Origins Of Genetic Variation
Genetic variation is the difference in DNA sequences between individuals within a population. Variation occurs in germ cells i.e. sperm and egg, and also in somatic cells. Only variation that arises in germ cells can be inherited from one individual to another and so affect population dynamics, and ultimately evolution. Mutations;and;recombination;are major sources of variation.
Genetic Variation Definition Causes And Examples
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Genetic variation can be defined as the genetic makeup of organisms within a population change. Genes are inherited segments of DNA that contain codes for the production of proteins. Genes exist in alternate versions, or alleles, that determine distinct traits that can be passed on from parents to offspring.
What Is The Genetic And Environmental Variation
The genetic variation describes the difference in DNA between individuals. The two main sources of genetic variation are mutations and the combination of genes that result from sexual reproduction. The processes that direct or eliminates genetic variability is natural selection and genetic drift.
Environmental variation: Those differences in the physical characteristics of animals and plants that manifest by environmental factors and not by the genetic code. Factors such as food availability, hours of sunshine, and temperature can produce it. It can clearly be seen in plants.
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What Is Continuous Natural Selection
In a constant environment, natural selection will keep a population stable and essentially maintain the status quo. In a constant environment, if a new variationVariation: The differences among individuals in a population. arises that is more advantageous, the new trait will be perpetuated and the species will evolve.
Mating Patterns Are Important
When a population interbreeds, nonrandommating can sometimes occur because one organism chooses to mate with anotherbased on certain traits. In this case, individuals in the population makespecific behavioral choices, and these choices shape the genetic combinationsthat appear in successive generations. When this happens, the mating patternsof that population are no longer random.
Nonrandom mating can occur in two forms, with different consequences. One form of nonrandom matingis inbreeding, which occurs whenindividuals with similar genotypes are more likely to mate with each other ratherthan with individuals with different genotypes. The second form of nonrandommating is called outbreeding,wherein there is an increased probability that individuals with a particulargenotype will mate with individuals of another particular genotype. Whereas inbreedingcan lead to a reduction in genetic variation, outbreeding can lead to anincrease.
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Genetic Variation Between Species
While the above example discusses genetic variation between members of a population, the concept of genetic variation can be applied on a much grander scale. Consider for instance the Homeobox gene family. This family, known as the Hox genes for short, direct and coordinate the positions of body parts during development. These genes, or a variation of them is found among all bilaterally symmetrical animals. This includes everything from insects to fish and mammals. Scientist theorize that an early ancestor developed the Hox genes, which were quickly adapted to many forms of organism. The genetic variation represented in these genes is huge. They produce the different body types of most of the organism on Earth. However, they are still all related and the variance between them can be measured.
Worldwide Studies In Diverse Taxa
Adaptive selected SNPs widespread across life
Adaptive selected SNP polymorphism was found in maize domestication ; in the bacterium Thiomonas, genomic evolution appears by gain or loss of genomic islands in adaptation to arsenic-rich acid mine drainage and likewise in naturally occurring Arabidopsis thaliana . Adaptive chromosomes and SNP evolution of regulatory elements were identified in nine mammals and chicken ; in an altitudinal gradient in horses’ mtDNA ND6 ; in humans by disease-associated SNPs , and in high-altitude adaptation to hypoxia . By contrast, only scant evidence for positive selection, but abundant evidence for deleterious SNPs were described in a genomic analysis of the yeast Saccharomyces cerevisiae .
Significance Of Genetic Diversity In Nature
Evolution results from natural selection acting on diversity in populations, which ultimately stems from mutations. Extensive comparative analyses across genomes of model organisms elucidate diversity in nature . These new horizons partly unraveled the molecular structure, function, and evolution of life. Bioinformatics analyzed allozyme and DNA diversity at both coding and noncoding genomic regions permitting precise gene homologous alignment across taxa, the unraveling of gene and genome structure, expression, function, regulation, evolution, and the potential determination of the genetic basis of speciation and adaptation. In the early stages of allozyme studies of genetic diversity, it was shown that genetic diversity and heterozygosity varied nonrandomly between loci, populations, species, habitats, and life zones and were correlated with, and partly predicted by, ecological heterogeneity .
Human Genetic Variation And Disease
An important benefit of studying human genetic variation is that we can learn more about the genetic basis of human diseases. The more we understand the causes of diseases, the more likely it is that we will be able to find effective treatments and cures for them.
Some disorders are caused by mutations in a single gene. Most of these disorders are generally rare, but some of them occur at significantly higher frequencies in certain populations. For example, Ellis-van Creveld syndrome has an unusually high frequency in Pennsylvania Amish populations, and Tay-Sachs disease has a relatively high frequency in Ashkenazi Jewish populations. Albinism is another single-gene disorder that has a variable frequency. In North America and Europe, rates of albinism are approximately 1:18,000. In Africa, in contrast, the rates range from 1:5,000 to 1:15,000. Some African populations have estimated albinism rates as high as 1:1000. The photo below shows an African albino man from Mali, where there is a relatively high rate of albinism. High population-specific frequencies of single-gene disorders like these may be attributable to a variety of factors, such as small founding populations and a relative lack of gene flow.
