In some eusocial species such as honey bees sex determinatio

In some eusocial species, such as honey bees, sex determination occurs via haplodiploidy. As shown in the diagram, male drones develop from unfertilized eggs and are haploid, while queens and female workers develop from fertilized eggs and are diploid. Workers don\'t produce any offspring of their own, they instead help out in the hive, raising the queen\'s offspring, collecting pollen and nectar, and defending the hive. a) Assuming all the bees in a hive come from one male/female pair, what is the coefficient of relatedness (r) between the female workers in a hive? b) Why does this unique sex determination system make it more likely for altruistic behavior to occur than in a normal, entirely diploid species?

Solution

Coefficient of relationship (r) is a measure of the number of genes that two individuals have in common as a result of their genetic relationship.

i. The female workers are diploid; all of them would have inherited one set of genes (i.e. 50% of genes of worker) from the haploid drone.

ii. Similarly, the other set of genes (i.e. 50% of genes of worker) comes from the diploid queen, and the chances that the genes are identical between two workers is half (i.e. 50% of 50%) = 25%.

a. Hence, the number of genes that two sister workers have in common as a result of their genetic relationship = 50% + 25% = 75%

b. As shown above, two workers in a hive are related to each other by 75%. On the contrary (as shown in i) of they will be related to their progeny by 50%. Hence, the workers are more related to their sisters than their own progeny, making altruistic behavior more likely.