Sex Determination: More Complicated Than You Thought

Sex Determination: More Complicated Than You Thought

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Translator: Bedirhan Cinar My wife is pregnant right
now with our first child, and when people see her
with her big baby bump, the first question people ask,
almost without fail, is, “Is it a boy or is it a girl?” Now, there are some assumptions
behind that question that we take for granted because of our familiarity
with our own human biology. For human babies, we take it for granted
that there’s a 50/50 chance of either answer, boy or girl. But why is it that way? Well, the answer depends
on the sex determination system that has evolved for our species. You see, for most mammals, the sex of a baby
is determined genetically with the XY chromosome system. Mammals have a pair of sex chromosomes, one passed down from mom,
and one from dad. A pair of X’s gives us a girl, and an X and a Y together gives us a boy. Since females only have X’s to pass
on in their egg cells, and males can give either an X
or a Y in their sperm cells, the sex is determined by the father and the chance of producing
a male or a female is 50/50. This system has worked well for mammals, but throughout the tree of life,
we can see other systems that have worked just
as well for other animals. There are other groups of animals
that also have genetic sex determination, but their systems can be
pretty different from ours. Birds and some reptiles have
their sex genetically determined, but instead of the sex
being determined by dad, their sex is determined by mom. In those groups,
a pair of Z sex chromosomes produces a male, so these males
only have Z’s to give. However, in these animals,
one Z and one W chromosome together, as a pair, produces a female. In this system, the chance of a male
or a female is still 50/50, it just depends on whether
mom puts a Z or a W into her egg. Certain groups have taken
genetic sex determination in completely other directions. Ants, for example, have
one of the most interesting systems for determining sex, and because of it,
if you are a male ant, you do not have a father. In an ant colony, there
are dramatic divisions of labor. There are soldiers that defend the colony, there are workers that collect food,
clean the nest and care for the young, and there’s a queen and a small group
of male reproductives. Now, the queen will mate and then
store sperm from the males. And this is where the system
gets really interesting. If the queen uses the stored
sperm to fertilize an egg, then that egg will grow up
to become female. However, if she lays an egg
without fertilizing it, then that egg will still
grow up to be an ant, but it will always be a male. So you see, it’s impossible
for male ants to have fathers. And male ants live their life like this,
with only one copy of every gene, much like a walking sex cell. This system is called
a haplodiploid system, and we see it not only in ants, but also in other highly social
insects like bees and wasps. Since our own sex is determined by genes, and we do know of these other animals
that have their sex determined by genes, it’s easy to assume that for all animals the sex of their babies still
must be determined by genetics. However, for some animals, the question
of whether it will be a boy or a girl has nothing to do with genes at all, and it can depend on something
like the weather. These are animals like alligators
and most turtles. In these animals, the sex
of an embryo in a developing egg is determined by the temperature. In these species, the sex of the baby is not yet determined
when the egg is laid, and it remains undetermined
until sometime in the middle of the overall development period,
when a critical time is reached. And during this time, the sex
is completely determined by temperature in the nest. In painted turtles, for example, warm temperatures
above the critical temperature will produce females within the eggs, and cool temperatures will produce a male. I’m not sure who came up
with this mnemonic, but you can remember that when
it comes to painted turtles, they are all hot chicks and cool dudes. For some tropical fish, the question
of will it be a boy or will it be a girl isn’t settled until even later in life. You see, clownfish all start
out their lives as males, However, as they mature,
they become female. They also spend their lives in small
groups with a strict dominance hierarchy where only the most dominant
male and female reproduce. And amazingly, if the dominant
female in the group dies, the largest and most dominant male
will then quickly become female and take her place,
and all of the other males will move up one rank in the hierarchy. In another very different ocean animal, the green spoonworm, the sex of the babies is determined by a completely different aspect
of the environment. For this species, it is simply
a matter of where a larva happens to randomly fall on the sea floor. If a larva lands on the open sea floor,
then it will become a female. But if it lands on top of a female,
then it will become a male. So for some species,
the question of boy or girl is answered by genetics. For others, it’s answered
by the environment. And for others still, they don’t even
bother with the question at all. Take whiptail lizards, for example. For those desert lizards,
the answer is easy. It’s a girl. It’s always a girl. They are a nearly all-female species,
and although they still lay eggs, these eggs hatch out
female clones of themselves. So will it be a girl or will it be a boy? Throughout the entire animal kingdom, it does really all depend
on the system of sex determination. For humans, that system
is a genetic XY system. And for me and my wife, we found out it’s going to be a baby boy. (Kiss)

100 thoughts on “Sex Determination: More Complicated Than You Thought”

  1. Turtle logic: hot chicks n cool dudes.

    : however made those words knew what they were doing

  2. Nemo was a baby without mother… But soon he will get his mother ?? because his daddy will become his mother

  3. Wait… Did anyone else notice we completely skipped over slugs and snails? It looks like from the graphic that they're intersex

  4. 3:14 Upper left corner
    -Snails are Hemafrodites, which means they personally have both sexes altrough during it they battle with a "Love Dart" to determine who should be a male and who should be a female, this is becauase depending on the species no snail or slug really wants to lay up to 300 eggs.
    -Look it up.

  5. BUt tHErE aRE 439384959392938585839292919919598585588483838292919192939495858588558483829292992299 GEndERs REEEEEE

  6. In the haplodiploid sysyem a male is half the queens DNA then she mates with a male meaning that its her own DNA right? Thats weird

  7. Isn’t more like approximately 50/50 and not actually 50/50? Ya know, cause of intersex people?
    ( they used to be called hermodromites, well I spelled that wrong, but you know what I meant, but now you are supposed to call them intersex kinda like how people used to call native Americans Indians but then that changed)

  8. Omg…
    I was living a lie till now… Due to nemo movie..
    I'm scared.. Disney is sometimes.. Okay, i cant explain..

  9. Complicated? Everything is only as complicated as someone makes it. Would you be a boy or girl? I don't care. Do what makes you happy. See! Everything is a simple as someone makes it.

  10. There goes quranic theory of everything exists in pairs or twos down the drain. Only higher animals exist in pairs. Quran is fantasy of Muhammad not words of Allah.

  11. It is very important always to mention about the intersex case in humans and how common it is. I'm really tired of listen to people saying that it is fake news, nonsense etc. . . with the intention of "to create an ideology which change the NATURAL gender social patterns" ? This 50 – 50 saying is more than not honest, it is very prejudicial ??‍♂️ People are born intersex and that is what they are sometimes even in the very well read DNA level. Their existence needs to be mentioned.

  12. Imagine if the Ant Queen's whole process of keeping the girl and kicking out the boy thing was in human version………that would just be so cruel.

  13. If you are a human the baby would be a girl inside of the belly but over time it would be something else or just a girl

  14. Lol, don't you know, that people may be not girl or boy? Even your genetic code not make you male or female always.

  15. Male Clown fish 1:Poor Rick his wife died..
    Male Clown fish 2:Ya…
    2 months later
    Male Clown fish 1 sees a female Clown fish
    Male Clown fish 1:Well hello beautiful! What’s you’re name?
    Female Clown fish:I’m Rick don’t I know you?
    Male Clown fish:AHHHHHHHHHHHHHHH

  16. Am I the only one that thought this was going to be one of those things where they tell you there are like 60 genders

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