If a person is born either in Ashvini, Revati, Magha, Ashlesha, Moola or Jyeshtha nakshatra then the birth chart of the person is said to have Gandmool Dosha in the Jyotisha of so called pandits.
There are three points in the ecliptic at which the boundaries of two zodiac signs or rashis & the boundaries of two constellations or nakshatras coincide. If the moon is close to any of such three points at the time of birth of a person than the person is said to have Gandmool Dosha.
The first point is the boundary of the sign Aries (or Maish rashi) & the sign Taurus (or Vrish rashi) at which the boundary of Ashvini & Revati nakshatra also coincides.
The second point is the boundary of the sign Cancer (or Kark rashi) & the sign Leo (or Singh rashi) at which the boundary of Magha & Ashlesha nakshatra also coincides.
The third point is the boundary of the sign Scorpio (or Vrishchik rashi) & the sign Sagittarius (or Dhanu rashi) at which the boundary of Moola & Jyeshtha nakshatra also coincides.
If the birth chart of a child is said to contain such a dosha then it is said by the so called pandits that his father should not see the face of that child for the next 28 days after the birth of that child & a pooja should get done by the pandits in the interval of those 28 days.
But in actual such a dosha is a myth & has got a lot of exceptions because nothing bad happened to the fathers of such children who saw their faces with in 28 days of their birth, when no pooja was done by any of the pandits.
In actual, relationship with father is observed by analysing tenth house in the birth chart. Such a dosha is not a part of Indian Vedic Astrology & is a mere superstition.