![\"File:Adult](\"http:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/c\/cc\/Adult_Caenorhabditis_elegans.jpg\/800px-Adult_Caenorhabditis_elegans.jpg\")
<\/a><\/p>\nHow come humans are way more than twice as complex as this little nemotode?<\/p>\n
The key appears to be not in the genes themselves, but how the genes are regulated.\u00a0 Humans have about 3,000 transcription factors, whereas the worm has barely a thousand.<\/p>\n
A transcription factor is a protein that binds to a specific DNA sequence.\u00a0 This binding can change how that gene is transcribed into mRNA, hence the name ‘transcription factor’.\u00a0 As a quick reminder, a DNA sequence is transcribed into messenger RNA (mRNA), which then travels out of the nucleus of cell and into a ribosome.\u00a0 The ribosome translates the mRNA sequence into a protein.\u00a0 This is the central dogma of molecular biology.\u00a0 DNA -> mRNA -> protein.<\/p>\n
These transcription factors can basically do two things: block transcription or promote transcription.\u00a0 They often act in concert with other proteins and may rapidly increase transcription, slow it to a crawl, or stop transcription entirely.<\/p>\n
The transcription factors can respond to genetic or chemical signals that come from the organism or the environment.\u00a0 For example, the estrogen receptor transcription factor responds to estrogen secreted by the ovaries.\u00a0 The estrogen actually crosses the nuclear membrane and directly interacts with the estrogen receptor, which then (because of a shape change caused by the estrogen) can attach to a particular sequence of DNA and ‘turn on’ (cause transcription) of certain genes in the cell.<\/p>\n
Hox transcription factors are vitally important in development and body organization of an organism.\u00a0 By injecting, say a fruit fly egg, with Hox transcription factors, scientists can cause a mandible to turn into a leg or cause eyes to grow on the knees of the legs or other ‘monster’ effects.<\/p>\n
Human complexity is not based on the number of genes, but on their regulation.\u00a0 The number of genes is fairly constant in animals, but the transcription factors that control gene expression are the critical links and cause the massive developmental changes that produce our complexity.<\/p>\n
For example, we can take a eye development gene from a mouse, put it into a fruit fly and the fruit fly will develop perfectly normal eyes.\u00a0 The gene for eye development is basically the same in almost every animal on the planet.\u00a0 But the transcription factors that control when and how the eye genes are turned on can result in compound eyes of the fruit fly, the pin-hole camera eyes of a chambered nautilus, the vertebrate backward eye with it’s blind spot, or a cephalopod eye that’s just like a vertebrate eye, but without the blind spot.<\/p>\n
This also explains the development of different body plans.\u00a0 The vertebrate body plan that we humans have isn’t that different from the fish ancestors we came from.\u00a0 In fact, developmental studies have shown that the gill arches that appear in both mammal and fish embryos come from the same genes.\u00a0 However, different regulation results in fish getting gills and humans getting everything from the bones of the middle ear to the hyoid bones.<\/p>\n
Neil Shubin’s Your Inner Fish<\/em> describes a lot of these changes and does so very well.<\/p>\n","protected":false},"excerpt":{"rendered":"Humans are complex, no doubt about it.\u00a0 Are we more complex than a sperm whale?\u00a0 I would debate that (either…<\/p>\n","protected":false},"author":27,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7,24,28,6],"tags":[244,243,938,937],"class_list":["post-365","post","type-post","status-publish","format-standard","hentry","category-biology","category-creationism","category-genetics","category-science","tag-complexity","tag-development","tag-evolution","tag-science"],"_links":{"self":[{"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/posts\/365","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/users\/27"}],"replies":[{"embeddable":true,"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/comments?post=365"}],"version-history":[{"count":0,"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/posts\/365\/revisions"}],"wp:attachment":[{"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/media?parent=365"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/categories?post=365"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/skepticink.com\/smilodonsretreat\/wp-json\/wp\/v2\/tags?post=365"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"File:Adult](\"http:\/\/en.wikipedia.org\/wiki\/File:Adult_Caenorhabditis_elegans.jpg\")
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