![Literature review
Variation may be shown in physical appearance, metabolism, fertility, mode of reproduction,
behavior, learning and mental ability, and other obvious or measurable characters (Britannica,
2019) for which mutation is the ultimate source, but mechanisms such as sexual reproduction
and gene flow contribute to it as well. The translation of genotype to phenotype is complicated
by gene interactions observed as epistasis, canalization, robustness, or buffering. Analysis of
double mutations in inbred experimental organisms suggests some principles for gene
interaction that may apply to natural variation as well (Hartman et. al., 2001). An individual’s
environment can also cause variation (BBC, 2020). For example, human height is genetically
controlled but actual height reached will depend on the nutrition available. However, fact has
been proven that phenotypic expression of variant alleles might be influenced differentially by
environment (Imasheva et. al., 1999), stochastic events (Adams & Arkin, 1999), and
interactions with multiple other genetic loci. Causes and the effects of variation in traits let
breeders to know about the performance, behaviour, longevity, and fertility of individuals in
their natural habitats, and helps to detect evolutionary processes operating at a variety of
ecological levels: within random-mating populations; within and among subpopulations
distributed over a species’ geographic range; and even among multispecies associations (Mazer
& Damuth, 2001).
Reference
BBC. (2020). Variation and natural selection (CCEA). Biology (Single Science) Genetics.
Retrieved from https://www.bbc.co.uk/bitesize/guides/zgdjk2p/revision/2
Britannica. (2019). variation. Britannica, The Editors of Encyclopaedia. Retrieved from
https://www.britannica.com/science/variation-biology
Hartman, J. L., Garvik, B., & Hartwell, L. (2001). Principles for the buffering of genetic
variation. science, 291(5506), 1001-1004.
Imasheva, A. G., Bosenko, D. V., & Bubli, O. A. (1999). Variation in morphological traits of
Drosophila melanogaster (fruit fly) under nutritional stress. Heredity, 82(2), 187-192.
Mazer, S. J., & Damuth, J. (2001). Nature and causes of variation. In Evolutionary Ecology:
Oxford University Press.
McAdams, H., & Arkin, A. J. T. G. (1999). Genetic regulation at the nanomolar scale: it’sa
noisy business. 15(2), 65-69.
Causes of Variation
Mutation
Withinpopulation
Meiosis
Withinindividual
Gamete
combinations
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Natural
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Random
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Gene flow
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Independent
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Crossingover
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Emigration
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Immigration
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Variation and causes of variation
- 1. Internal Assessment on the topic “Variation and causes of Variation” SUBMITTED TO Dr. Ajeet Kumar Jha SUBMITTED BY Roll no. Name Roll no. Name 21 Dipa Sharma 31 Kalyani Bhandari 22 Gaurab Neupane 32 Khemraj Subedi 23 Gresha Suwal 33 Khusbu Adhikari 24 Hemant Kumar Sahani 34 Krita Karki 25 Himani Chand 35 Madhukar Chaudhary 26 Ichchha Neupane 36 Mahesh Kumar Bhandari 27 Janak Bhandari 37 Manoj Singh Yadav 28 Jitendra Hamal 38 MD Mumtaz Aalam 29 Jiwan Bhatta 39 Meena Pandey 30 Kalyan Bhattarai 40 Meena Sunar
- 2. INTRODUCTION Variation is defined as any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of -environmental factors on the expression of the genetic potentials (phenotypic variation). In genetics, variation refers to an individual that possesses characteristics different from the others of the same kind. Genetic variation usually arises as a mutation in a gene that encodes a protein or an RNA. Variations may be reflected in the phenotype of the individual, e.g., a difference in size, color or pattern, or may be detectable only by DNA or protein sequencing. A given variant may be the result of changes in a single gene, or the consequence of interactions among multiple genes. Populations of the same species living in different parts of the world may be characterized by specific sets of variations. TYPES OF VARIATION S. N Continuous variation Discontinuous variation 1. Continuous variation is the combined effect of the many genes (known as polygenic inheritance) and is often significantly affected by environmental influences. A characteristic of any species with only a limited number of possible values shows discontinuous variation. Discontinuous variation is controlled by alleles of a single gene or a small number of gene. 2 E.g.: milk yield in cow is determined not only by their genetic makeup but is also significantly affected by environmental factors such as pasture quality and diet weather and comfort of their surroundings E.g.: blood group, sex, eye color. Blood group: In the ABO blood group system, only four blood groups are possible (A, B, AB or O). There are no values in between, so this is discontinuous variation 3. CAUSES OF VARIATION: CAUSES Genetic Phenotypic Major Others Randommating DNA Mutation Gene Flow Sexual Reproduction Non- Randommating CrossingOver Randomfertilization Environmental variance Heredity(G) Environment(E) G×E
