Welcome back to the blog! Previously, some spicy Middle Ages drama was discussed along with the mammalian (humans included) sex-determination system with which most are familiar. “But what about other animals, though?” Glad you asked! Without further ado, let’s jump right on into it! Note: this post is already lengthy enough as it is, so it will only cover some of the major systems at play here.
Perhaps one of the most interesting cases is exhibited in reptiles, chiefly alligators and some turtles. After eggs are laid, at a critical time, or stage in development, sex will be determined by an external environmental (not gene-related) factor – temperature (see the right-side figure)! Imagine if humans were like this…I wonder if FL would be scary. As an aside, turtles make great pets if you’re like me – devoid of all emotion. Just kidding – they really bring low risk, medium reward to those seeking long, long-term companionship!
Next up is the tropical clownfish, a sequential hermaphrodite. A hermaphrodite is defined as an organism that has both male and female reproductive capabilities. Here comes the “sequential” part…all of them begin life as a male but will gradually switch teams to side with the females! Ew, traitors! If the alpha female goes bye-bye, then the leading male next in line will take over to mate with its following male. Simple, right? Needless to say, this would also be weird in humans. And I know what you’re wondering: “okay, but what about Marlin from Finding Nemo“. Yes, Nemo’s mother, the dominant female is gone, and there are no males more dominant than Marlin, so there’s no denying that it’s undoubtedly true! All of it! 100%. Perhaps one of your favorite childhood memories is now ruined, tainted forever. I speak the truth and you have been enlightened if you have read things that you cannot unread. You’re welcome. It’s okay, I know how you feel, my parents didn’t tell me either :(, but don’t worry, you’ll recover from this. No regrets. Moving on…
Finally, since I started this blog with my chicken stories, it’ll end where it all began. The chicken situation is a variation on the mammalian theme, or maybe it’s actually the other way around, who knows! Oh, the joys of scientific inquiry, right? Regardless, this time, the chick’s (not slang) sex is determined by the mother. The sex chromosomes are Z and W; males are ZZ while females are ZW. With this reversal of the mammalian system, there is still a 50/50 chance for either male/female, but sex is already predetermined prior to fertilization of the egg! Watch a video summary for more info here.
By the way, speaking of chromosomes, here’s a fun fact to satisfy the curious – chickens have 78 chromosomes, or 39 pairs, as opposed to humans’ 46 chromosomes, or 23 pairs! Although chickens have more chromosomes by the numbers, it does not necessarily mean anything in terms of intelligence or complexity. In fact, humans have a similar amount of genes and nucleotide base pairs (genome size) as many other animals. The chromosome count of an organism does not have much bearing, correlation, or weight over the intelligence/complexity nor does it necessarily have any observable, direct effect on the organism’s gene count or genome size. It is simply a figure that indicates how that species internally organizes its genes. What distinguishes humans from the rest, then? Have other organisms simply not reached their full, true potential? Why? More questions breed more answers. I’ll save the trouble of writing about gene regulation by saying “that’s a topic for…probably never”, but feel free to ponder or research if you don’t already know and are still wondering. Thankfully, this is where that conversation ends, phew. What’s next, “which came first, the chicken or the egg”?!
There are also other reproductive oddities and animal societies! Consider the monotremes (egg-laying mammals like the platypus or echidna), plants, lactating pigeons, “stabby” snails (look away children), wolbachia inhabited mosquitoes, fatherless bee/ant hierarchies, praying mantis mating, and the exclusively parthenogenetic (reproduction without any fertilization), all-female (major loss for the males I guess) New Mexico whiptail species (personally I prefer to refer to them as the sorority lizards because it just sounds cooler) among others; unfortunately, this post is nearing its end.
Human chromosomes are as dense as a tennis ball packed with 40 kilometers of string. Even with so much genetic information, somehow, the body simply knows what to do with it all to make us who we are, so let’s appreciate life a little more! I hope that you enjoyed reading and learned something new! I likely will not post here again for a very long time. Thank you to all of my readers – take care.
This was really interesting to read! I had no idea human chromosomes can be compared to the density of a tennis ball packed with 40 km of string. Also intriguing that chicken chromosomes do not correlate with intelligence or complexity regardless of the amount they have.
This was a really fascinating post! I had previously heard about some of the systems that you discussed (for instance, reptile sex determination being temperature-dependent), but I had a very surface level understanding of them. For that reason, it was interesting to learn more about them, such as with the charts of the specific patterns for reptiles that you included. I also thought it was cool to hear about chicken genetics; it’s really fascinating that their system is essentially the opposite of the mammalian one. I also had no idea that they had so many chromosomes. Moreover, I appreciated the nod to Wolbachia and mosquitoes, and the baby turtle picture is super cute! Excellent post!
I loved this a lot! I am actually going to miss responding to your blogs 🙁 But females are the better sex, no question about it. I am deeply traumatized now knowing the truth about Nemo however. It is so interesting how different species have different way of determining sex and how crucial it is to their survival. The only biology class I took is AP Bio in high school, but I plan to take a few more because I find them fascinating. Also, it is so cool that you helped hatch a turtle!!! My mom helped me raise and hatch butterflies when I was a kid, and it inspired a lot of passion for science. Well done!