 Quick question! Do you think you can determine the sex of an animal without sex chromosomes? Yes? No? Maybe? Well, yes, you can. In fact, the first sex determination system was reported 50 years before the discovery of sex chromosomes and that too in honeybees. It had all started with a Polish priest who also happened to be a beekeeper. One fine day he came across a queen bee that hadn't mated with any other bee and yet gave birth to perfectly healthy male bees. What? How is that even possible? This queen bee was a complete virgin. She had never ever mated with anyone and yet she had children? I mean, where's the father? Who's the father? Spoiler alert! They don't have any fathers, but they do have grandfathers. What? Now, all of this might be super confusing. So, let me walk you through the unique world of sex determination in honeybees. Now, before we go ahead and find out exactly how you can determine the sex of an honeybee, let me give you a quick rundown of how the bee community works or the different types of honeybees that you can see inside a bee hive. So, there are three types of honeybees that you're going to find inside a bee hive. You'll have the workers, the drones, and the queen herself. The workers are all female bees which take care of pretty much everything inside the bee hive. They are the ones who tend to the queen, they are the ones who take care of the young ones, they collect nectar from different flowers, they protect the bee hive, they in fact clean the bee hive too. Every sort of job that you can think of except for reproduction if all of those things are taken care of by the worker bees. Then we have the drones and all of the drones are males and their sole purpose in life is to go ahead and mate with the queen bee. That's it, that's all they are there for. And then finally we have our queen who reigns over the entire bee hive and her major purpose in life or the main purpose of her life is to maintain the bee population. So, whenever the time comes she goes ahead and mates with multiple drones and increases the bee population and maintains the entire number of bees inside the hive. Now things start to get a little weird when you look at the genomes of these bees. You see the females aka the workers and the queen bee they are diploid organisms like you and me meaning that they have two sets of chromosomes. On the other hand the males are haploid organisms meaning that they have only one set of chromosomes kind of like how our gametes or sex cells are. So if the drones have about 16 chromosomes then the females or the workers and the queen bee will have twice of those chromosomes so that would make about 32 chromosomes. Now these numbers don't really matter much. What is really important is the mating that takes place between this haploid male and the diploid female. So when the haploid male mates with the diploid female we are introduced to a system called the haplodeploid system or simply haplodeploidy. Now what exactly happens in haplodeploidy and how do you determine the sex? Let's find out. First off when the queen bee decides to mate she doesn't mate with one single drone. She always mates with multiple drones. In fact sometimes the numbers are as high as about 50 drones. So our queen bee she will go ahead and mate with 50 different drones. Now our queen also comes with very special powers. What she's going to do is she will collect all of the sperms that she gets from these drones and she's going to store them within a little pouch inside of her. So she collects all of those sperms and she keeps them with her. So when she finally decides to fertilize her eggs she's going to use this bag of sperms to fertilize those eggs. You heard me right. Our queen bee can choose whether she wants to fertilize her eggs or not. So this choice that the queen bee has this is what determines the sex of the honey bee. So let's say that our queen bee lays multiple eggs and she decides to fertilize some of her eggs. So there you go there you go. Now she uses the bag of sperms that she has and she has decided to fertilize her eggs. Now this fertilization will lead to the production of deployed female bees. So fertilized eggs will always hatch to give birth to deployed female bees. Now what exactly happens to the eggs which are not fertilized? Do they go to waste? Absolutely not. These eggs will also hatch but this time it won't go through the process of fertilization. Instead it will go through another process called parthenogenesis which means that these unfertilized eggs will hatch to give honey bees as well but these honey bees will always be male. Parthenogenesis is the process of the birth of young ones without fertilization and these male honey bees they are a product of parthenogenesis. Now these male bees will be haploid like we had seen earlier all the drones are haploid. So unfertilized eggs will give birth to haploid males while fertilized eggs will give birth to deployed female bees. Now the queen bee is not the only source of unfertilized eggs. Remember I said that all the worker bees are females and they do every single job except for reproduction? Well they do but that doesn't mean that they don't lay eggs because at the end of the day they're all female bees and they do lay eggs but they just don't have the power to fertilize those eggs. Hence all the eggs that the female worker bees lay also remain unfertilized so those eggs will always give birth to haploid male bees. So over here can you recall something that I had told you right at the beginning of this video? Remember how I said that honey bees don't have fathers but they have grandfathers? Well you can see it's impossible for them to have fathers because every male bee comes from their