Mutant

“ Consequently, mutants can not be counted upon for experimental work, and their study scarcely needs to be considered. When a mutant is discovered by some fortunate chance, the mutable species from which it has sprung, and related species as well, should be subjected to the most critical surveillance, in the hope that new mutants will occur or the original one reappear. ”

“ Maybe it was a mutation back in the Old Stone Age who struck two flints together and made himself a fire. Maybe another mutant who dreamed up a wheel and took a stoneboat and changed it to a wagon.
Slowly, he said, it would have to be slowly. Just a little at a time. For if it were too much, if it were noticeable, the other humans would kill off each mutation as it became apparent. For the human race cannot tolerate divergence from the norm, even though mutation is the process by which the race develops.
The race doesn't kill the mutants any more. ”

“ But allowing that a mutant is capable of existence, its greatest handicap is the fact that it usually develops in the midst of a population so similar to itself that it is capable of interbreeding and will interbreed with this parental stock. If the mutant characters involve only a single pair of genes and if they are dominant, they will gradually disturb the conspectus of the parental species which, in the course of considerable time, should thus become a new species in the territory formerly occupied by the parental stock. ”

“ The benefit of increasing the network size is shown for three different combinations of forward and back mutation rates.Multiple Error Thresholds on a Binary Sequence of Length 40Each allele has two states—wild-type and mutant. The per base mutation rate from wild-type to mutant is identical for all loci. Back mutation from mutant to wild-type is not allowed. As mutant alleles fix in the population, the proportion of the sequence that can still mutate decreases. Multiple error thresholds exist because the effective mutation rate per genome drops as mutations accumulate. ”

“ The mutants came here and, gradually, the contamination of their genes would be localized, the cancer of mutation penned into one tiny area. Kesley wondered whether, on the day when the last mutant had left the Twelve Empires and entered Mutie City, the Dukes would bomb the city to shreds and thus restore mankind's genetic homogeneity. ”

“ We suppose that since life first put in its appearance on the earth there have been uncounted mutations, a vastly greater number than are now represented by determiners. Many of the mutants could not compete with their brothers and sisters of ordinary descent and so promptly died, but occasionally it might happen that a mutant would be as well fitted for life as its relatives, in which case it would establish itself, and in course of time become ancestor to a whole line like itself. ”

“ THE ISOLATION OF SPECIES
It now remains to show how such mutant races as we have noted in the preceding sections of this study may be transformed into such large and relatively uniform populations as satisfy our concepts of species.
A mutant individual is still far from constituting a species. Its survival depends in the first place upon the condition that the new, mutant characters shall not interfere with the health of the organism. ”

“ Radioactivity had caused mutation in some experiment, so the scientists were anxious to see what happened with these cattle.
"Genes determine the way an animal develops. Two mutant genes can start reactions that end up as a man with one leg, or maybe as a bull with the intelligence of an eight-year-old man. ”

“ It is, of course, hardly to be expected that any random change in as complex a mechanism as an insect would improve the mechanism, and as a matter of fact it is doubtful whether any of the mutant types so far discovered are better adapted to those conditions to which a fly of this structure and habits is already adjusted. ”

“ While severe mutant alleles that eliminate protein function represent the null state and confer lethality, hypomorphic alleles simply reduce protein function below an optimal level, resulting in a phenotype recognized as disease. In this manner, lethal genes can have mutations that only reduce protein function and therefore present as disease in the human population, allowing for inheritance of these more mild alleles in genetic diseases. ”

“ It is smaller than the normal mesothorax and its wings are imperfectly developed, but the bristles on the upper surface may have the typical arrangement of the normal mesothorax. The mutant shows how great a change may result from a single factor difference. ”

“ The factorial mutant answers neither the endurance test nor the intersterility test of a genuine species. It would, doubtless, be going too far to regard all such mutant forms as examples of germinal degeneracy, but it cannot be denied that all of them, when compared to the wild type, are in the direction of unfitness, none of them being viable and prosperous under the severe conditions obtaining in the wild state. ”

“ By examining mutations in these organisms, one can identify candidate genes that cause disease in humans, and develop models to better understand human disease and gene function. A fundamental roadblock for analysis is, however, the lack of a computational method for describing and comparing phenotypes of mutant animals and of human diseases when the genetic basis is unknown. ”

“ On a priori grounds there is no reason why several mutative changes might not take place in the same locus of a chromosome. If we think of a chromosome as made up of a chain of chemical particles, there may be a number of possible recombinations or rearrangements within each particle. Any change might make a difference in the end-product of the activity of the cell, and give rise to a new mutant type. It is only when one arbitrarily supposes that the only possible change in a factor is its loss that any serious difficulty arises in the interpretation of multiple allelomorphs. ”

“ In any case, a mutation which suppresses a character is not, as we have seen, a specific change, but merely one of the varietal order, which does not result in the production of a genuine new species. The factorial mutant with a vestigial wing or eye belongs to the same species as its wild or normal parent stock. Moreover, neither disuse nor natural selection has the slightest power to induce mutations of this kind. ”

“ For if the mutant and the plus race are alike as regards the modifiers, but differ only in the main factor, then no change in variability should result from intercrossing them, but only alternative conditions as regards the main factor. ”

“ Amongst the new mutant factors there may be some whose chief effect is on the character that the breeder is already selecting. Such a modification will be likely to attract attention. Superficially it may appear that the factor for the original character has varied, while the truth may be that another factor has appeared that has modified a character already present. In fact, many or all Mendelian factors that affect the same organ may be said to be modifiers of each other's effects. ”

