A Mendelian trait in humans is how long you sleep in. Someone who wakes up early would have the (S) gene and someone who wakes up at a normal time would have the (s) gene. Someone waking up early would have either SS or Ss genes but someone who wakes up at a normal time would have the recessive gene ss. Something really cool about this is that since waking up early is a dominant gene you would think that 75% of people wake up early but its actually around 50% which is pretty cool.