What do March 21st and September 21st have in common?

The equinoxes are the only time when both the Northern and Southern Hemispheres experience roughly equal amounts of daytime and nighttime. On Earth, there are two equinoxes every year: one around March 21 and another around September 22.

Explanation:

uranium-238 i believe is your answer

the child will have heterozygous dominant chromosomes as characters of his father are dominant over the characters of his mother.

the child is heterozygous