The following is the hadith which explains why baby resembles with one of the parents:
Imam Muslim narrated in his Sahih from Anas ibn Malik:
Umm Sulaym [Anas' mother] said that she once asked the Prophet about a woman that sees, upon waking up, [traces of an emission of fluid] just as a man can. The Prophet MHMD replied, "When a woman sees this, let her wash from head to toe." Umm Sulaym said that she felt shy to ask such a thing and added, "Can such a thing truly take place?" The Godsent Prophet said MHMD - upon him blessings and peace: "Yes, it can. Where else does [parental] resemblance originate [in the child]? Indeed, the fluid of the man is thick and white while the fluid of the woman is thin and yellow. Whichever of the two surpasses (`ala) or precedes (sabaqa) the other, dictates resemblance."
Although in other hadiths where fluid of woman is mentioned the scholars have interpreted it to mean chromosomes,genetics,gametes.
But the above hadith makes it otherwise which proves to the reader that Prophet (PBUH) was talking about physical fluid which apparently has nothing to do with the fertilization in anyway. Someone tried to refute it by mentioning the "Courpus lieutium" a yellow body filled with yellowish fluid but that fluid doesn't come out of vagina. Or in other words vaginal discharge is something different. So any ideas regarding this?