- 3. Genetic variation: It refers to differences in the genetic make-up of individuals in a population. Genetic variation results in different forms, or alleles of genes. For example, if we look at eye colour, people with blue eyes have one allele of the gene for eye color, whereas people with brown eyes will have a different allele of the gene. Different causes of genetic variation are: a. DNA Mutation: DNA mutation causes genetic variation by altering the genes of individuals in a population. They may impact an individual gene or an entire chromosome. Mutation is the primary source of genetic variation, which is the raw material for evolution through natural selection. By modifying genes and alleles in a population, mutation results in genetic variation. Although mutations change an organism's genotype, they may not necessarily change an organism's phenotype. b. Gene flow: Gene flow leads to genetic variation as new individuals with different gene combinations migrate into a population. An important evolutionary force is gene flow: the flow of alleles in and out of a population due to the migration of individuals or gametes. While some populations are fairly stable, others experience more movement and fluctuation. c. Sexual reproduction: Sexual reproduction promotes variable gene combinations in a population leading to genetic variation. Genetic variation occurs as alleles in gametes are separated and randomly united upon fertilization. The genetic recombination of genes also occurs during crossing over or the swapping of gene segments in homologous chromosomes during meiosis Phenotypic variation: Phenotypic variation, then, is the variability in phenotypes that exists in a population. Different causes of phenotypic variation are: a. Heredity(H): The genetic make-up of an individual is fixed at the time of fertilization and remains the same for the rest of an individual's life. An individual's genetic make-up is determined by the genes that are passed down from one generation to the next. Thousands of genes exist in both individuals and their parents whose exact number is unknown. That’s why, only the identical twins produced by a single fertilized egg are genetically alike. b. Environment(E): Environment here includes sum total of all external factors affecting the individual like feeding, housing, husbandry practices etc. Environment does not directly change the genetic make-up, but determine the degree of expression, i.e., these factors modify the development and expression of inherent qualities. c. H*E interaction: Animals of a certain genotype may perform better in one environment than in other, i.e., one environment permits the expression of genetic character in a breed or strain while the other does not. This shows the importance of having the right breed or strain for a particular environment in order to obtain optimum performance. Causes of variation can be also classified on the basis of population level which is given below:
- 4. Literature review Variation may be shown in physical appearance, metabolism, fertility, mode of reproduction, behavior, learning and mental ability, and other obvious or measurable characters (Britannica, 2019) for which mutation is the ultimate source, but mechanisms such as sexual reproduction and gene flow contribute to it as well. The translation of genotype to phenotype is complicated by gene interactions observed as epistasis, canalization, robustness, or buffering. Analysis of double mutations in inbred experimental organisms suggests some principles for gene interaction that may apply to natural variation as well (Hartman et. al., 2001). An individual’s environment can also cause variation (BBC, 2020). For example, human height is genetically controlled but actual height reached will depend on the nutrition available. However, fact has been proven that phenotypic expression of variant alleles might be influenced differentially by environment (Imasheva et. al., 1999), stochastic events (Adams & Arkin, 1999), and interactions with multiple other genetic loci. Causes and the effects of variation in traits let breeders to know about the performance, behaviour, longevity, and fertility of individuals in their natural habitats, and helps to detect evolutionary processes operating at a variety of ecological levels: within random-mating populations; within and among subpopulations distributed over a species’ geographic range; and even among multispecies associations (Mazer & Damuth, 2001). Reference BBC. (2020). Variation and natural selection (CCEA). Biology (Single Science) Genetics. Retrieved from https://www.bbc.co.uk/bitesize/guides/zgdjk2p/revision/2 Britannica. (2019). variation. Britannica, The Editors of Encyclopaedia. Retrieved from https://www.britannica.com/science/variation-biology Hartman, J. L., Garvik, B., & Hartwell, L. (2001). Principles for the buffering of genetic variation. science, 291(5506), 1001-1004. Imasheva, A. G., Bosenko, D. V., & Bubli, O. A. (1999). Variation in morphological traits of Drosophila melanogaster (fruit fly) under nutritional stress. Heredity, 82(2), 187-192. Mazer, S. J., & Damuth, J. (2001). Nature and causes of variation. In Evolutionary Ecology: Oxford University Press. McAdams, H., & Arkin, A. J. T. G. (1999). Genetic regulation at the nanomolar scale: it’sa noisy business. 15(2), 65-69. Causes of Variation Mutation Withinpopulation Meiosis Withinindividual Gamete combinations [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Natural Selection [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Random geneticdrift [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Gene flow [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Independent assortment [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Crossingover [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Emigration [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.] Immigration [Grab your reader’s attention witha great quote from the documentor use this space to emphasize a keypoint.To place this textbox anywhere on the page,just drag it.]