सीतानाथ समारम्भां रामानन्दार्य मध्यमाम्।
अस्मदाचार्य पर्यन्तां वन्दे श्रीगुरू परम्पराम् ।।
Very great question you have asked !!
See, their is a very common saying, “As Father As Son".
What ever be the appearance of a father around same will be the appearance of a son (avoid genetic variations). Means, if father have 1 face, 2 hands and 2 feet than son will also have same phenotypic appearance. If a father have just double of above mentioned than his son will also follow the same.
According to Vedās