Genetics Synopsis
▫ Organisms are largely built of, and operate, via proteins. The artifactual rules for the construction and activities of proteins are coded in polynucleotides: DNA & RNA.
▫ DNA became the preferred form of storage for genetic data because it is stabler than RNA. Yet, in the process of extracting information content, DNA is first transcribed to RNA (transcription). RNA is then read (via translation) to render biological products, notably proteins.
▫ The macromolecules of life are characterized by their chemistry, information content, and spatial conformity. The origami of proteins and polynucleotides is critical to their performance. The intricacies of these compounds are astounding, as is the intelligence involved in their fabrication and employment.
History
▫ Heredity has long fascinated natural philosophers. Ancient Greek physician Hippocrates, Aristotle, and ancient Indian physicians writing in Charaka Samhita posited early hypotheses about biological inheritance.
▫ English naturalist Charles Darwin reprised Hippocrates’ hypothesis of pangenesis as the mechanism for heredity, whereupon offspring inherit holistic attributes of their parents through some atomic contrivance.
▫ Studying pea plants, Austrian monk Gregor Mendel observed genetic variations (alleles) in the early 1860s. He hypothesized them as heredity units.
▫ In imagining traits as embedded in biological dollops of heredity, Danish botanist Wilhelm Johannsen coined the term gene in 1909, well before the basics were understood.
▫ The dominant paradigm of genes as encoded units of heredity impeded apprehension of the molecular encyclopedia of life for nearly a century. Researchers continued thinking that spatially cogent genes and bodily traits had a strong correspondence long after evidence showed otherwise; whence the ignorant notion of “junk” DNA.
▫ Rather than adopt a more appropriate conceptual framework, geneticists inappropriately kept redefining old terms and adding new ones. Hence, the most intricate study of life at the level of molecular intimacy has become obtuse. The study of genetics continues to be full of surprises only owing to the illusion of knowledge.
Genetic Codes
▫ A gene is a conceptual entity, not a physical chemical complex. Genes are just ideas in the minds of geneticists.
▫ Genes were first conceived as molecular packages of trait heredity. They were later redefined as recipes for making proteins. Once other biological products were discovered to be important, and their templates stored in DNA, the definition of gene was extended to include them as non-protein coding genes. Now genes are conceived as molecular packages of trait heredity.
▫ Historically, a gene was assumed to be a certain strand of DNA that cogently carried a coding sequence for synthesizing a protein. Such facilely imagined localized genes are relatively rare, and their codes are not necessarily faithfully transcribed.
1st, physical trait data may be in multiple places. 2nd, translating genetic instructions into the intended product is a tortuous path, where much material goes unused or is waylaid in the expression process.
▫ DNA sequences act as instructions for specific manufactures. Gene expression is the process of using the information in a gene to synthesize a functional bioproduct, which is typically a protein.
▫ Prodigious research efforts have been expended toward gene mapping: pinpointing the loci of coding sequences for traits. The quest is mostly quixotic. Inherited traits are commonly the product of a network of genes, and gene expression is far more than just transcription at a gene’s locus. A trait may be the outcome of many genes, either activated or suppressed, in a long sequence of reactions leading to a result, with innumerable other factors in play.
▫ An allele is a gene variation at the same locus. Different alleles may result in different traits, but not necessarily. One allele may be dominant, while another recessive. A dominant allele may completely mask a recessive allele.
▫ A genome is the total complement of genes in a cell or organism. Individual cells have their own genomes. How that comes to be is not known.
▫ A prokaryotic cell has a single genophore stuffed with genetic material. Prokaryotes readily pick up new genetic material in non-genophore plasmid packages, which are exchanged with other microbes via horizontal gene transfer (HGT). Eukaryotes also employ HGT, though not nearly as frequently. A eukaryotic cell keeps its genome packed in chromosomes.
The genetic makeup of a multicellular organism is multifarious. Each cell has its own individualized genomic package (pergenome). Genetic variation among cells is termed chromosomal mosaicism.
▫ Evolutionary descent frequently involves carrying more genetic baggage. While over 90% of the genome of prokaryotes is employed, less than 2% of human genes are used for protein production.
DNA not directly recognized as used in protein production is termed noncoding. Such genetic material is often repetitive, sometimes with slight variations. This unobvious genetic material is employed in subtle ways that are just beginning to be appreciated.
▫ Algae, slime molds, fungi, and plants practice alternation of generations: alternate reproductive and genetic modes during their life cycle: asexual spore production while haploid, and sexual reproduction while diploid. A few animals may alternate reproductive modes – sexual and asexual – but all animals are always diploid.
▫ There is a genomic protection system that maintains the integrity of a cell’s genome, especially against damage that may be caused by self-serving jumping genes that otherwise proliferate.
Epigenetics
▫ Genes as the porters or heredity is an incomplete picture. Heredity also occurs epigenetically: outside genetic coding per se. Epigenetics is a cellular inheritance mechanism via gene regulation, without changing the structure of the DNA involved. Even for identical twins, epigenetic inheritance creates variations, thus rendering every organism genetically unique.
▫ An integral aspect of a cell’s life cycle, epigenetics is one way a cell adapts to its environment without changing genetic code. Through epigenetics, cellular memory may be passed to descendant cells. Epigenetic inheritance can be as stable as genetic inheritance.
▫ Gene regulation modulates the complicated process of gene expression. A DNA sequence is often not expressed as it was coded.
▫ There are many epigenetic mechanisms. Gene regulation comprises an interrelated network of information exchange among numerous molecular participants in the various processes of genic employment.
▫ Epigenetic marks are sometimes referred to as “switches,” implying that genes are either on or off. Instead, there are degrees of expression/suppression.
▫ An epigenome is the idea of a summated cellular set of instructions affecting access and expression of genes, including the timing of expression. A multicellular organism may have as many epigenomes as it has cells.
▫ Stress can cause epigenetic changes that are passed to the next generation. Exposure to pollutants results in epigenetic changes that can be inherited, even if offspring are never exposed to the pollutant.
▫ Homosexuality is epigenetically implanted during the development of a fetus. This epigenetic effect can last for generations.
▫ Meditation and a calm mind have a positive epigenetic effect and boost the immune system as well. There is no physiological explanation for how this is possible.
“DNA is not the be-all and end-all of heredity. Information is transferred from one generation to the next by many interacting inheritance systems.” ~ Eva Jablonka & Marion Lamb
