Modifications are changes or differences between organisms in the same species that are due to differences in their environment. This is in contrast to mutations, which are changes in the genomes of organisms. Environmental differences that can affect an organism's characteristics (phenotype) include substrate, light, warmth, stress, exercise, and so on. Modifications are typically not heritable, however in some cases epigenetic modifications can be inherited. In both cases, there is no change to the primary DNA sequence (genotype), rather an influence on gene expression which is the cause of the altered phenotype.
In heredity the genes of the parents are passed on to their offspring unchanged. That is why the organisms which carry the same genotype should be identical in every feature. However, this is not the case. Due to environmental conditions they can vary from each other up to a certain point. There are two types of modifications: the continuous modification and the switching modification.
To illustrate the modificability you can take a look at our cultivated plants. The harvest of those plants do not only depend on the quality of the seeds but also greatly on environmental factors like the condition of the soil, the nutrient content of the soil, the fertilization, the humidity and temperature as well as the interference of other plants.
If you take a lowland dandelion and plant half of it in the lowland and the other half in the mountains the result will be a dandelion with big leaves in the lowland and one with small leaves in the mountains. The reason is that in the lowland the environmental conditions are different from those in the mountains.
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