The story

The Beckhams announced last week that they are expecting their fourth child and after three boys they may well be hoping for a girl this time.  But, in an interview in Vogue which took place before the announcement, Victoria has said that this looks highly unlikely.

But does it?

Well, looking purely at the fact that 50% of sperm carry an X chromosome and 50% carry a Y chromosome then she has just as much chance of conceiving a girl this time round then she did in her previous pregnancies – 50:50.

However, some interesting research published over 10 years ago by Dr Valerie Grant, a reproductive scientist at the University of Auckland, presented a theory that dominant women have high levels of testosterone  and are much more likely to give birth to boys.  The reason is, she hypothesises, is that this type of woman is much more suited to raising boys as her extra boost of this hormone makes her more assertive.  Women who only have girls have lower levels of testosterone which make them nurturing, empathic and tolerant and supposedly therefore better at bringing up girls.

She gathered scientific evidence for her theory in 2008 by collecting data using cows.  She found that high levels of testosterone in the follicles will reliably produce a male embryo because the egg produced will be adapted to receive a Y chromosome.  Therefore, the woman has already decided the sex of her baby before fertilisation occurs.

So the answer to the Beckhams having a girl?  Posh needs to be less confident, assertive and influential.  Not something I see happening anytime soon…

Teaching idea/resource

I thought that this story would make a nice spin on teaching about sex chromosomes and how sex is determined to a KS4 class.

The Beckham’s baby PowerPoint I produced takes students through what we mean by sex chromosomes, what happens to chromosomes during fertilisation and sex cell production and finishes with a Punnett square that students can use to tell the Beckhams what the probability of their baby being a girl is.

You may wish to discuss the research that I outlined above with higher ability students.  They may be interested to hear that even though you have a 50:50 chance of having a boy or a girl, the population of the Earth is never 50% men and 50% women and that this ratio is prone to fluctuations.  During both World Wars, for example, there was an increase in the number of male births.  Can they explain why using the theory presented by Dr Grant?

Weblinks:

‘Women with high testosterone may be more likely to have sons’ article from The Times

This video highlights the possibility that the Beckhams have used IVF and chosen the sex of the implanted embryo in order to make sure they have a girl.

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