Figure 6.2.3 This man from Mali exhibits the lack of pigmentation that is a hallmark of albinism.
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Which Of The Following Is An Example Of Genetic Variation
A persons skin color, hair color, dimples, freckles, and blood type are all examples of genetic variations that can occur in a human population. Examples of genetic variation in plants include the modified leaves of carnivorous plants and the development of flowers that resemble insects to lure plant pollinators.
Where Does Genetic Variation Come From
Mutations, the changes in the sequences of genes in DNA, are one source of genetic variation. Another source is gene flow, or the movement of genes between different groups of organisms. Finally, genetic variation can be a result of sexual reproduction, which leads to the creation of new combinations of genes.
Evolution And Adaptation To The Environment
Variation allows some individuals within a population to adapt to the changing environment. Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation. Some new alleles increase an organisms ability to survive and reproduce, which then ensures the survival of the allele in the population. Other new alleles may be immediately detrimental and organisms carrying these new mutations will die out. Neutral alleles are neither selected for nor against and usually remain in the population. Genetic variation is advantageous because it enables some individuals and, therefore, a population, to survive despite a changing environment.
Low genetic diversity in the wild cheetah population
The Evolution Canyon Model: Evolution In Action Across Life
The “Evolution Canyon” model reveals evolution in action across life at a microscale involving biodiversity divergence, adaptive evolution, and incipient sympatric ecological speciation across life . The model highlights species richness, genetic diversity and divergence, genomics, proteomics, phenomics, and metabolomics phenomena in diverse taxa by exploring genetic polymorphisms at protein and DNA levels and, recently, genome-wide gene expression and regulation . Genetic diversity and divergence reveal evolutionary dynamics of natural populations from bacteria to mammals exposed to sharp-interslope, ecologically divergent, tropical versus temperate microclimates on a xeric, tropical, “African” south-facing slope abutting with a mesic, temperate, “European” north-facing slope separated by 200 meters on average, e.g., as in Figure 1. Four “Evolution Canyons” are currently being investigated in Israel in the Carmel, Galilee, Negev, and Golan Mountains .
Remarkably, incipient sympatric ecological speciation was found across life from bacteria to mammals . The “Evolution Canyon” model represents the Israeli ecological analogue of the Galapagos Islands. Microclimatic selection overrides gene flow and drift and drives both interslope adaptive divergence and incipient sympatric ecological speciation at a microscale. Analyzing whole genomes with the next generation rapid high throughput techniques could unravel ecological-genomics dynamics at its best .
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How Science And Genetics Are Reshaping The Race Debate Of The 21st Century
Donald Trumps election as the 45th President of the United States has been marked by the brewing storms of racial conflicts. A rise;in racial incidents;ensued in the immediate aftermath of Trumps victory in November 2016. Since the beginning of 2017, over 100bomb threats have been made against Jewish community centers and schools. Trumps travel ban, signed in late January 2017, initially affected about 90,000 people from seven Middle Eastern countries; 87,000 of those banned were Muslims. Minorities such as;American Muslims and;black Americans;have expressed fears over racial relations under Trump. Undeniably, the topic of raceand racismhas gripped America and the world throughout.
Over the last decade, there have been hopes that the US has become a post-racial society, free of racial prejudice and discrimination. However, the most recent months indicate the contrary: race remains an incendiary issue. Race and racism are not new issues, but in todays 21st century Trump-era, discussions about race are distinct from those of the past in that they possess an entirely new dimension: that of genetics and DNA.
Genomic Diversity Of Humans
The decade from 2000 to 2010 involved breakthrough acceleration in genome science; numerous genomes have been sequenced and others are planned for complete sequences: 10,000 vertebrate genomes and 1,000 Drosophila genomes. Comparative genomics became a powerful tool for understanding evolution and genome function. Genetic diversity will be linked to function. Regulatory diversity in the noncoding genome will prove essential in functional processes. This will certainly revolutionize agriculture, medicine, and personalized medicine. Researchers hypothesized that small hotspots are stochastic but large-scale hotspots are constrained, correlated between humans and chimpanzees. The genetic structure and history of Africans and African-Americans based on 1,327 nuclear microsatellites and insertion/deletion markers revealed high levels of mixed ancestry in most 121 African populations, reflecting historical migration across the continent .
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Among Individuals Within A Population
Genetic variation can be identified at many levels. It is possible to identify genetic variation from observations of phenotypic variation in either quantitative traits ) or discrete traits ).
Genetic variation can also be identified by examining variation at the level of enzymes using the process of protein electrophoresis. Polymorphic genes have more than one allele at each locus. Half of the genes that code for enzymes in insects and plants may be polymorphic, whereas polymorphisms are less common among vertebrates.
Ultimately, genetic variation is caused by variation in the order of bases in the nucleotides in genes. New technology now allows scientists to directly sequence DNA which has identified even more genetic variation than was previously detected by protein electrophoresis. Examination of DNA has shown genetic variation in both coding regions and in the non-coding intron region of genes.
