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However, we had no concrete knowledge of the mechanism of variation. In other word, we did not know how the fittest are made. It turns out that the slight variations are small mutation in the genes. If such change is useful it will be passed onto future generations, otherwise it would be rooted out - the essence of natural selection. Any gene that is not useful will accumulate errors and become obsolete (fossilized). Figure 11-36h shows the types of DNA mutations that introduce trait variations. Table 11-03 lists mutations on specific gene(s) and the consequences. |
Figure 11-36h DNA Mutations [view large image] |
Species | Gene(s) | Function | Mutation | Selection for | MYA |
---|---|---|---|---|---|
Bacterium | Genes coding FlgL and homologues | Locomotion | Duplication and divergence | Flagellar components (rod, hook, filament) | >3000 |
Fish | Actinodin | Making fins' rigid fibres | Deletion | Walking on land | ~ 365 |
Giant Panda | T1R1 | Digesting protein | Insertion in the 3rd & deletion in the 6th exon | Change of diet to eating bamboo | ~ 75 |
Old world primates | Opsin | Colour vision | Duplication, fine tuning | Trichromatic vision | 30-40 |
Human | V1r olfactory receptor gene | Smell | 50% fossilized | Decreasing sense of smell | 30-40 |
Primates | TBXT | Style of locomotion | Alu Y deletion | No tail (see "tail-loss genetic") | ~ 25 |
Icefish | Globin gene | Making globin in hemoglobin | Fossilized and eroded | adaptation to cold water | 10-14 |
Antarctic fish | Gene for an enzyme | Anti-freeze | 3 repeating amino acids | Living in cold water | 10-14 |
Colobus Monkey | Ribonuclease gene for pancreatic enzyme | Breaking down RNA | Triple duplication and modification | Ruminating stomach for fermented leaves | ~ 6 |
Human | Switch for the AR gene | Facial whiskers and penile spines | Lost | Emotional Bonds (?) | ~ 5 |
Human | Switch for the GADD45G gene | Suppressing the development of cortex | Lost | Permiting the development of cortex | ~ 5 |
S. kudriavzevii | 7 galactose genes | Utilization of galactose | Lost | Living on decaying leaves | ~ 3 |
West Eurasian | SLC24A5 | Skin color | Single-nucleotide polymorphisms (SNP) | Lighter skin color for vitamin D absorption in reduced sunlight | 0.025 |
Stickleback fish | Genes coding armor plates | Protection in ocean | Reduction of gene number | Greater body flexibility in lake | 0.01 |
Stickleback fish | Switch for controlling Pitx1 gene expression | Making pelvic fin | Changed | Reduced pelvic skeleton | 0.01 |
Lactose-tolerant Populations | Intestinal lactase gene | Digest milk sugar lactose | Single base-pair change in regulatory sequence | Digest milk in adulthood | 0.009 |
Tibetans | HIF-2![]() |
Red blood cell production | Single-nucleotide polymorphisms (SNP) | Adoption to hypoxia environment | 0.003 |
Nigerian | LARGE | Response to infection | Single-nucleotide polymorphisms (SNP) | Lassa fever virus resistance | Recent |
Pupfish | Thyroid hormones from the thyroid gland | Morphologic changes | Thyroid suppression | Environmental adoption | 5 years |
Blind cave fish | Pigmentation gene | Body colour | Deletion of DNA text | Albinism | On-going |
Birds and mammals | MC1R | Coloration of body | Single letter change | Camouflage | On-going |
Pea plant | Gene for gibberellin oxidase | Growth-stimulating hormone | Single letter substitution, G ![]() |
Mendel's Experiment on height of plants | Man-made |
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(a) Mutation - Change in the sequence of one or more nucleotides in DNA (the mutation) would alter the structure of proteins or its production regulator generating a change of certain trait(s). As shown in Figure 11-36i(a), insertion of a 800-base-pair in the gene changes the skin of the pea from smooth to winkled (see evolution in colour vision). |
Figure 11-36i Evolutionary Theory [view large image] |
(b) Natural Selection - The change in trait(s) can exert a positive or negative influence on survival and reproduction depending mainly by the environment. For example, giraffe's long neck and legs are selected for getting more food (Figure 11-36i(b), also see evolution in action). |
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(1) Developmental Bias - Constraint for variation can be imposed by the inherently developmental processes within the organism. The processes may generate certain forms more readily than others. For example, the cichlid fishes in two different lakes have strikingly similar body shapes (Figure 11-36j(1)). (2) Phenotypic plasticity - It is the ability of an organism to change its phenotype in response to changes in the environment. Figure 11-36j(2) shows the change of colour in commodore butterflies during dry (left) and wet seasons. |
Figure 11-36j EES |
(3) Inclusive Inheritance - Extra-genetic inheritance occurs outside genetic expression, e.g., epigenetic changes, social behaviors, ecological constraints, etc. Figure 11-36j(3) shows a rodent maternal behavior transmitted through epigenetic changes; in this case it is the expression of genes by sexual hormones. |
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evolutionary changes have been located at three amino acid sites following the duplication. The mutations are retained because they appeared to have imparted a substantial advantage on the species (the old world primates) that bored them (see Figure 11-36l). The diagram shows those amino acid positions at 180, 277, and 285 within the opsin protein, which is bound to the light sensitive retinal. These differences are enough to shift the maximal light absorption from 560 nm for the red opsin to 530 nm for the green opsin. Note that mutation occurs with equal probability on all sites in the DNA; however, only those offering an advantage in survival will be retained. |
