Common misunderstandings of genetics

Last updated

During the latter half of the 20th century, the fields of genetics and molecular biology matured greatly, significantly increasing understanding of biological heredity. [1] [2] [3] [4] As with other complex and evolving fields of knowledge, the public awareness of these advances has primarily been through the mass media, and a number of common misunderstandings of genetics have arisen.

Contents

Genetic determinism

It is a popular misconception that all patterns of an animal's behaviour, and more generally its phenotype, are rigidly determined by its genes. Although many examples of animals exist that display certain well-defined behaviour that is genetically programmed, [5] these examples cannot be extrapolated to all animal behaviour. There is good evidence that some basic aspects of human behaviour, such as circadian rhythms [6] are genetically based, but it is clear that many other aspects are not.

In the first place, much phenotypic variability does not stem from genes themselves. For example:

  1. Epigenetic inheritance. In the widest definition this includes all biological inheritance mechanisms that do not change the DNA sequence of the genome. In a narrower definition it excludes biological phenomena such as the effects of prions and maternal antibodies which are also inherited and have clear survival implications.
  2. Learning from experience. This feature is obviously important for humans, but there is considerable evidence of learned behaviour in other animal species (vertebrates and invertebrates). There are even reports of learned behaviour in Drosophila larvae. [7]

A gene for X

In the early years of genetics it was suggested that there might be "a gene for" a wide range of particular characteristics. This was partly because the examples studied from Mendel onwards inevitably focused on genes whose effects could be readily identified; partly that it was easier to teach science that way; and partly because the mathematics of evolutionary dynamics is simpler if there is a simple mapping between genes and phenotypic characteristics. [8]

These have led to the general perception that there is "a gene for" arbitrary traits, [9] leading to controversy in particular cases such as the purported "gay gene". [10] However, in light of the known complexities of gene expression networks (and phenomena such as epigenetics), it is clear that instances where a single gene "codes for" a single, discernible phenotypic effect are rare, and that media presentations of "a gene for X" grossly oversimplify the vast majority of situations.

Genes as a blueprint

It is widely believed that genes provide a "blueprint" for the body in much the same way that architectural or mechanical engineering blueprints describe buildings or machines. [11] At a superficial level, genes and conventional blueprints share the common property of being low dimensional (genes are organised as a one-dimensional string of nucleotides; [12] blueprints are typically two-dimensional drawings on paper) but containing information about fully three-dimensional structures. However, this view ignores the fundamental differences between genes and blueprints in the nature of the mapping from low order information to the high order object.

In the case of biological systems, a long and complicated chain of interactions separates genetic information from macroscopic structures and functions. The following simplified diagram of causality illustrates this:

Genes → Gene expression → Proteins → Metabolic pathways → Sub-cellular structures → Cells → Tissues → Organs → Organisms

Even at the small scale, the relationship between genes and proteins (once thought of as "one gene, one polypeptide") [13] is more complicated, because of alternative splicing.

Also, the causal chains from genes to functionality are not separate or isolated but are entangled together, most obviously in metabolic pathways (such as the Calvin and citric acid cycles) which link a succession of enzymes (and, thus, gene products) to form a coherent biochemical system. Furthermore, information flow in the chain is not exclusively one-way. While the central dogma of molecular biology describes how information cannot be passed back to inheritable genetic information, the other causal arrows in this chain can be bidirectional, with complex feedbacks ultimately regulating gene expression.

Instead of being a simple, linear mapping, this complex relationship between genotype and phenotype is not straightforward to decode. Rather than describing genetic information as a blueprint, some have suggested that a more appropriate analogy is that of a recipe for cooking, [12] where a collection of ingredients is combined via a set of instructions to form an emergent structure, such as a cake, that is not described explicitly in the recipe itself. [14]

Genes as words

This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). Introns are regions often found in eukaryote genes which are removed in the splicing process: only the exons encode the protein. This diagram labels a region of only 40 or so bases as a gene. In reality most genes are hundreds of times larger and have several Introns, sometimes over 100. Gene Intron Exon nb.svg
This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). Introns are regions often found in eukaryote genes which are removed in the splicing process: only the exons encode the protein. This diagram labels a region of only 40 or so bases as a gene. In reality most genes are hundreds of times larger and have several Introns, sometimes over 100.