Genetic variation will result in phenotypic variation if variation in the order of nucleotides in the DNA sequence results in a difference in the order of amino acids in proteins coded by that DNA sequence, and if the resultant differences in amino acid sequence influence the shape, and thus the function of the enzyme.
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What Is Recombination
Recombination;is another major source of genetic variation Each of us has a mixture of genetic material from our parents. The mixing of this genetic material occurs during recombination when homologous DNA strands align and cross over. Recombination effectively shuffles maternal and paternal DNA, creating new combinations of variants in the daughter germ-cells .
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What Is Genetic Drift
Genetic drift is an evolutionary change in allelic frequencies of a population as a matter of chance. It occurs in very small populations but its effects are strong. It occurs due to an error in selecting the alleles for the next generation from the gene pool of the current generation. It does not occur due to any environmental influences.
In large populations allele frequency of the genes remain relatively stable because the genes are not affecting the fitness and do not have a natural selection pressure against the alleles.
Overview Of Human Genetic Variation
No two human individuals are genetically identical unless they are monozygotic twins. Between any two people, DNA differs, on average, at about one in one thousand nucleotide base pairs. We each have a total of about three billion base pairs, so any two people differ by an average of about three million base pairs. That may sound like a lot, but its only 0.1% of our total genetic makeup. This means that two people chosen at random are likely to be 99.9 per cent identical genetically, no matter where in the world they come from.
At an individual level, most human genetic variation is not very important biologically, because it has no apparent adaptive significance. It neither enhances nor detracts from individual fitness. Only a small percentage of DNA variations actually occur in coding regions of DNA which are sequences that are translated into proteins or in regulatory regions, which are sequences that control gene expression. Differences that occur in other regions of DNA have no impact on phenotype. Even variations in coding regions of DNA may or may not affect phenotype. Some DNA variations may alter the amino acid sequence of a protein, but not affect how the protein functions. Other DNA variations do not even change the amino acid sequence of the encoded protein.
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Genetic And Environmental Causes Together
Some features vary because of a combination of genetic and environmental causes. For example, tall parents will pass genes to their children for height. Their children have the genetic potential to also be tall. However, if their diet is poor then they will not grow very well: their environment also has an impact on their height.
Examples Of Gene Pool In Evolution:
- Individuals who are antibiotic-resistant are more likely to withstand any form of medical intervention in bacteria populations and live long enough to reproduce.
- The gene pool evolves over time to comprise only bacteria resistant to antibiotics.
- In this way, new strains of virulent bacteria are produced.
- A large number of plants that farmers classify as weeds are so tenacious because they have a diverse gene pool that helps them to adapt to a variety of environmental conditions.
- On the other hand, advanced hybrids also need very precise, even ideal conditions, because they have been bred to have a very small gene pool that prefers certain features, such as beautiful flowers or large fruits.
- It can be said that dandelions are superior to hybrid roses, on basis of size of gene pools.
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New Findings In Genetics Tear Down Old Ideas About Race
Estimating our ancestral composition down to 0.1% seem to suggest that there are exact, categorical divisions between human populations. But reality is far less simple. Compared to the general publics enthusiasm for ancestry testing, the reaction from scientists has been considerably more lukewarm. Research indicates that the concept of five races does, to an extent, describe the way human populations are distributed among the continentsbut the lines between races are much more blurred than ancestry testing companies would have us believe .
A landmark 2002 study by Stanford scientists examined the question of human diversity by looking at the distribution across seven major geographical regions of 4,000 alleles. Alleles are the different flavors of a gene. For instance, all humans have the same genes that code for hair: the different alleles are why hair comes in all types of colors and textures.
In the Stanford study, over 92% of alleles were found in two or more regions, and almost half of the alleles studied were present in all seven major geographical regions. The observation that the vast majority of the alleles were shared over multiple regions, or even throughout the entire world, points to the fundamental similarity of all people around the worldan idea that has been supported by manyother studies .
Figure 2:Case study of genetic variation between three scientists.
Fighting Racism With Understanding
Just as the alt-right is no longer an easily dismissed fringe group, their arguments have some factual basis, and cannot be swept aside as the babbling of the scientific illiterate. The alt-right is not clumsy in their use of science and genetics in their battle for their ideals. Those who oppose the alt-right, and other racist entities, must arm themselves with the same weapons: education, namely scientific and genetic literacy.
Mounting scientific evidence has shown that humans are fundamentally more similar than different from each other. Nonetheless, racism has persisted. Scientific findings are often ignored, or otherwise actively misinterpreted and misused to further racist agendas of extreme political groups. Opponents of these forces must, through their own education and awareness, combat these misleading interpretations and representations of scientific findings.
Today, the question of race is no longer merely a political and social issue: as science has rapidly advanced, it has become irrevocably intertwined. The genome contains powerful insights about our biology that could unite us as a species, but which could also be dangerous and divisive if used without understanding. As we look forward to 2017 and onwards, it becomes ever more important to understand what our DNA says about what it means to be human.
Vivian Chou is a Ph.D. candidate in the Biological and Biomedical Sciences program at Harvard Medical School.
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