters.

The products of cleavage are called blastomeres. Cell division without growth can proceed for a considerable time in free-living embryos without an extracellular yolk mass. Embryos that do have some form of food supply, either mammals that are nourished by the mother, or egg types with a large yolk mass such as birds and reptiles, usually only undergo a limited period of cleavage at the beginning of development.

This is the stage of maternal effects because the properties of the cleavage stage embryo depend entirely on the genotype of the mother and not on that of the embryo itself see Chapter 3. Different animal groups have different types of cleavage Fig.

Where there is a lot of yolk, as in an avian egg, the cytoplasm is concentrated near the animal pole and only this region cleaves into blastomeres, with the main yolk mass remaining acellular. This type of cleavage is called meroblastic. Where cleavage is complete, dividing the whole egg into blastomeres, it is called holoblastic. Holoblastic cleavages are often somewhat unequal, with the blastomeres in the yolk-rich vegetal hemisphere being larger macromeres , while those in the animal hemisphere are smaller micromeres.

Each animal class or phylum tends to have a characteristic mode of early cleavage and these can be classified by the arrangement of the blastomeres into such categories as radial echinoderms , bilateral ascidians , rotational mammals.

An important type is the spiral cleavage shown by most annelid worms, molluscs, and flatworms. Here, the macromeres cut off successive tiers of micromeres, first in a right-handed sense when viewed from above, then another tier in a left-handed sense, and so on. Most insects and some crustaceans show a special type of cleavage called superficial cleavage.

Here only the nuclei divide and there is no cytoplasmic cleavage at the early stages. Thus, the early embryo becomes a syncytium consisting 12 u Chapter 2 Polar body Yolk a Zygote b Cleavage c Blastocoel d Blastula e Gastrula Ectoderm Mesoderm Archenteron cavity Endoderm f Three germ layers Head g Larva Segments one another, being bound by cadherins, and will usually have a system of tight junctions forming a seal between the external environment and the internal environment of the blastocoel.

Following the formation of the blastula, all animal embryos show a phase of cell and tissue movements called gastrulation that converts the simple ball or sheet of cells into a three-layered structure known as the gastrula. The details of the morphogenetic movements of gastrulation can vary quite a lot even between related animal groups, but the outcome is similar. The three tissue layers formed during gastrulation are called germ layers, but these should not be confused with germ cells.

Conventionally the outer layer is known as the ectoderm, and later forms the skin and nervous system; the middle layer is the mesoderm and later forms the muscles, connective tissue, excretory organs, and gonads; and the inner layer is the endoderm, later forming the epithelial tissues of the gut. The germ cells have usually appeared by the stage of gastrulation and are not regarded as belonging to any of the three germ layers.

After the completion of the major body morphogenetic movements most types of animal embryo have reached the general body plan stage at which each major body part is present as a region of committed cells, but is yet to differentiate internally. This stage is often called the phylotypic stage, because it is the stage at which different members of an animal group, not necessarily a whole phylum, show maximum similarity to each other see Chapter For example all vertebrates show a phylotypic stage at the tailbud stage when they have a notochord, neural tube, paired somites, branchial arches, and tailbud.

All insects show a phylotypic stage at the extended germ band when they show six head segments, three appendage-bearing thoracic segments, and a variable number of abdominal segments.

Segments, spines and spots are not necessarily found in all animals but represent a typical external anatomy. The color scheme of ectoderm green, mesoderm orange, and endoderm yellow is used throughout the book. At a certain stage the nuclei migrate to the periphery and shortly afterwards cell membranes grow in from the outer surface of the embryo and surround the nuclei to form an epithelium.

During the cleavage phase a cavity usually forms in the center of the ball of cells, or sheet of cells in the case of meroblastic cleavage. This expands due to uptake of water and becomes known as the blastocoel. At this stage of development the embryo is called a blastula.

The cells often adhere tightly to In order that the correct orientation of a specimen can be specified, it is necessary to have terms for describing embryos Fig. If the egg is approximately spherical with an animal and vegetal pole then the line joining the two poles is the animal—vegetal axis. The textbook consists of three pity that only six, rather than seven, excellent embryo- sections and a total of 20 chapters.

All chapters are pro- logical essays are presented, since the author did not vided with lists of references for further independent include in this list sea urchins, one of the classical spe- reading, mostly recent reviews published in the leading cies for developmental biology studies, although one international journals.

The book is very well illustrated cannot work with this species in the laboratory the by original black-white figures accessible at the site: whole year round. For exam- its significance for medicine and agriculture is outlined. It is well known that Ver- tebrata have the rank of subtype and include several This textbook has already been republished twice, in classes: Cyclostomata, Chondrostei, Teleostei, and , apparently without any modifications Amphibia, Reptilia, Aves, and Mammalia.

The following reasons are problems of ontogenesis in Metazoa.