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The study of vertebrate embryonic development became a separate
science in the early 1800s thanks to advances in microscopy.
Embryologists collected and dissected specimens from chicken,
frogs, turtles, fish, mice as well as humans, observed and
documented the anatomy and physiology. These largely observatory
work produced many of the important concepts in modern
developmental biology, such as germ layers (von Baer, 1828), the
theory of natural selection (Darwin, 1859), and the Organizer
(Spemann and Mangold, 1934). After World War II, especially after
the demonstration of DNA as the genetic material and advancement in
recombinant DNA technology, the focus of studies shifted to the
cellular, molecular and genetic processes of development, the
mechanisms of regulation, and the basis for developmental defects
and diseases. In recent years, advancements in stem cell biology
and gene editing technology ushered vertebrate embryology into a
new era as scientists use the tools and paradigms of embryonic
development to tackle diseases of all ages, bridging the embryo and
the adult. There is a vast body of research on vertebrate
embryology, enough to fill a whole library. It is not the goal of
this book to provide a comprehensive picture. Rather, I draw an
extremely simplified sketch, a "tasting menu", of current research
topics. The book is organized into five sections. Section 1
illustrates a number of major research questions on the three
developmental stages - cleavage, gastrulation, and organogenesis.
Section 2 presents the frontiers in the study of genetic and
epigenetic regulation: the role of genetic interactions,
chromatin-based regulation, and non-coding RNAs. Section 3
describes the current research and application of stem cells.
Section 4 introduces the role of genetic and environmental factors
in developmental defects. Finally, Section 5 highlights the
exciting new field of gene editing, using TALENs and CRISPR/Cas9
technologies as two examples.
Genetic diversity, or the variety of genes within a species, plays
important roles in phenotypic diversity and the species' ability to
adapt to environments. Studies of genetic diversity mainly focus on
two areas. The first area is concerned with understanding and
characterizing genetic diversity in humans, animals, plants, and
microbes. The second focus area is exploiting genetic diversity for
the purposes of medicine, agriculture, and conservation. To help
readers appreciate the wide range of research questions on genetic
diversity and how molecular approaches are utilized to address
these questions, this book is organized into three chapters to
showcase selected studies of genetic diversity in humans, animals
and plants, and microbes, respectively. The post-genomic era
provides powerful tools for the studies of genetic diversity. For
example, as of 2016, the single nucleotide polymorphism (SNP)
database maintained by the National Center for Biotechnology
Information (NCBI) lists ~150 million SNPs. The huge amount of
available genomic information greatly facilitates genome-wide
association studies (GWAS). GWAS has been applied to the studies of
various human diseases including cancer, heart diseases and
diabetes. In agriculture, GWAS is used to identify genomic regions
associated with desirable breeding traits in cattle or agronomic
traits in plants. Thanks to the advancement in sequencing
technology, it has become feasible and increasingly routine to
sequence multi-gene panels, exomes, and whole genomes. These
approaches are being widely used for the investigation of genetic
variants-of-interest as well as genetic diagnosis. Gene panels
offer a quick way to interrogate a panel of genes that are known to
be associated with a specific disease or condition. Compared to
sequencing of gene panels, whole exome sequencing (WES) and whole
genome sequencing (WGS) cost more for each sample but generate much
larger amount of data such that the cost per variant is
significantly less. By interrogating millions of variants per
genome, WES/WGS can be very powerful in identify new variants that
are associated with diseases, disease risks, or prognosis. Another
important technological development is gene editing technology.
Genetic diversity in plants and animals provide the raw material
for crop and livestock breeders, respectively. Gene editing
technology greatly enhances the efficiency of breeding by allowing
breeders to create transgenic elite lines and manipulate multiple
loci simultaneously.
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