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Suppose S is a dominant gene of dark skin and s is a recessive gene for light skin

Given two parents both with Ss genotype, the possible genotypes of their offspring are:

Ss x Ss = SS, Ss, Ss, ss

The Genotypic Ratio is: 1:2:1
The Phenotypic Ratio is: 3:1

Ang genotypic ratio ay kung anong klaseng mga genotype ang makukuha nila.
Sa phenotypic ratio ay kung anong characteristic ang actual na ma-oobserve.

So sa example, kunwari may apat silang anak na tig-iisa ng genotype na lumabas. Si Anak1 ay merong SS genotype, sina Anak2 at Anak3 ay may Ss genotype, at si Anak4 ay may ss genotype. Kaya 1:2:1 ang ratio. Kumbaga ito ang mga genes na meron sila.

Ngayon sa phenotype mo naman malalaman kung ano ang itsura nila. Dahil dominant gene ang dark skin, lahat ng anak na may S genotype ay may dark skin. So, sina Anak1(SS), Anak2(Ss) at Anak3(Ss) ay may dark skin, at si Anak4(ss) naman ay may light skin. Kaya 3:1 ang ratio, 3maitim:1maputi.