Here’s a riddle: Male honeybees don’t
have fathers, but they do have grandfathers. They also can’t have sons,
but they can have grandsons. How is this possible?
Bees have weird family trees because of something called haplodiploidy.
Ploidy refers to the number of chromosome copies an organism has. Humans are
diploid; we have one set of 23 chromosomes from our mothers and one set from our fathers. Honeybee queens and female workers are also diploid, with two
sets of 16 chromosomes. But the male drones are haploid and have just one set
that they inherit from their mother, a queen, when she lays an unfertilized egg.
This difference makes for an interesting family tree. Let’s say the black bar is a
drone’s chromosomes. When he mates with a queen, with the yellow chromosomes, his
daughters will get his black chromosomes. Their brothers, however, will not. These
daughter queens will eventually mate and lay their own eggs. Their sons may end up
with their yellow chromosome or they may get their grandfather’s black chromosome.
So take a moment to appreciate the weird bee family tree, just not on Father’s Day.
For Scientific American, I’m Tim Palmieri.