A few of the facts that biology teacher Grace Pokela shares:
sex chromosomal variety: Insects use an XO sex determination system, while birds use the ZW system.
environmental factors for sex: A reptile’s sex is at least partly determined by the temperature in which the egg develops.
hermaphroditism: Flatworms transfer sperm through a process called penis fencing (which is described in graphic detail here).
hermaphroditism & sex change: In clownfish colonies, dominance is based on size, the female being the largest and the male being the second largest. If the female dies, the male gains weight and becomes the female for that group.
Editor’s note: The term "hermaphrodite" is appropriate for referring to non-human animals with sex characteristics that do not fit typical binary notions of male or female bodies. For humans, “intersex” is the appropriate term—learn more here!
transgender behavior: Other fish species take on female attributes while mating, and they release sperm in the process.
2+ sexes: Fungi like molds and mushrooms have 36,000 sexes.
In humans, 5-alpha-reductase deficiency is a real (albeit rare) condition, in which young women grow a penis during puberty.
In humans, androgen insensitivity syndrome (AHS) is an intersex condition in which a person who is genetically male is resistant to male hormones . As a result, the person has some or all of the physical traits of a woman, but the genetic makeup of a man.
In humans, the SRY gene is involved in male sexual development—without it fetuses can be genetically male (with XY chromosomes) but have a female body. The same is true in females (with XX chromosomes), who can develop a male body without the SRY gene.
In humans, XXY males are sterile, with small testes—while women with only one X chromosome (a condition called Turner syndrome) are infertile and don’t go through puberty. Males with two X chromosomes (called Klinefelter syndrome) are taller, with a higher risk of breast cancer and osteoporosis.
Read more at https://observer.com/2017/03/transgender-facebook-troll-biology-sexuality/