Biological Sciences
Genes
Genes are the basic units of heredity that are passed from parents to offspring. They are made up of DNA and carry instructions for building and maintaining an organism. Genes determine traits such as eye color, height, and susceptibility to certain diseases. They can also influence behavior and other characteristics.
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10 Key excerpts on "Genes"
eBook - PDF- Andrew S. Reynolds(Author)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
In 1899, the botanist Hugo De Vries dubbed the suspected units of heredity “panGenes,” a term that would be abbreviated in 1909 by Wilhelm Johannsen to “gene.” Johannsen recommended this shorter word because it was, in his words, “free from any hypotheses . . . [and] expresses only the evident fact that . . . many characteristics of the organism are specified in the gametes by means of special conditions, foundations, and determiners which are present in unique, separate, and thereby independent ways – in short, precisely what we wish to call Genes.” Johannsen also introduced the terms “phenotype” and “genotype” to denote the physical characteristic (e.g., flower or eye colour) and its underlying genetic basis, respectively. For the next several decades the gene remained a hypothetical entity, but that did not stop scientists – now known as geneticists – from attributing to it, as Evelyn Fox Keller says, agency, autonomy, and causal primacy. What she calls the “discourse of gene action” made Genes responsible for all the chief elements of growth, development, and reproduction. Genes were spoken of as vital active agents and credited with transmitting traits (such as flower or eye colour, seed shape, or straight versus curly hair) from one generation to the next, and increasingly from the 1940s on for the more specific creation of enzymes and other proteins required for cell metabolism. In short, the import- ance of Genes was magnified to such an extent that the rest of the cell, with all 30 UNDERSTANDING METAPHORS IN THE LIFE SCIENCES its organelles and other cytoplasmic contents, were largely squeezed to the margins of the scientific field of view. The Molecular Biological Gene (1950s to Present): Information and Codes Genes acquired a new degree of reality and materiality with Watson and Crick’s 1953 papers in which they announced the double-helix structure of the DNA molecule and its implications for understanding heredity.
eBook - PDF- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
434 CHAPTER 10 The Nature of the Gene and the Genome 10.1 The Concept of a Gene as a Unit of Inheritance Our concept of the gene has undergone a remarkable evolution as biologists have learned more and more about the nature of inheritance. The earliest studies revealed Genes to be discrete factors that were retained throughout the life of an organism and then passed on to each of its progeny. Over the following century, these hereditary factors were shown to reside on chro- mosomes and to consist of DNA, a macromolecule with extraor- dinary properties. Figure 10.1 provides an overview of some of the early milestones along this remarkable journey of discov- ery, capped by the description of the double helical structure of DNA in 1953. In the decades that followed this turning point, a major branch of molecular biology began to focus on the genome, the collective body of genetic information that is pres- ent in a species. A genome contains all of the Genes required to “build” a particular organism. During the past decade or so, col- laborations by laboratories around the world have uncovered the complete nucleotide sequences of many different genomes, including that of our own species and the chimpanzee, our clos- est living relative. For the first time in human history, we have the means to reconstruct the genetic path of human evolution by comparing the corresponding regions of the genome in related organisms. We can learn which regions of our genome have been duplicated and which have been lost since our split from a common ancestor; we can observe which nucleotides in a particular gene or regulatory region have undergone change and which have remained constant; most importantly, we can infer which parts of our genome have been subject to natural selection and which have been free to drift randomly as time has passed.
eBook - PDF- Kostas Kampourakis(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
Genes are resources that provide cells with a generative plan about the development of the organism, and have a major role in this process through their products. This plan is the resource for the production of robust developmental outcomes that are at the same time plastic enough to accommodate changes stemming from environmental signals. Now, although I argue that Genes do not determine characteristics, and that Genes are neither our essences nor the ultimate explanations for the Regulation of cellular processes Regulation of gene expression Organism Organs Tissues Cells Molecular mechanisms Proteins Genes Figure 5.4 There are several kinds of interactions between the various levels of organization of organisms. Therefore, we need to consider not only what processes Genes affect, but also what affects their own function. 134 UNDERSTANDING Genes development of characteristics, it is indeed the case that changes in single Genes can have a big phenotypic impact. But, whereas a change in a gene may even disrupt a whole developmental process, the final outcome is in no way determined by this gene alone. Let us consider the SRY (sex-determining region Y) gene on the Y chromosome as an example. As mentioned in Chapter 2, all humans have 23 pairs of chromosomes, and men and women differ in that women have two X chromosomes and men have an X and a Y chromo- some. The default developmental outcome for the human embryo is to (a) (b) Gene A Phenotype 1 Gene B Phenotype 2 Gene C Phenotype 3 Gene A Gene B Gene C Phenotype 1 Phenotype 2 Environment 1 Environment 2 DEVELOPMENTAL PROCESSES Gene A Gene B Gene C Phenotype 2 Phenotype 3 DEVELOPMENTAL PROCESSES Figure 5.5 (a) A misrepresentation of gene function: a single gene determines a single phenotype. It should be clear by what has been presented in the present book so far that this is not accurate. (b) A more accurate representation of gene function that takes development and environment into account.
