My question is simple. If I wanted to make an exact twin of an individual, will genetically engineering the DNA of the zygote to match with the individual suffice?
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1$\begingroup$ Can you please expand and better explain your questions? At the moment they are often hard to understand. $\endgroup$– Chris ♦Feb 18, 2015 at 13:20
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$\begingroup$ Edited. Is there any more doubts? $\endgroup$– arnabanimeshFeb 18, 2015 at 13:36
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$\begingroup$ Is it possible, from any cell of an individual? (speaking theoretically) Then are you saying it won't be an identical twin if just the DNA contained within the cell was identical? If so, which traits would differ specifically? $\endgroup$– arnabanimeshFeb 18, 2015 at 15:01
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1$\begingroup$ No, playing with the zygote will not do it. It needs to be the nuclear material of the individual you want to clone inserted into a donor egg after it's nuclear material is removed. When one starts dividing, the embryo can be transplanted into a surrogate mother. Read about Dolly the sheep. $\endgroup$– anongoodnurseFeb 19, 2015 at 0:04
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$\begingroup$ Yeah, are you asking about strange cloning variation? $\endgroup$– MithoronFeb 21, 2015 at 1:12
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2 Answers
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The answer is no, and it is because sequence of the genome is not all information that is required for gene expression and development, there are also epigenetic factors.
A lot of patterns of epigenetic marks, such as most of DNA methylation and some histone modification patterns, are set during parental germline development, and these marks are transmitted to the zygote by gamets (except paternal histones, those are not transmitted because they are temporarily substituted for protamines in sperm for greater compaction). Therefore, the naked DNA inserted into zygotic nucleus will not have access to the machinery that established epigenome during development of the gametes.
And even though nucleosomes may assemble in the zygote on the naked DNA and histones may acquire post-translational modifications, and cytosines may get methylated, but most definitely the zygote is going to have no means to correctly set distinct patterns of epigenetic marks at alleles that are normally imprinted, i.e. those alleles whose epigenetic state depends on the gender of the organism that produced the gamete.
Therefore, the twin created in this way will have the same DNA sequence, but it will be a subject to disorders associated with imprinting
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$\begingroup$ If the epigenetic state of the alleles depends only on the gender of the organism producing the gamete, then it won't matter, or rather should it? $\endgroup$ Feb 21, 2015 at 5:47
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$\begingroup$ Majority of genes in gametes have similar epigenetic marks irrespective of the gender that produced them. However a small number of genes are modified differently in female gametogenesis in comparison to the male gametogenesis (i.e. the sexually imprinted genes). And I don't think that there is a way for such differential pattern to be established correctly in the zygote in your hypothetical experiment. $\endgroup$– SergeiFeb 21, 2015 at 11:07
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$\begingroup$ From your answer and comment, I am assuming that the epigenetic marks are the same for a gender (of a particular species, just for safety an extra assumption). And, for a cell to avoid disorders associated with imprinting it should have the same epigenetic markers, before it can undergo successful cloning process. So, if an in-vitro fertilization is done of two healthy gametes each from a male and a female humans. It should have the same epigenetic markers as any other fertilized human egg. Because here, as you say, in case of epigenetic markers, only the gender matters, not the individual. $\endgroup$ Feb 22, 2015 at 11:26
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DNA duplication (imagine, we PCR it) will net be enough. First of all, you also will have to duplicate and pack mitochondrial DNA into the cell. next, as been mentioned, epigenetic modification (methylation) and histone packing are crucial for proper development. And these markers should essentially replicate state of the host cell. My best guess is that all-synthetic replication atomic-resolution of zygote will be enough, but not just bare DNA code (750MB of information)
answered Feb 21, 2015 at 1:21
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$\begingroup$ Mitochondrial DNA is also a DNA. Apart from that, the mother could be kept the same, if that becomes a major hurdle. $\endgroup$ Feb 21, 2015 at 5:37