It is popularly supposed that a gene is "a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for synthesis of RNA" [15] and even some current medical dictionaries define a gene as "a hereditary unit that occupies a specific location on a chromosome, determines a particular characteristic in an organism by directing the formation of a specific protein, and is capable of replicating itself at each cell division." [16]

In fact, as the diagram illustrates schematically, genes are much more complicated and elusive concepts. A reasonable modern definition of a gene is "a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions." [17]

This kind of misperception is perpetuated when mainstream media report that an organism's genome has been "deciphered" when they mean that it has simply been sequenced. [18]

Ancestry and ethnicity

Genetic ancestry tests advertised by companies such as 23andMe and AncestryDNA do not actually reveal a person's geographical ancestral origins or determine their race and ethnicity, [19] [20] [21] only useful estimates to genetic ancestry and population groups. [22] They compare a person's DNA markers to that of modern populations collected in a company's database. A person's DNA markers being matched to a particular location does not necessarily indicate that their ancestors are from that location, due to the fact human populations have migrated all throughout history, and the geopolitical borders of modern nations are not the same as they were in the past. [23] There are no genes that are unique to specific ethnic groups, as ethnic groups are created by human society rather than genetics. The actual genetic variation that exists among humans does not correlate with socially defined ethnic and racial categories, [24] yet there are patterns of genetic variation in some population groups that are more common than others. [25] Genetic ancestry is distinct from genealogical ancestry; as an individual's genealogical ancestors become more distant, they will become less genetically related to those ancestors, and a greater number of other individuals across the world will share those same ancestors [26] [27] but can be used for specific connections and cases like detecting a close relative. [28] Underrepresented populations may not receive as accurate results with data that is less specific, [29] although as the technology improves with tools like mid-pass whole genome sequencing this narrative will likely change and improve. [30]

Related Research Articles

<span class="mw-page-title-main">Genetics</span> Science of genes, heredity, and variation in living organisms

Genetics is the study of genes, genetic variation, and heredity in organisms. It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working in the 19th century in Brno, was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene.

<span class="mw-page-title-main">Genome</span> All genetic material of an organism

In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA. The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as regulatory sequences, and often a substantial fraction of junk DNA with no evident function. Almost all eukaryotes have mitochondria and a small mitochondrial genome. Algae and plants also contain chloroplasts with a chloroplast genome.

<span class="mw-page-title-main">Human genome</span> Complete set of nucleic acid sequences for humans

The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the nuclear genome and the mitochondrial genome. Human genomes include both protein-coding DNA sequences and various types of DNA that does not encode proteins. The latter is a diverse category that includes DNA coding for non-translated RNA, such as that for ribosomal RNA, transfer RNA, ribozymes, small nuclear RNAs, and several types of regulatory RNAs. It also includes promoters and their associated gene-regulatory elements, DNA playing structural and replicatory roles, such as scaffolding regions, telomeres, centromeres, and origins of replication, plus large numbers of transposable elements, inserted viral DNA, non-functional pseudogenes and simple, highly repetitive sequences. Introns make up a large percentage of non-coding DNA. Some of this non-coding DNA is non-functional junk DNA, such as pseudogenes, but there is no firm consensus on the total amount of junk DNA.

A microsatellite is a tract of repetitive DNA in which certain DNA motifs are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. They have a higher mutation rate than other areas of DNA leading to high genetic diversity. Microsatellites are often referred to as short tandem repeats (STRs) by forensic geneticists and in genetic genealogy, or as simple sequence repeats (SSRs) by plant geneticists.

<span class="mw-page-title-main">Genomics</span> Discipline in genetics

Genomics is an interdisciplinary field of molecular biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, three-dimensional structural configuration. In contrast to genetics, which refers to the study of individual genes and their roles in inheritance, genomics aims at the collective characterization and quantification of all of an organism's genes, their interrelations and influence on the organism. Genes may direct the production of proteins with the assistance of enzymes and messenger molecules. In turn, proteins make up body structures such as organs and tissues as well as control chemical reactions and carry signals between cells. Genomics also involves the sequencing and analysis of genomes through uses of high throughput DNA sequencing and bioinformatics to assemble and analyze the function and structure of entire genomes. Advances in genomics have triggered a revolution in discovery-based research and systems biology to facilitate understanding of even the most complex biological systems such as the brain.

<span class="mw-page-title-main">Molecular genetics</span> Scientific study of genes at the molecular level

Molecular genetics is a branch of biology that addresses how differences in the structures or expression of DNA molecules manifests as variation among organisms. Molecular genetics often applies an "investigative approach" to determine the structure and/or function of genes in an organism's genome using genetic screens. 

<span class="mw-page-title-main">Single-nucleotide polymorphism</span> Single nucleotide in genomic DNA at which different sequence alternatives exist

In genetics and bioinformatics, a single-nucleotide polymorphism is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population, many publications do not apply such a frequency threshold.