eBook - PDFThe Fundamentals of Brain Development
Integrating Nature and Nurture
- Joan Stiles(Author)
- 2008(Publication Date)
- Harvard University Press(Publisher)
Each discipline provided a different perspective on the question of in-heritance, and during the late nineteenth and the early twentieth cen-turies, each provided unique contributions to the evolving concept of the gene as the material, physical unit of intergenerational inheri-tance. Evolutionary biology focuses on the origins of species and species change over time. Population genetics takes a quantitative ap-proach, asking about frequencies and distributions of characteristics and traits within and across generations. The study of hereditary trans-mission focuses on single Genes and allelic variation. Developmental biology involves the study of the individual organism as it passes from larva to pupa or from embryo to fetus. The very brief history that follows touches on only a small sample of the ideas and discoveries that have contributed to the modern concept of the gene. Indeed, as will be clear, it is a concept that continues to change and evolve. The gene as it was first defined by Johannsen in 1911 is not the gene that Watson and Crick described in 1953, and the gene that Watson and Crick described is not the gene of modern de-velopmental geneticists. There are many threads to the story of the gene and many themes that could be emphasized. The account that follows will focus on three. The first is the overarching issue of ac-counting for both the constancy and the variability of biological inher-itance. It is the most ancient and the most persistent question and it is at the heart of the attempt to define the concept of a gene. The second theme concerns the level of scientific inquiry, because the perception of what a gene is can be influenced by the question the investigator has chosen to ask. An investigator who wishes to understand the source of a trait’s frequency and distribution in a population poses a different question than an investigator who seeks to account for individual vari-32 The Gene
eBook - PDF- D. Peter Snustad, Michael J. Simmons(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
They contain the complete nucleotide sequences of all genomes that have been sequenced to date, and they are continually updated. In addition, the NCBI web site contains tools that can be used to search for specific items of interest—gene and protein sequences, research articles, and so on. In Chapter 15, we will introduce you to some of these tools, and throughout this book, we will encourage you to visit the NCBI web site at the end of each chapter to answer specific questions. Broad Institute/www.genome.gov ◾ FIGURE 1.5 Researchers in a laboratory that performs DNA sequencing. Gregor Mendel postulated the existence of particulate factors—now called Genes—to explain how traits are inherited. Alleles, the alternate forms of Genes, account for heritable differences among individuals. James Watson and Francis Crick elucidated the structure of DNA, a macromolecule composed of two complementary chains of nucleotides. DNA is the hereditary material in all life forms except some types of viruses, in which RNA is the hereditary material. The Human Genome Project determined the sequence of nucleotides in the DNA of the human genome. Sequencing the DNA of a genome provides the data to identify and catalog all the Genes of an organism. KEY POINTS 6 Chapter 1 The Science of Genetics In all cellular organisms, the genetic material is DNA. This material must be able to replicate so that copies can be transmitted from cell to cell and from parents to offspring; it must contain information to direct cellular activities and to guide the development, functioning, and behavior of organisms; and it must be able to change so that over time, groups of organisms can adapt to different circumstances. DNA REPLICATION: PROPAGATING GENETIC INFORMATION The genetic material of an organism is transmitted from a mother cell to its daugh- ters during cell division. It is also transmitted from parents to their offspring during reproduction.
