Are twins different from clones or are they the same at the genetic level?
Twins are two sister clones generated in the same recombination event.
But if you examine them at an epigenetic level they are different, although their DNA sequence is the same.
Identical twins are individuals that are from the same original embryo.
Clones might be from the same individual, but the genetic information contained in the nucleus, is transferred to different eggs.
This can make more of a difference than you might expect. The egg contains mitochondria (some call these metachlorians). These contain DNA. There are substantial differences between individuals in regard to mitochondrial DNA. Identical twins share the same mitochondria.
When a nucleus from a somatic cell is transferred into an egg the reprogramming is rather variable. This leaves lasting differences.
The somatic cells used are the product of many cell divisions. A surprising number of mutations occur during this process. These are random and will again generate variation between the clones made from a single individual.
Many changes to the DNA need to occur to undo modification done during development. These kind of get done. Kind of one way one time, kind of another way a different time.
Identical twins will always be more alike than clones. You can see me making identical twins on youtube, if you search for wwwcanbeorg, no periods.
Monozygotic twins can be considered as clone for a certain period of development as they are derived from a single zygote. Twins acquire many genetic differences early in fetal development, due to mutations taking place in each twin after the splitting of the embryo. Monozygotic twins are genetically very similar but not exactly similar.
I am making a distinction between the terms clone and twins because that is the question posed.
Identical twins are more genetically and epigenetically similar. Clones, embryos and individuals generated by nuclear transplantation from a somatic cell to an enucleated egg, are less genetically identical, because of accumulated mutations during somatic cell division. These clones are substantially more epigenetically different than identical twins.
epigenetics is far more influenced by environment and stochastic factors. I would say that it is almost impossible to make a "perfect clone". by the term "perfect clone", I mean two identical cells in all respect. ie, same genome , epigenome, transcriptome, proteome, metabolome and fluxome. this is impossible due to the following reasons :
1. when a cell divide, molecules in the mother cells are not equally distributed to the daughter cells. especially molecules with small copy numbers.
2. copies of certain molecules in a cell are so small that they does not obey law of mass action. those molecules vary in standard kinetics and equilibrium.
3. finally each molecule in a cell are highly dynamic and heterogeneous with respect to their quantum state and vibrations which cannot be determined; practically limited by Heisenberg's uncertainty principle.
clones cannot have a 100% identical epigenome. Epigenome is dynamic unlike static genome.
Among the main '-omics' technologies, metabolomics is expected to play a significant role in bridging the phenotype-genotype gap, since it amplifies changes in the proteome and provides a better representation of the phenotype of an organism. However, knowledge of the complete set of metabolites is not enough to predict the phenotype, especially for higher cells in which the distinct metabolic processes involved in their production and degradation are finely regulated and interconnected. In these cases, quantitative knowledge of intracellular fluxes (rates of metabolic reactions in biological systems) is required for a comprehensive characterization of metabolic networks and their functional operation. These intracellular fluxes cannot be detected directly due to reasons from my previous comment, but can be estimated through interpretation of stable isotope patterns in metabolites. Moreover, analysis of fluxome by means of metabolic control theories offers a potentially unifying, holistic paradigm to explain the regulation of cell metabolism.
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