<span class="mw-page-title-main">Comparative genomics</span> Field of biological research

Comparative genomics is a branch of biological research that examines genome sequences across a spectrum of species, spanning from humans and mice to a diverse array of organisms from bacteria to chimpanzees. This large-scale holistic approach compares two or more genomes to discover the similarities and differences between the genomes and to study the biology of the individual genomes. Comparison of whole genome sequences provides a highly detailed view of how organisms are related to each other at the gene level. By comparing whole genome sequences, researchers gain insights into genetic relationships between organisms and study evolutionary changes. The major principle of comparative genomics is that common features of two organisms will often be encoded within the DNA that is evolutionarily conserved between them. Therefore, Comparative genomics provides a powerful tool for studying evolutionary changes among organisms, helping to identify genes that are conserved or common among species, as well as genes that give unique characteristics of each organism. Moreover, these studies can be performed at different levels of the genomes to obtain multiple perspectives about the organisms.

<span class="mw-page-title-main">Gene</span> Sequence of DNA or RNA that codes for an RNA or protein product

In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and non-coding genes.

<span class="mw-page-title-main">Human genetic variation</span> Genetic diversity in human populations

Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles), a situation called polymorphism.

<span class="mw-page-title-main">Human Genome Project</span> International scientific research project

The Human Genome Project (HGP) was an international scientific research project with the goal of determining the base pairs that make up human DNA, and of identifying, mapping and sequencing all of the genes of the human genome from both a physical and a functional standpoint. It started in 1990 and was completed in 2003. It remains the world's largest collaborative biological project. Planning for the project started after it was adopted in 1984 by the US government, and it officially launched in 1990. It was declared complete on April 14, 2003, and included about 92% of the genome. Level "complete genome" was achieved in May 2021, with only 0.3% of the bases covered by potential issues. The final gapless assembly was finished in January 2022.

Human evolutionary genetics studies how one human genome differs from another human genome, the evolutionary past that gave rise to the human genome, and its current effects. Differences between genomes have anthropological, medical, historical and forensic implications and applications. Genetic data can provide important insights into human evolution.

<span class="mw-page-title-main">1000 Genomes Project</span> International research effort on genetic variation

The 1000 Genomes Project (1KGP), taken place from January 2008 to 2015, was an international research effort to establish the most detailed catalogue of human genetic variation at the time. Scientists planned to sequence the genomes of at least one thousand anonymous healthy participants from a number of different ethnic groups within the following three years, using advancements in newly developed technologies. In 2010, the project finished its pilot phase, which was described in detail in a publication in the journal Nature. In 2012, the sequencing of 1092 genomes was announced in a Nature publication. In 2015, two papers in Nature reported results and the completion of the project and opportunities for future research.

<span class="mw-page-title-main">Whole genome sequencing</span> Determining nearly the entirety of the DNA sequence of an organisms genome at a single time

Whole genome sequencing (WGS) is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's chromosomal DNA as well as DNA contained in the mitochondria and, for plants, in the chloroplast.

<span class="mw-page-title-main">Exome sequencing</span> Sequencing of all the exons of a genome

Exome sequencing, also known as whole exome sequencing (WES), is a genomic technique for sequencing all of the protein-coding regions of genes in a genome. It consists of two steps: the first step is to select only the subset of DNA that encodes proteins. These regions are known as exons—humans have about 180,000 exons, constituting about 1% of the human genome, or approximately 30 million base pairs. The second step is to sequence the exonic DNA using any high-throughput DNA sequencing technology.

<span class="mw-page-title-main">Reference genome</span> Digital nucleic acid sequence database

A reference genome is a digital nucleic acid sequence database, assembled by scientists as a representative example of the set of genes in one idealized individual organism of a species. As they are assembled from the sequencing of DNA from a number of individual donors, reference genomes do not accurately represent the set of genes of any single individual organism. Instead, a reference provides a haploid mosaic of different DNA sequences from each donor. For example, one of the most recent human reference genomes, assembly GRCh38/hg38, is derived from >60 genomic clone libraries. There are reference genomes for multiple species of viruses, bacteria, fungus, plants, and animals. Reference genomes are typically used as a guide on which new genomes are built, enabling them to be assembled much more quickly and cheaply than the initial Human Genome Project. Reference genomes can be accessed online at several locations, using dedicated browsers such as Ensembl or UCSC Genome Browser.

Cognitive genomics is the sub-field of genomics pertaining to cognitive function in which the genes and non-coding sequences of an organism's genome related to the health and activity of the brain are studied. By applying comparative genomics, the genomes of multiple species are compared in order to identify genetic and phenotypical differences between species. Observed phenotypical characteristics related to the neurological function include behavior, personality, neuroanatomy, and neuropathology. The theory behind cognitive genomics is based on elements of genetics, evolutionary biology, molecular biology, cognitive psychology, behavioral psychology, and neurophysiology.