eBook - PDFKarp's Cell and Molecular Biology
Concepts and Experiments
- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
He sent Bea’s DNA off to have key members of the pathway sequenced and compared the returned sequences with those in the recently published human genome. Finding nothing, he expanded his search, enlisting the help of experts in academia and industry. The Nature of the Gene and the Genome 10.1 The Concept of a Gene as a Unit of Inheritance 10.2 The Discovery of Chromosomes 10.3 Chromosomes as the Carriers of Genetic Information 10.4 Genetic Analysis in Drosophila 10.5 The Structure of DNA 10.6 EXPERIMENTAL PATHWAYS: The Chemical Nature of the Gene 10.7 DNA Supercoiling 10.8 The Complexity of the Genome 10.9 THE HUMAN PERSPECTIVE: Diseases That Result from Expansion of Trinucleotide Repeats 10.10 The Stability of the Genome: Duplication 10.11 The Dynamic Nature of the Genome: “Jumping Genes” 10.12 Sequencing Genomes: The Footprints of Biological Evolution 10.13 Comparative Genomics: “If It’s Conserved, It Must Be Important” 10.14 The Genetic Basis of “Being Human” 10.15 Genetic Variation within the Human Species Population 10.16 THE HUMAN PERSPECTIVE: Application of Genomic Analyses to Medicine C H A P T E R O U T L I N E SOURCE: Courtesy of Leah Fasten Photography 366 10.1 • The Concept of a Gene as a Unit of Inheritance 367 10.1 The Concept of a Gene as a Unit of Inheritance Our concept of the gene has undergone a remarkable evolution as biologists have learned more and more about the nature of inherit- ance. The earliest studies revealed Genes to be discrete factors that were retained throughout the life of an organism and then passed on to each of its progeny. Over the following century, these hereditary factors were shown to reside on chromosomes and to consist of DNA, a macromolecule with extraordinary properties. FIGURE 10.1 provides an overview of some of the early milestones along this remarkable journey of discovery, capped by the description of the double helical structure of DNA in 1953.
eBook - PDFStochastic Processes In Genetics And Evolution: Computer Experiments In The Quantification Of Mutation And Selection
Computer Experiments in the Quantification of Mutation and Selection
- Charles J Mode, Candace K Sleeman(Authors)
- 2012(Publication Date)
- World Scientific(Publisher)
One current text book on molecular biology defines a gene as the entire set DNA segments of a nucleic acid sequence that are necessary for the syn-thesis of a functional polypeptide or molecule of RNA , see for example, Lodish et al. (2000). Evidently, this definition implies that the DNA sequences in a gene would include not only those coding for pre -mRN As and its flanking control regions but also for enhancers that are distant along a DNA sequence. However, even though they are distant in terms of base pairs, they may be close in terms of Euclidean distance in the three-dimensional chromatin space defined within a framework of Cartesian coordinates. As the sequencing of Genes, mRNA and whole genomes progressed, it became apparent that the simple operon model proposed Jacob and Monod turned out to be applicable to only prokaryotes and their phages, the viruses that attack them. It was found that Eukaryotes were different in many respects with respect to genetic organization and information flow. For example, the model of Genes as non-overlapping and continuous sequences of nucleotides was shown to be incorrect by the precise mapping of coding sequences of Genes. It was, in fact, found that some Genes overlap and share the same DNA sequence in different reading frames or even on the opposite strand. This discontinuous structure of Genes allows for the possibility that one gene may History of the Concept of a Gene 519 be completely contained within another’s intron, or one gene may overlap with another on the same strand without sharing any exons or regulatory sequences. The phenomenon of gene splicing was discussed in section 13.4 in con-nection with the preprocessing of mRNA . This phenomenon was discovered in 1977 and was reported in the papers Berget et al. (1977), Chow et al. (1977) and Gelinas et al. (1977).
