• Question: What decides if a baby is male or female?

    Asked by Lula Farguell to Anais, katy, Lauren, Richard, Stuart on 11 Mar 2016.
    • Photo: Lauren Laing

      Lauren Laing answered on 11 Mar 2016:

      Great question Lula! For humans sex is determined by two chromosomes, X and Y. A female is XX, and a male is XY. Because women completely lack the Y chromosome, they always contribute an X chromosome to the baby. The sex is determined by whether the sperm from the father that fertilizes the egg is carrying another X or a Y.

      As a fish biologist of course I must also tell you about fish!!!

      For some fish species, like humans, they have a chromosome which is linked to which sex they will be, if they are males of females. Other species are more flexible, for example in some species, such as salmon, goldfish and tilapia, the sex of an embryo is determined by the temperature of the water in which it is grown! For the zebrafish (one of the fish I study), we still haven’t found a definitive answer regarding how the sex of the embryo is determined! This is really interesting, because lots of people research this species, or keep them in their aquarium at home! We know a lot about their genes and how they work, but we haven’t answered this question yet!!

    • Photo: Stuart Atkinson

      Stuart Atkinson answered on 14 Mar 2016:

      Thanks Lauren. Yes’ it’s as simple as that. We have 23 sets of chromosomes and the pair responsible for gender look like an ‘X’ in women and a ‘Y’ in men.

    • Photo: Richard Friend

      Richard Friend answered on 14 Mar 2016:

      It isn’t as simple as a 50/50 chance of being born a boy or a girl in humans. They reckon that the environment that a pregnant woman is in can effect the hormones in the woman and change the probability of the the gender of her child. Slightly more males are born than females to account for a higher male infant mortality rate, which means that we end up with more females overall.

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