[Lee Mac]

Lee Mac  asked the Naked Scientists:
   
Its said we all start out female.  Do all or most creatures start out this way ?

Thanks, Love to hear you[/url]


What do you think?

[Jolly- Joliver]

Lee Mac  asked the Naked Scientists:
   
Its said we all start out female.  Do all or most creatures start out this way ?

Thanks, Love to hear you[/url]


What do you think?

Not sure I cannot believe that there isnt an animal somewhere that does it another way, there's always one(not to say all life start out that way in the first place).

[lab monkey]

Have I missed something?  How do we all start out female?

We're derived from a single fertilised egg which already dictates your sex.  It's set at the point of fertilisation...

[Farcanal]

At conception we are both sexes (or no sexes) and it's not until the genes kick in after the first month in the womb that governs which gender we end up.

[imatfaal]

At conception we are both sexes (or no sexes) and it's not until the genes kick in after the first month in the womb that governs which gender we end up.

Sorry FarC - that's just not right.  Whilst there may not be obvious physical noticeable difference in the zygote/early embryo - our sex is determined upon conception.  To keep it very simple and for humans/mammals; some sperm carry a y sex-chromosome and others carry an x-sex chromosome, the ovum carries an x.  When combined after fertilization an x and a y leads to a male child and two xs leads to a female. 

In bees for instance this is all changed (again massively simplified) - drones are unfertilized eggs that go onto be male bees, worker bees are fertilized eggs that are not fully fertile females, and queen bees are genetically identical to workers but are reared on a different diet (royal jelly etc) that causes them to develop sexually and in other ways

[Farcanal]

Know what you're saying!

I'm well aware of the male/female genes. It's just that the embryo doesn't move to one gender or another until the actual gonad cells start to release the relevant hormones. Those cells appear about the forth week of gestation. From then on the gender is usually fixed. When the cells produce an abundance of testosterone a male child results, and of course, if they produce an abundance of aestrogen a female child is the result.

According to the info contained in the genes at conception, one set of cells will dominate over the other (but not completely stop the production of the relevant hormones by those opposing cells). This is why we all have characteristics of both genders in us.


Addendum: I am referring to humans here and that rule doesn't apply across all life but is generally so in all mammals.