Question: what is the percentage of having a baby a boy or girl ? is it possible to have a girl and boy twin ?

Vicky Forster answered on 22 Nov 2013:

Hello again popps!

Good question – it is almost exactly a 50/50 chance of having a boy or a girl I believe. It is the sperm from the man which control gender, and they are just as likely to carry an X or a Y chromosome. This then combines with an X from the woman in the egg gamete(women have only X chromosomes) and if the fertilised egg is XX, it is female, and if XY, male. It is possible to have a girl and boy twin, but not-identical twins. In identical twins – they share the same genetic information, including the same XX or XY sex chromosomes. However it is entirely possible to have non-identical twins which are girl and boy. This is where more than one egg gets fertilised by different sperm. The sperm have a 50/50 chance of carrying an X or a Y chromosome – so there is an equal chance of non-identical twins being girl-boy, boy-boy or girl-girl. This is as far as I know anyway, it is possible there are some more complicated reasons that might make it more likely for some people to have boys, girls, identical or non-identical twins – but I’m not aware of them.

Good question, I hope my answer helps!