Beti maa pe jaati hai beta baap pe jaata hai, Budh lagan ka ho toh yahi samajh aata hai.
The daughter takes after the mother, the son takes after the father; if Mercury is in the Ascendant, this is what is understood.
Mercury (Budh) is the planet of copying, mimicking, and communication. The 1st house (Lagan) represents the physical body and the core personality.
When Mercury sits in the 1st house, it acts like a perfect genetic mirror. Dr. Sharma explains a very specific Lal Kitab rule regarding the children of this person.
If a person has Mercury in the 1st house, their children will be exact copies of their respective genders. The daughter will look and act exactly like the mother ("beti maa pe jaati hai"), and the son will be an exact replica of the father ("beta baap pe jaata hai"). Mercury simply duplicates the DNA perfectly.