mothers and mothers only. These eggs are not fertilized in any way whatsoever so they don't have a father at all but that doesn't mean that they don't have any grandfathers. You see their mother is a product of a fertilized egg she's a female so she definitely has a dad and that means that her children has a granddad. So every male bee does not have a father but they definitely have a grandfather. Similarly these haploid males will always give birth like will always be a part of the fertilization process and they will end up becoming fathers to multiple female bees but never male bees. So these bees can never have sons but they can have grandsons because these haploid males are involved in the birth of the female bees which will go ahead and give birth to sons meaning that these haploid male bees can have grandsons but no sons of their own. Now the scientists were pretty happy with this conclusion all the fertilized eggs are giving female bees all the time and all the unfertilized eggs are giving male bees all the time. Now one fine day while the scientists were working and researching more with honeybees they came across something extremely unusual. They saw that some fertilized eggs hatched and gave rise to diploid male bees. Wait what? We just concluded that fertilized eggs always give us female bees. We're pretty sure about that and we have also concluded that that's how the sex is getting determined. Then where do these males come from? The scientists were as stumped as you and me. So what did they decide to do? They decided to research some more and that's when they realized one aspect of this entire sex determination system that they hadn't considered at all. You see just because honeybees don't have sex chromosomes doesn't mean that they don't have genes. The scientists were able to come across one particular gene called the complementary sex determiner gene and this gene decided the sexual fate of the honeybees. Now how exactly does that work? Now this is a huge name for a gene. Let's simply call it the A gene that will make things a lot easier for us to understand. So every honeybee has this complementary sex determiner gene or the A gene that we're calling it now. This when the scientists looked more into researching about the honeybees they found that there are over 120 copies of this A gene or there are more than 120 alleles of this A gene. So any bee, so all the female bees which are the diploids they can have any combination of two sets or two copies of this gene. I mean there are over 120 alleles of this gene. So you can imagine how many combinations you can come up with. The diversity is so huge and it is this diversity of alleles which was running the whole show of whether a honeybee gets to be a male or a female. Now how? Now this A gene this will come in two copies in the females and in one and it'll have there'll be only one copy in the males. So let us assume that this queen bee that we have over here. Let's say that she has two different copies of this A gene. So she has the copies A2 and A3. Now she has gone ahead and mated with multiple different drones. Now all of these drones can have a different copy altogether. So let's say one of them has A3, one of them has A4, one of them has A5. Okay now when the fertilization takes place and the females are born they are also diploids. So the females will receive one copy of this gene from the mom and one copy from their dad. Their dad has only one copy to give anyway. So when the scientists look more into it they realized that all the females received two different copies every single time. Meaning that all the fertilized eggs were giving birth to females and those females had two extremely different copies of the gene. So it was heterozygous at the A gene locus. So it was getting either an A2 from the mom and an A4 from the dad or an A3 from the mom and A5 from the dad. So these copies were always different. They were always heterozygous and it is this heterozygous combination which was deciding that the honey bee is going to be a female bee and not a male bee. So what happens in the case of the males? The males are unfertilized right? They don't have to get another set from anyone. So they will have one of the copies from the mom. So these eggs will have either A2 or the A3 gene that these genes that the mom had. So the haploid male will either have an A2 or an A3 gene that he can get only from the mom. Now since the males are haploid so they will have only one copy of the gene meaning that they are hemizygous at the A gene locus, hemi meaning half. So when it is hemizygous when it's a hemizygous not a combination but it's hemizygous at the gene locus then those bees will always be a male but when it is heterozygous those bees will always develop into a female. Now in the case of the diploid males these two copies were exactly the same. So instead of receiving two different copies they ended up receiving the same copy from both of its parents. So the dad also gave an A3 and the mom also gave an A3. So in these diploid males the combination of the alleles was homozygous at the A gene locus meaning that they were identical to one another and that is why they were diploid males. Deployed why? Because they have two sets of chromosomes and hence when we say that fertilized eggs always give birth to females it's actually wrong. They always don't. Sometimes they give birth to diploid males who never survive by the way. Now these diploid males have no job whatsoever in the bee community. So they are killed off at the larval stage itself. These bees don't survive at all and that is how the whole sex determination thing really works. Something that we didn't really have an idea about before but we do now.