Part 1: Mechanism
Does bee relatedness make your head spin? Do you keep telling yourself that you should be able to do this because you have a biology degree? Do you have to teach undergraduates tomorrow? If any apply, then this blog post is for you.
Bee relatedness often baffles those of us with diploid brains. We see their relationships as exceptions, rather than results of rules. This post will explain why bees are related in seemingly strange ways.
Bees, along with the rest of Hymenoptera, have haplodiploid sex determination. The males are haploid and the females are diploid. Emphasize that the ploidy determines the sex, the same way that having an X and a Y chromosome determines a human is male.
2. Crossing Over/ Recombination
When a female produces gametes she does so the same way diploid organisms do. Crossing over occurs when her eggs are formed during prophase 1 of meiosis. Her unfertilized eggs are haploid. The genes of these eggs are not just one set of the female’s chromosomes but a product of genetic recombination of her two sets of chromosomes. The female is giving a randomized 50 percent of her genome.
Male bees produce sperm with their entire genome, as they are already haploid. All the sperm from an individual male bee are (ignoring mutations) identical to each other and to the male producing them.
A daughter is produced from a fertilized egg, which contains a recombined 50 percent of the maternal genome and 100 percent of the paternal genome.
A male is produced from an unfertilized egg. This egg is still produced by meiosis of the diploid mother’s chromosomes; this means that it is a recombined 50 percent of the maternal genome.
3. Recombination Drives Relatedness
The mother is 50 percent or 0.5 related to her sons, because she gave each son half of her genome. Her sons are 100 percent or 1.0 related to her, because each son’s entire genome came from her. Imagine a venture capitalist gives half her money to a company for a 100 percent equity stake. Her net wealth is only half determined by that company, but that company is entirely owned by her.
Additionally, male bees do not have fathers, nor do they have sons. Pedigrees typically show the male bee as the father for the sons of the female, but this is inaccurate. I recommend redrawing the pedigree, or at least erasing that line. White boards are useful in this regard. You may alternatively draw a separate line emanating from the female. Check back for Part Two: Pedigrees.