“ Another consideration, which disqualifies the factorial mutant for the rôle of a new species, is its failure to pass the test of interspecific sterility. When individuals from two distinct species are crossed, the offspring of the cross is either completely sterile, as instanced in the mule, or at least partially so. ”

“ The genetics data are conclusive as to the frequent occurrence of mutations in the laboratory; there are numerous records of the appearance of similarly mutant individuals in nature, but there is little satisfactory evidence that these are the individuals out of which new species are made. ”

“ In connection with the question of spreading of mutant genes in the race there is another consideration, seldom referred to, that may occasionally have some weight in accounting for the dispersal of genes. ”

“ These, like the mutants in Drosophila, are fully equipped at the start. Since they breed true and follow Mendel's laws it is possible to combine them with characters of the wild type or with those of other mutant races. ”

“ The woman stopped and blew her nose. "That's all, except that the boy was gone when I came back—and George was dead."
Derwin looked down at the hat on his lap and searched for a way to express what he wanted to say. At last he looked up. "Some people believe the mutants killed only people who were very sick—people who had no chance to live anyway, and probably wanted to die quickly?" ”

“ Our understanding of gene function is often informed by comparing the phenotypic consequences of mutation with the canonical “wild-type” in a single organism, as well as between mutants of orthologous genes in different organisms. In particular, model organisms have provided great insight into gene function in humans. The importance and need for automating these cross-species comparisons has become imperative as large-scale mutagenesis screens are conducted in model organisms. ”

“ The upper group in F2 should contain a larger proportion of homozygous mutants than in F1, and since the parents of F3 were chosen from this upper group of F2 offspring, it is not surprising that the 11 F3 offspring recorded up to this time all fall in the upper group. The mean of this upper group is remarkably constant through the three generations, [28] and the variability of the group as measured by its standard deviation is also low, namely, 0.19. This indicates that the mutant character is a strongly dominant unit in relation to the ordinary condition of the plus series. ”

“ The individual mutants thus find their chance of surviving considerably increased and, as soon as a slight change in the outward circumstances occurs, any mutation, which at the outset was in the minority as compared with the parent species, may slowly but surely become the majority. It is constantly getting a fresh supply from the parent species and, as soon as it shows itself better adapted to the circumstances, it may finally supplant the parent species entirely. ”

“ But they seem very reluctant to do so. There does seem to have been some [197] mutation among plants,—De Vries has discovered several such,—but in animal life where are the mutants? When or where has a new species originated in this way? Surely not during the historic period.
Fluctuations are in all directions around a center—the mean is always returned to; but mutations, or the progressive steps in evolution, are divergent lines away from the center. Fluctuations are superficial and of little significance ”

“ On account of the suddenness with which they appear, mutants do not lend themselves readily to natural experiment, and after they have once been discovered, inquiry into the causes and course of mutation is practicable only by means of habitat and control cultures. Among variable species, those are most promising that show a wide range of variation and are found in abundance over extensive areas. ”

“ Almost always the collections are arranged in such a way that the phenomena of variation are masked. Forms intermediate between two species are, if possible, sorted into separate boxes under a third specific name. If a species is liable to be constantly associated with a mutational form, the mutants are picked out, regardless of the circumstances of their origin, from the samples among which they were captured, and put apart under a special name. ”

“ Ordinary or factorial mutation does not, therefore, as De Vries imagined, produce new species. These mutants do, indeed, meet the requirement of permanent transmissibility, for their distinctive characters cannot be obliterated by any amount of crossing. Nevertheless, the factorial mutation falls short of being an empirical proof of evolution, because it is a varietal, and not a specific, change. In other words, factorial mutants are new varieties and not new species. ”

“ The authors of one study therefore conclude that essential genes are not human disease genes [9] , as mutations prevent viability. However, this assumption fails to consider the impact of alleles on gene function. Genes have been defined as essential due to the phenotype of mouse knockouts, which result from a deletion of the protein-coding region of the gene from the genome. These mouse mutants therefore are null alleles, and represent the phenotype caused by complete absence of functional protein. However, point mutations in these same genes do not necessarily fully remove protein function. ”

“ Other parameters are the same as for the right side of Figure 3: w1 = 3.0, w2 = 2, and k = 2. When Nμ ≪ 1, the above description does not hold. Mutations occur so rarely, that the population is very likely to fix or lose each mutation before the next one arises. In this case, it no longer makes sense to talk about a quasispecies—there is no mutation–selection balance, but instead a fixed type, the wild-type, with possibly some recent mutants. The wild-type essentially undergoes a random walk in genotype space, in which it tends to “hang out” more often in areas with high fitness [18] . ”

“ For zebrafish, the mutants express a variable and modifiable phenotype that consists of decreased eye size, reduced lens size, and malformation of the retina. Drosophila ey (a PAX6 ortholog) mutations cause loss of eye development. The genotypes shown are E15 mouse Pax614Neu/14Neu [2] , 5 day zebrafish pax6btq253a/tq253a [3] , human PAX6+/− [4] , and Drosophila ey−/− [5] . Current methodologies traditionally identify animal models on the basis of sequence orthology between the mutant animal model and a human gene. ”

“ You know they create mutants in dormant germinating cells. Now that them seeds been exposed they ain't worth a tinker's dam to anybody. They won't breed true. Lord only knows what kind of freaks and fiddle-di-diddles'll come up—if anything comes up at all. ”