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Sorry if you see me silly. I am just a programmer happens to be curious about biology...

So far I understand how DNA make protein, how cell divides, how one composed of cells->tissues-> organs.

But, still a piece is missing in my knowledge.. Given the sperm entering the egg creating the first cell, and the nutrients from the mother... how do that very first single cell diversify , multiply, transform to a human of many different type of cells, tissue and organs ? Is this all the diversification and specialization of cells directed just by the "child" DNA alone ?

Also, how does DNA (along with living condition ?) decide the course of my life (making me 1m tall at 6 y.o , have my hair black, my life expectancy etc..)

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    $\begingroup$ I think the cyclin proteins ( en.wikipedia.org/wiki/Cyclin ) control the cell cycle, of which a part of is cell division. And I think the mothers DNA are used for the "embryogenesis" up until a certain point, and then the child's DNA is used. ( en.wikipedia.org/wiki/Embryogenesis#Formation_of_the_gastrula ). I think this image gives a nice summary. ( upload.wikimedia.org/wikipedia/commons/8/8f/… ) . Sorry for giving a long comment instead of an answer, but i lack confidence in my biology. $\endgroup$
    – Ro Siv
    Commented Nov 27, 2015 at 21:06
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    $\begingroup$ Your question is a good one, but is unfortunately too broad for this forum as it encompasses the entire field of Developmental Biology. If you can narrow the focus of your question and ask a more specific question, then it is possible to get a good answer here. $\endgroup$
    – AMR
    Commented Nov 28, 2015 at 0:38
  • $\begingroup$ @AMR curiously, was there anything wrong with my line of thinking for my comment on this question? I feel I have been missing the mark for responses I give either due to my lack of experience or maybe general oversight. $\endgroup$
    – Ro Siv
    Commented Nov 28, 2015 at 2:27
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    $\begingroup$ @RoSiv Cyclins control the transitions from G1 through Mitosis/Meiosis, in any eukaryotic cell, throughout the organism's life, not just during dev. Your second sentence, has been shown fly development, though it is maternal mRNAs that are expressed before the embryo's. It has been shown in mouse eggs and it is possible that it occurs in human as well. Unlike fly development though, each duplication is marked with cell division. Flies go through several genomic divisions before they form distinct cells. $\endgroup$
    – AMR
    Commented Nov 28, 2015 at 3:47
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    $\begingroup$ @RoSiv The point of my comment wasn't really about your comment, it is that human embryogenesis is extremely complex and no able to be fit in this forum. There are Master Regulators, Body Plan Genes, Signaling from the uterus, Quorum sensing, different stages of cell differentiation from different cell lineages, just to name a few... Timing also plays an extremely important role. Many of our genes are nearly identical to most mammals, but it is when and how much those genes are expressed that is the main reason that we have evolved into Humans and our other cousins are other species. $\endgroup$
    – AMR
    Commented Nov 28, 2015 at 3:51

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The short answer is: "Nobody knows yet." The slightly longer answer is that different species use different mechanisms. In amphibians and insect the oocyte, or egg, produced by the mother, has a polarity such that some macromolecules are enriched in different regions of the egg. The best characterized examples are localized RNAs, but there could be other signals as well. In nematodes the site of sperm entry at fertilization determines the polarity of the cells, which then leads to asymmetry, etc.

In mice, our closest approximation to humans, the early cells after fertilization all seem equivalent, but as the number of cells increases the cells on the inside of the ball and the cells on the outside start to choose different differentiation pathways. There can also be signals from the extraembryonic environment (i.e., the womb).

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  • $\begingroup$ thanks! I hope it wont take too long for biologists/scientists to figure it out... $\endgroup$ Commented Nov 28, 2015 at 8:05

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