Figure 11-36k Natural Selection |
Figure 11-36l Mutation of Gene |
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geological scale, which offers ample time, many times over, for selection to shape a trait considering our ancestors' brains doubled in size in 1 million years (about 50,000 generations). Since change in the gene only becomes effective after passing onto the progeny, ultimately it is the number of generations that contributes to the speed of evolution with time serving only as an indicator. The evolution of simpler life appears to run faster because it can produce many generations within one year. It is crucial to appreciate that selection and mutation operate in nature every day. Every environment impacts continually upon the species that inhabit and reproduce within it. Evolution is an ongoing process. Selection acts only in the present, within a given environment. It cannot act on what a species no longer needs or uses. And it cannot act on what is not yet needed. Thus, fittest is a relative, transient status, not an absolute or permanent state. |
Figure 11-36m Evolution Time Scale [view large image] |
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The mechanism to induce the change in coloration of the peppered moth had not been identified until 2016 when one research detects the insertion of jumping genes into the cortex gene of the melanic moth (Figure 11-36n,a). Usually, the cortex gene is expressed to cleanup redundant proteins in cell cycle and has nothing to do with coloration. The relationship becomes clearer when another research on butterfly colors reveals that a version of the cortex gene is involved in the development of size, density and surface properties (including coloring) of the wing scales (Figure 11-36n,b,c). |
Figure 11-36n Peppered Moth Evolution [view large image] |
Ailment(s) | Body Part(s) | Modern Modification | Past Existence |
---|---|---|---|
Obesity | Body fat | Sedentary lifestyle | Active lifestyle in primates |
Hemorrhoids | Rectum | Sitting for long hours | Lot of walking in primates |
Back Pain | Lower back | Bipedalism | Body’s full weight was borne on four legs rather than two |
Sleep apnea | Throat | Throat becomes flexible for the ability to talk | Throat is not flexible for most mammals or reptiles |
Hiccups | Phrenic nerve | Phrenic nerve takes long path to control breathing in human, its interference can cause a spasm | Phrenic nerve takes shorter path from brain stem to gills in fish |
Hernias | Abdominal cavity | The gonads in the fetus of mammals migrate from upper to lower part of the body creating weak spot in body wall around the groin area | The gonads are located in the upper part of the body in fish and shark |
Mitochondrial diseases | An organelle In every cell | Many human mitochondrial diseases are related to gene change that interrupts the normal metabolic function | Diseases of such gene mutation in mitochondria can be duplicated in bacterium |
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starting from a symmetrical larva/juvenile, the skull is remodelled so that one eye migrates over the top of the skull to sit next to its other eye. Such change seems to mirror in the form of many living species with the pair of eyes in varying degree of togetherness. The lack of any intermediate specimen has led to attacks on natural selection and arguments for saltatory (leaping as opposite to gradual) change. The discovery of 47 million year old fossils (in 2008) of the Amphistium with its migrating eye never gets further than the dorsal midline, even in fully adult fishes has finally settled the dispute and confirmed that evolution of |
Figure 11-36o Morphological Change in Flatfish [large image] |
the specialized flatfish bodyplan was a gradual process induced by bottom-dwelling lifestyle (see Figure 11-36o, a - d for the transition of morphology in flatfish). |
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imagine. The process has now been demonstrated conclusively by an experiment starting way back in 1988 on an E. Coli population. A new trait finally emerges after 24 years or about 30000 generations. The new trait is the use of citrate (a salt of citric acid such as in lemon juice) as a nutrient in the presence of oxygen (labeled as cit+ in Figure 11-36p). In the beginning of the trial, the citrate can be absorbed as nutrient only in the absence of oxygen (labeled as cit- in Figure 11-36p). It is through the re-arrangement of a few DNA sequence and many duplications of such mutation that allows the new trait to establish itself in the E. Coli population. Figure 11-36p shows many dead ends until the condition is right for actualization (of the new |
Figure 11-36p Ecoli Evolution [large image] |
trait) and finally its refinement (maturity) after 40000 generations. This is Darwinian evolution in action albeit for small bacteria and only about one single trait. |
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It is noticed that some single cell organisms do not constrain by the rule of natural selection. They don't have complex organization, which requires a processing sequence to develop. Any unfavorable mutation that occurs during such process will likely be eliminated by internal selection. Thus, single cell organisms such as radiolaria (Figure 11-36q) and diatoms (Figure 11-36r) can exhibit 100 thousands different forms by random mutation without being culled by natural selection. |
Figure 11-36q Radiolaria |
Figure 11-36r Diatoms |
Darwin himself had mentioned this possibility but had forgotten to add a qualifier about small or simple. BTW, the holes in radiolaria are for the extrusion of the pseudopods, while it is for filtering in diatoms. |