In human reproduction the male produces sperm containing 23 chromosomes and the female has the oovum containing 23 chromosomes , so after fertilization the zygote contains 46 chromosomes. What I want to know is , how do the chromosomes identify each other and pair up, fir example say ,how does chromosome '1' of the male pair up with chromosome '1' of the female to make set '1' of the zygote?

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    $\begingroup$ I don't understand your question. 23 chromosomes from the mother, 23 from the father and they combined in 23 pairs of chromosomes. What exactly is unclear to you? Maybe you'll want to watch an introductory class about genetics such as e.g. the series of lectures from Khan Academy $\endgroup$ – Remi.b Jul 27 '18 at 19:15
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    $\begingroup$ Do want to know, how for example the male and female chromosome 1 "find" each other and pair up in the zygote? $\endgroup$ – Arsak Jul 27 '18 at 21:03
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    $\begingroup$ Yes that 's right , what I am asking is that after fertilisation how do the chromosomes find each other and pair up. $\endgroup$ – user45134 Jul 28 '18 at 12:18

After fertilization the diploid cells divide by mitosis. Chromosomes don’t need to pair with their partner during the eukaryotic cell cycle. After S-phase each chromosome has been duplicated (so there are 46 + 46 = 92). The two daughter chromosomes resulting from semi-conservative DNA replication are held together at one point: their centromeres. In M-phase two microtubules from opposite poles of the mitotic spindle will attach to the kinetochore that assembles at those centromeres.

Nowhere in this process is the maternal chr1 required to interact with the paternal chr1.

The pairing that you are refering to takes place much later after the new primordial germ cells haved developed into the germline, leading to meiosis. The molecular details of homolog pairing during meiosis are best understood in the model organism C. elegans where each chromosome has specific cis-acting sequences that are recognized by different trans-acting factors that lead to recognition and then pairing, followed by synapsis, and eventually crossing over.

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