<span class="mw-page-title-main">Variant of uncertain significance</span>

A variant of uncertainsignificance (VUS) is a genetic variant that has been identified through genetic testing but whose significance to the function or health of an organism is not known. Two related terms are "gene of uncertain significance" (GUS), which refers to a gene that has been identified through genome sequencing but whose connection to a human disease has not been established, and "insignificant mutation", referring to a gene variant that has no impact on the health or function of an organism. The term "variant' is favored in clinical practice over "mutation" because it can be used to describe an allele more precisely. When the variant has no impact on health, it is called a "benign variant". When it is associated with a disease, it is called a "pathogenic variant". A "pharmacogenomic variant" has an effect only when an individual takes a particular drug and therefore is neither benign nor pathogenic.

<span class="mw-page-title-main">Structural variation in the human genome</span> Genomic alterations, varying between individuals

Structural variation in the human genome is operationally defined as genomic alterations, varying between individuals, that involve DNA segments larger than 1 kilo base (kb), and could be either microscopic or submicroscopic. This definition distinguishes them from smaller variants that are less than 1 kb in size such as short deletions, insertions, and single nucleotide variants.

Personalized genomics is the human genetics-derived study of analyzing and interpreting individualized genetic information by genome sequencing to identify genetic variations compared to the library of known sequences. International genetics communities have spared no effort from the past and have gradually cooperated to prosecute research projects to determine DNA sequences of the human genome using DNA sequencing techniques. The methods that are the most commonly used are whole exome sequencing and whole genome sequencing. Both approaches are used to identify genetic variations. Genome sequencing became more cost-effective over time, and made it applicable in the medical field, allowing scientists to understand which genes are attributed to specific diseases.

