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Common misunderstandings of genetics

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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.

Genetic determinism

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Main article: 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

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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

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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

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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

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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]

References

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  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. ^ a b 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.
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