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Our body contains many different types of cells and each of those cells have their own DNA (correct me if wrong) like skin cells their own DNA that makes them skin cells instead of muscle cells.

So my question is what DNA does a human pass down in a sperm or egg cell? Is it a specialised DNA imprint from which our whole body can be created?

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    $\begingroup$ Nope, you are incorrect here. Everey cell carries a complete set of genomic information, it is "only" differently expressed (read out). The only exception are egg and sperm cells, which carry only half a set of chromosomes (23 instead of 46) to be able to combine with their counterpart. $\endgroup$ – Chris Feb 6 '16 at 13:14
  • $\begingroup$ In giving birth, the sex cells join to form a zygote of 23+23 = 46 chromosomes. This zygote contains both the chromosomes. These chromosomes affect a variety of things like gender etc $\endgroup$ – Tusky Feb 6 '16 at 14:13
  • $\begingroup$ Only cells in the germ line are used to produce sperm and eggs, which are passed to offspring. DNA in all other cells (somatic cells) are not passed to offspring. $\endgroup$ – fileunderwater Feb 6 '16 at 20:00
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Most cells in a human body contain a complete set of the genome, which is two sets of 23 chromosomes. Having two of each chromosome is called diploidy.

Within an individual human the DNA is approximately identical in every cell. Different cells are produced by differential use of that DNA: certain genes are more (or less) highly expressed etc. You can read more about that here.

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You inherit one copy of each chromosome from each parent. Gametes (eggs and sperm) are a bit different from regular cells because they contain one copy of each chromosome; they are haploid. These gametes fuse to make the complete set of 23 pairs in the offspring. There are some exceptions such as cytoplasmic DNA and sex chromosomes.

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  • $\begingroup$ Good answer +1. You might want to indicate the following posts that will answer these questions: Why is there protein variation between cells without much genetic variation?, Do both parents really contribute equally? and Do our gene change as we age?. $\endgroup$ – Remi.b Feb 6 '16 at 19:20
  • $\begingroup$ For clarity (and due to misconceptions in the question), I think you should specifically mention germline cells (in contrast to somatic cells), and how only cells in the germline are used for reproduction. $\endgroup$ – fileunderwater Feb 6 '16 at 20:03
  • $\begingroup$ I think you should also clarify that it's not actually the parent's chromosomes that are being passed on (looks like that in the figure), but rather a mosaic of their chromosomes, due to meiosis / crossing over. $\endgroup$ – Roland Feb 7 '16 at 0:28
  • $\begingroup$ so in a nutshell you can create a full body clone of a person from just about any type of cell's DNA ? $\endgroup$ – user1062760 Feb 7 '16 at 16:51
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    $\begingroup$ @user1062760 Well, you can't make a clone of a person from any type of cell -- that's not been done, it's not known how, and it isn't allowed, at least in Western countries. But the concept is correct; mice can be cloned from skin cells, for example (pnas.org/content/104/8/2738.full). $\endgroup$ – iayork Feb 9 '16 at 13:40
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Genetics is an evolving field : ) Concepts such as Horizontal Gene Transfer are important, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5379729/ Also the boundaries of the “body” may be considered, e.g. Obviously the DNA sequences of gut flora are distinct from the statistically major portion of DNA of human somatic cells, but are gut flora not an integral part of the body? Sorry to answer a question with a question but such is the nature of philosophy. Another concept worth noting is microchimerism, a striking example of which is seen in the maintenance in females of a small sub population of cells in the brain and other organs that contain the DNA of former sexual partners; pregnancy specifically, often results in horizontal gene transfer with clear effects https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3458919/

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Ideally, DNA itself is the same in DNA-containing cell types. Cell type depends on expression, which depends on epigenetics. I.e. histone modification, DNA methylation, and few other mechanisms.

Also, epigenetics is the mechanism for gene expression regulation. For example, it can silence (usually, methylate promoter regions) an expression of genes on one of the chromosomes in female cells. It's called genomic imprinting. In mammals epigenetics tags from gametes are not stripped after zygote formation.

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    $\begingroup$ Epigenetics is not only the mechanism to silence one chromosome in cats. It is the mechanism by which genes (and chromosomes) can be regulated by special enzymes. The regulation includes activation and silencing. $\endgroup$ – Chris Feb 11 '16 at 19:20
  • $\begingroup$ And DNA is not the same in each cell type; think gametes vs somatic cells, random mutations and cells without DNA (RBCs). This answer needs to be toned down. $\endgroup$ – AliceD Feb 11 '16 at 19:50
  • $\begingroup$ So the removal of half the chromosomes from both parent cells happens as the zygote is formed and not before zygote formation right? otherwise you'd have a fixed set of chromosomes that are removed from each parent cell for entire species $\endgroup$ – user1062760 Feb 11 '16 at 20:04
  • $\begingroup$ @user1062760 a sperm and ovum are haploid cells so they have a single set of chromosomes. However an ovum becomes haploid in an oogenesis process so in the very beginning it was a diploid oogonum. $\endgroup$ – Maxim Kuleshov Feb 11 '16 at 20:57
  • $\begingroup$ I agree with Chris. There are examples in which the gene network is capable of showing multiple types of stable responses (for two kinds this is known as bistability). Positive feedbacks, for instance, can show bistability without the involvement of additional epigenetic regulation. However, as you said epigenetic modification are essential for maintaining the differentiated lineage (a sort of memory which can be inherited). So, it would be great if you can improve your answer and also add some references. $\endgroup$ – WYSIWYG Feb 12 '16 at 10:26
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Mitochondrial DNA is inherited mostly from the female line and is derived mostly from the ova. Mitochondria are present in all cells but retain genomes that are distinct from the host organism’s DNA, almost as if they are a separate single called organism. Here is an interesting look at mitochondrial DNA https://www.ncbi.nlm.nih.gov/pmc/articles/PMC19448/#!po=0.943396

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