On page 110, Shubin discusses the importance of the Hox genes and their relation to the body plan of an organism. He says specifically “if you make a fly that lacks a gene active in a middle segment, the midsection of the fly is missing or altered. Is there any way to change Hox genes that will lead to a positive outcome? Can we change the Hox genes of a person to make them grow taller or gain some sort of advantage? What are the ethical repercussions of this?
(Alex Sapozhnikov marijio@gmail.com)
Instead of merely editing the chromosomal order in Hox genes, duplication of these genes can serve as a beneficial change because it could potentially save the original gene pair from harmful mutations (Source 1). Since diploid organisms (containing 2n amount of chromosomes that arise from duplication in cellular mitosis) certainly have that extra gene pair that haploid organisms lack, this “backup” pair ensures that the gene can be safely mutated and tested in various combinations while the essential functions and structure of the original pair are kept intact (Source 1). Just as a reminder, mitosis is the process of nonsexual nuclear division that occurs in 4 phases (G1, S, G2 and M phases), while the M phase is broken down into 5 further stages before cytokinesis of the cellular membrane (prophase, prometaphase, metaphase, anaphase and telephase); meiosis is a divisional process that produces haploid, nonidentical daughter cells through two stages: Meiosis One of regular chromosomal division and Meiosis Two of sister chromatid division and re-pairing (Campbell 230-231). Some possible selective advantages of duplicating the Hox genes as a form of change are faster adaptive evolution over time should the duplicate pair acquire new functions from mutation; certain paralogous genes (genes in a species that have evolved from duplication of ancestral genes, such as olfactory receptors) can replace genes that are “knocked out” by harmful mutations and produce little to no effects on the organism’s phenotype after the changes; and lastly, that random loss of certain genes in a group of descendants after duplication and formation of genes in daughter cells after meiosis Stage Two can be counteracted by a genetic barrier that prevents interbreeding and possible spread of genetically inherited diseases through sexual reproduction (Source 1.)
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ReplyDeleteAlso, to answer this question, it is important to take a look at genetic mutation of Hox genes that have already occurred. The forelimb and hindlimbs of a tetrapod and pectoral and pelvic fins of fish are generally considered to be homologous parts, respectively, so the genetic mutation from marine organisms to amphibians and terrestrial animals could have come from changes to Hox genes. Previous research suggests that this change in body parts resulted from a mutation in the 5’ end of the Hoxd group of Hox genes, and that growth of limbs proved to be a beneficial selective advantage for land inhabitants (Source 3). Therefore, it is possible to change the Hox genes of a human or other animal to alter their physical phenotypes beneficially, but the problem with this logic is that changes would be occurring artificially in a laboratory as opposed to being caused by changes in the organism’s environment. The bioethics of such practice are questionable and dubious because of the involvement of either live human subjects or embryonic stem cells, as well as disastrous consequences of deliberately altering such a crucial sequence of genetic code through natural methods. As Shubin says, “mess with the Hox genes and you mess with the body in predicable ways” (Shubin 110); if harmful mutations occur frequently in these gene pairs already through natural selection and evolution, shouldn’t it be assumed that experimental changes could be equally if not MORE disastrous?
Sources:
1. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mutation_and_Evolution.html
2. Campbell, Mitosis/Meiosis Units
3. http://9e.devbio.com/article.php?ch=16&id=251
4. Neil Shubin
Christine Lin
choco_cat11@comcast.net