eBook - PDF- Biswas, K P(Authors)
- 2018(Publication Date)
- Daya Publishing House(Publisher)
The application of genetic methods has made it possible to solve a number of problems specific to such sciences as biochemistry, physiology and embryology in a new and a more efficient way. By making use of hereditary changes and mutations, one can switch off and on almost all physiological processes, interrupt biosynthesis of metabolites in the cell, interrupt morphoGenesis and the like. The use of genetic methods in these sciences enables to obtain nearly any model necessary for investigation of one or another problem. Genetics plays quite a special role in the teaching of evolution. Inheritance variability and selection are the main factors of evolution. The This ebook is exclusively for this university only. Cannot be resold/distributed. role genetics played in consolidating Darwin’s ideas has already been known. Selection involves the effect of gene action, and it is owing to the evaluation of gene action expressed in characters and properties of the organism that selection of Genes occurs, creating a most valuable system, a genotype. That is how natural selection operates to create a definite genotype of the organism. Thus genetics has unraveled the main factors and mechanisms of interrelationship in evolution-inheritance, variability and selection. Thus, genetics is connected with all theoretical and applied biological sciences, including medicine and agriculture. Inheritance and variability is inherent in all nature, and this determines the position of genetics in the whole system of biological sciences. This ebook is exclusively for this university only. Cannot be resold/distributed.
eBook - PDF- Evelyn Fox Keller, Evelyn Fox KELLER(Authors)
- 2009(Publication Date)
- Harvard University Press(Publisher)
As Peter Portin observes, “Our knowledge of the struc-ture and function of the genetic material has outgrown the terminology traditionally used to describe it. It is arguable that the old term gene, essential at an earlier stage of the analysis, is no longer useful.” 35 William Gelbart, working at the forefront of molecular genetics, concurs in suggesting that the gene might be “a concept past its time.” “Unlike chromosomes,” Gelbart writes, “Genes are not physical ob-jects but are merely concepts that have acquired a great deal of historic baggage over the past decades.” To be sure, the concept of the gene has played a crucial role in leading us to 67 WHAT DOES A GENE DO? our present understanding of biological phenomena, but today, he suggests, “we may well have come to the point where the use of the term ‘gene’ . . . might in fact be a hin-drance to our understanding.” 36 There is more than a little irony in this present state of affairs, for never in the history of the gene has the term had more prominence, in both the scientific and the popular press. Daily, we are informed of the identification of new “disease-causing” Genes, with the list of corresponding “ge-netic” diseases growing steadily longer. 37 Similarly, we are told that much of human behavior that had previously been thought to be voluntary, or culturally induced, is a product of our Genes. Certainly, astonishing progress has been made in understanding the importance of genetic mutations in the incidence of many diseases (including a number of be-havioral disorders). A number of conditions have now been definitively tied to mutations in specific Genes. The simplest and most clear-cut cases are the single-gene disorders (Tay-Sachs, Huntington’s disease, cystic fibrosis, thalassemia, and phenylketonuria [PKU], among others). Such examples remain rare, however, and even in these clear-cut cases much remains to be understood about the processes that link the defective gene to the onset of disease.
eBook - ePubGenome Chaos
Rethinking Genetics, Evolution, and Molecular Medicine
- Henry H. Heng(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
With this historical basis, clearly, the meaning of the word “genome” should include both the whole genomic basis (chromosomes) and units of heredity (Genes). It is important to note that Winkler hoped to use this expression to link the genome to the foundation of the species (the whole genome system). Similarly, the genome was referred to as “a set of chromosomes” before the establishment of molecular genetics. Unfortunately, during the gene era and the dominance of the gene-centric view, the importance of the chromosome as a system organizer was ignored. The chromosome became primarily considered as a vehicle for Genes. The term “genome” has been applied specifically to mean the complete set of DNA molecules of a cell (both the nuclear genome and organelle genome that include the mitochondria and chloroplasts of a given species). Gradually, the “chromosome” portion of the genome has been chipped away; in practice, the definition of the term “genome” is now relegated to merely “a collection of Genes,”or “the whole of organism’s hereditary information encoded in its DNA (or, for some viruses, RNA).” Here are some representative examples: A genome is an organism's complete set of DNA, including all of its Genes. Each genome contains all of the information needed to build and maintain that organism. US National Library of Medicine (NIH) https://ghr.nlm.nih.gov/primer/hgp/genome The genome of an organism is the whole of its hereditary information encoded in its DNA (or, for some viruses, RNA). This includes both the Genes and the non-coding sequences of the DNA. https://simple.wikipedia.org/wiki/Genome A genome is the full set of instructions needed to make every cell, tissue, and organ in your body. Almost every one of your cells contains a complete copy of these instructions, written in the four letter language of DNA (A, C, T, and G). http://www.broadinstitute.org/education/glossary/genome All the genetic material in the chromosomes of a particular organism
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