References

  1. ↑ Watson J.D.; Crick F.H.C. (1953). "Molecular structure of Nucleic Acids" (PDF). Nature. 171 (4356): 737–8. Bibcode:1953Natur.171..737W. doi:10.1038/171737a0. PMID   13054692. S2CID   4253007.
  2. ↑ Crick FH; Barnett L; Brenner S; Watts-Tobin RJ (December 1961). "General nature of the genetic code for proteins". Nature. 192 (4809): 1227–32. Bibcode:1961Natur.192.1227C. doi:10.1038/1921227a0. PMID   13882203. S2CID   4276146.
  3. ↑ International Human Genome Sequencing Consortium (2001). "Initial sequencing and analysis of the human genome" (PDF). Nature . 409 (6822): 860–921. Bibcode:2001Natur.409..860L. doi: 10.1038/35057062 . PMID   11237011.
  4. ↑ Venter JC; Adams MD; Myers EW; et al. (2001). "The sequence of the human genome" (PDF). Science . 291 (5507): 1304–51. Bibcode:2001Sci...291.1304V. doi: 10.1126/science.1058040 . PMID   11181995.
  5. ↑ For example, see this discussion of the behaviour of the digger wasp
  6. ↑ Florez JC, Takahashi JS (August 1995). "The circadian clock: from molecules to behaviour". Ann. Med. 27 (4): 481–90. doi:10.3109/07853899509002457. PMID   8519510.
  7. ↑ Gerber B, Hendel T (December 2006). "Outcome expectations drive learned behaviour in larval Drosophila". Proc. Biol. Sci. 273 (1604): 2965–8. doi:10.1098/rspb.2006.3673. PMC   1639518 . PMID   17015355.
  8. ↑ Nowak, Martin (October 2006). Evolutionary Dynamics: Exploring the Equations of Life. Belknap Press. ISBN   978-0-674-02338-3.
  9. ↑ Bishop, Dorothy (9 September 2010). "Where does the myth of a gene for things like intelligence come from?". The Guardian . Retrieved 11 September 2010.
  10. ↑ "Doubt cast on 'gay gene'". BBC. 23 April 1999. Retrieved 29 June 2007.
  11. ↑ Dusheck J (2002). "The interpretation of genes". Natural History . 111: 52–9.
  12. 1 2 Dawkins, Richard (1996) [1986]. The Blind Watchmaker. New York: W. W. Norton & Company, Inc. p. 295. ISBN   978-0-393-31570-7.
  13. ↑ Evers, C. The One Gene/One Enzyme Hypothesis, National Health Museum, retrieved 12 July 2007
  14. ↑ Pistoi, S. DNA is not a Blueprint, [Scientific American], retrieved 19 February 2020
  15. ↑ gene. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved 30 May 2007, from Dictionary.com website
  16. ↑ gene. (n.d.). The American Heritage Stedman's Medical Dictionary. Retrieved 30 May 2007, from Dictionary.com website
  17. ↑ Pearson H (2006). "Genetics: What is a gene?". Nature. 441 (7092): 398–401. Bibcode:2006Natur.441..398P. doi: 10.1038/441398a . PMID   16724031. S2CID   4420674.
  18. ↑ e.g. The New York Times , "Genome of DNA Discoverer Is Deciphered". Retrieved 1 June 2007.
  19. ↑ Krimsky, Sheldon (2021). Understanding DNA Ancestry. Cambridge University Press. ISBN   978-1-108-84198-6.
  20. ↑ Jobling, Mark A.; Rasteiro, Rita; Wetton, Jon H. (26 January 2016). "In the blood: the myth and reality of genetic markers of identity". Ethnic and Racial Studies. 39 (2): 142–161. doi:10.1080/01419870.2016.1105990. hdl: 2381/33343 . ISSN   0141-9870.
  21. ↑ "Debunking Genetic Astrology". UCL Division of Biosciences. 20 August 2021.
  22. ↑ Peterson, Roseann E.; Kuchenbaecker, Karoline; Walters, Raymond K.; Chen, Chia-Yen; Popejoy, Alice B.; Periyasamy, Sathish; Lam, Max; Iyegbe, Conrad; Strawbridge, Rona J.; Brick, Leslie; Carey, Caitlin E.; Martin, Alicia R.; Meyers, Jacquelyn L.; Su, Jinni; Chen, Junfang; Edwards, Alexis C.; Kalungi, Allan; Koen, Nastassja; Majara, Lerato; Schwarz, Emanuel; Smoller, Jordan W.; Stahl, Eli A.; Sullivan, Patrick F.; Vassos, Evangelos; Mowry, Bryan; Prieto, Miguel L.; Cuellar-Barboza, Alfredo; Bigdeli, Tim B.; Edenberg, Howard J.; Huang, Hailiang; Duncan, Laramie E. (2019). "Genome-wide Association Studies in Ancestrally Diverse Populations: Opportunities, Methods, Pitfalls, and Recommendations". Cell. 179 (3). Elsevier BV: 589–603. doi:10.1016/j.cell.2019.08.051. hdl: 20.500.12648/8361 . ISSN   0092-8674.
  23. ↑ Lawton, Georgina; Ifama, Daisy (11 August 2018). "'It made me question my ancestry': does DNA home testing really understand race?". The Guardian.
  24. ↑ "AABA Statement on Race & Racism". bioanth.org.
  25. ↑ Allendorf, Fred W.; Funk, W. Chris; Aitken, Sally N.; Byrne, Margaret; Luikart, Gordon (10 February 2022). "Genetic Variation in Natural Populations". Conservation and the Genomics of Populations. Oxford University PressOxford. pp. 39–65. doi:10.1093/oso/9780198856566.003.0003. ISBN   0-19-885656-3.
  26. ↑ Raff, Jennifer. "Genetic Astrology: When Ancient DNA Meets Ancestry Testing". Forbes.
  27. ↑ Rutherford, Adam (12 November 2019). "Ant and Dec's DNA test merely tells us that we're all inbred". The Guardian.
  28. ↑ University, Stanford (17 October 2018). "New way to find relatives from forensic DNA". Stanford News. Retrieved 19 January 2024.
  29. ↑ Sciences, National Academies of; Division, Medicine; Policy, Board on Health Sciences; Genomics, Roundtable on; Health, Precision; Beachy, Sarah H.; Alper, Joe; Addie, Siobhan; Hackmann, Meredith (19 March 2020). "Exploring the Role of Diversity and Health Disparities in Consumer Genomics". National Academies Press (US). Retrieved 19 January 2024.{{cite web}}: |last3= has generic name (help)
  30. ↑ Emde, Anne-Katrin; Phipps-Green, Amanda; Cadzow, Murray; Gallagher, C. Scott; Major, Tanya J.; Merriman, Marilyn E.; Topless, Ruth K.; Takei, Riku; Dalbeth, Nicola; Murphy, Rinki; Stamp, Lisa K.; de Zoysa, Janak; Wilcox, Philip L.; Fox, Keolu; Wasik, Kaja A.; Merriman, Tony R.; Castel, Stephane E. (2021). "Mid-pass whole genome sequencing enables biomedical genetic studies of diverse populations". BMC Genomics. 22 (1). doi: 10.1186/s12864-021-07949-9 . ISSN   1471-2164. PMC   8559369 . PMID   34719381.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.