If you know a little about basic biology, I bet you know that most women have two x
chromosomes and most men have an x and y.
But do you know some females have a W chromosome?
Hey science fans, Julia here for DNews
Bird sex is a little weird.
No I don’t mean because everything happens with one hole..
I mean like male/female kind of sex.
I mean…
Bird’s have strange chromosomes.
Let’s start off with what we know of our sex chromosomes.
Most women carry two x chromosomes and most men carry an x AND a y.
There’s room for variation of course, some people have more than one x, like XXY or xxx.
And this is true for a lot of organisms, like humans and cats and mice and things.
In these cases the female organisms produce one type of gamete, all X. but males produce
two types, x and y.
It’s the male gamete, or sperm that decides the sex of the offspring.
But in reptiles it works a little differently.
It’s not necessarily the gametes that determine sex but the temperature.
Like take the American Alligator for example, both high and low temperatures turn the eggs
female while middle range temperatures make the eggs male.
A reptilian ancestor of both humans and birds probably relied on this system.
But give or take a few million years and something else entirely emerged.
Birds have ZW chromosomes.
Yeah you heard that right, ZW.
Which stands for Zery Weird.
Okay not really.
But the ZW chromosomes look nothing like the XY ones, they don’t share any genes!
But they are kind of similar in that the W chromosome is shrunken, just like Y is in
our genome.
but wait.
it gets weirder.
In birds, MALES are the homomorphic sex, mean they are the ones with the double zzs.
where the females are heteromorphic and have their own chromosome.
They get both the z and w chromosomes.
But interestingly, in a recent study published the journal Nature Communications found that
the W chromosome does not have the genes that lead to the development of the female.
But the researchers think that the W is a buffer and that the organisms need two copies
of certain genes to survive.
According to another study published in the journal Science Progress, the Z chromosome
is large and contains almost all the known sex-linked genes.
So it’s the presence of the number of Z chromosomes that change the sex of the offspring.
Two copies of it produces a male, one copy (plus a W chromosome) produces a female.
But why did they evolve this way?
Researchers think that sex chromosomes evolved from autosomes.
And the split between ZW and XY systems happened once a long time ago, since they don’t share
any genes.
Maybe birds got this flip-flopped gene set up because of sexual selection.
Many species of birds have males with extreme characteristics.
Think of like a peacock.
That big tail might garner some womanly affection, but it doesn’t enable him to fly.
If a female were to get these traits, maybe it would be detrimental, so having another
chromosome might balance out some of those traits.
And having these sex related traits on the Z chromosome means that when a male gets DOUBLE
those traits he’s like EXTRA masculine.
But that’s just a theory, scientists aren’t exactly sure.
So I guess you might say…
more research is needed!
But weirdly other organisms have similar ZW systems, but the W chromosome does determine
the females.
Some Lepidoptera - moths and butterflies have Z0, ZZW, and ZZWW genotypes.
yeah, the world of animal sex is just weird.
Speaking of butterflies, have you ever wondered what happens inside of a cocoon?
Check out this great episode from my brand new show
TestTube 101.