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I am not well-versed in biology so this question might be wrong. As far as I understand meiosis, two germ line cells with 23 chromosomes each (one cell from the father and another from the mother) combine and after meiosis we get recombined chromosomes from the haploid cells with 23 chromosomes that will develop into an embryo. So, the child has different chromosomes than the ones of his father and mother. Then how can we know, by analyzing the child's DNA, who are the parents?

My simple question comes, in part, from this video about meiosis

I apologize for any errors.

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Your description is not totally correct (or understandable). There is plenty of source of information online so, I won't repeat the whole thing here. In very short and very simplified, talking about humans...

Ploidy, meiosis and fecundation

Both parents are diploid (2N=46). Both parents have specific cells that are undergoing meiosis (in testis and in ovaries). After meiosis, the cells (spermatozoids and ovules) are haploid (1N = 23). The spermatozoid and the ovule fuse (fecundation) to make another diploid (2N = 46) individual. This diploid individual will grow for about 9 months in the mother's uterus before coming out!

Crossover

Now, during meiosis, cross-over occurs. It is a mechanism where the two chromosomes mix up their material. When the cross-over occurs in the father for example, it is the chromosome that the father receive from his father and the chromosome that he received from his mother that mix-up their genetic material.

Possible chromosomes

Let's say the maternally inherited chromosome of the dad is

AAAAAAAAAAAAAA

Let's say the paternally inherited chromosome of the dad is

BBBBBBBBBBBBBB

Then, in the meiosis (where spermatozoids are produced), the two chromosome might mix up and the haploid spermatzoid can end up with something like

BBBBBBBBBBBAAA

Now, on the mother's side, her two chromosomes are, say,

CCCCCCCCCCCCCC

and 

DDDDDDDDDDDDDD

The mother might therefore transmit

DDDDDDDCCCCCCC

The (diploid) baby would then be 

BBBBBBBBBBBAAA
DDDDDDDCCCCCCC

So of course, the chromosomes present in the baby are a bit different form the ones present in the parents but we can still recognize them. If there is doubt who the father is, a genetic analysis of another father might return the chromosomes

BBBBBBBBBBBBBB
FFFFFFFFFFFFFF

, then we would know this individual cannot be the father because he could have not transmitted the AAA part of the chromosome found in the kid.

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  • $\begingroup$ So their parents have the DNA very much like the son but not equal..that was the point in the question.. $\endgroup$ – user38033 Nov 12 '17 at 2:05
  • $\begingroup$ @santimirandarp I am not sure by your comment if you feel like the question has been answered. If not, can you please explain why? $\endgroup$ – Remi.b Nov 14 '17 at 18:57
  • $\begingroup$ I was waiting for another good answer. It was good. I will accept. $\endgroup$ – user38033 Nov 14 '17 at 20:32
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To solve this mystery or get the answer by a well known technology even to a lamen called DNA fingerprinting. This technique is applied to the DNA which is extracted from the parents and the child, then these will be analyzed simultaneously and the result would be like of they are really the child's parents the all 3 have many equality and if they are not then all 3 DNA are widely distinct.

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