"Girls' sperm" refers to sperm carrying the X chromosome, which determines female offspring. X-chromosome sperm are generally slower than sperm carrying the Y chromosome (which determines male offspring).
Why X-Chromosome Sperm are Slower
The key difference lies in size. X-chromosome sperm are slightly larger than Y-chromosome sperm. This difference in size affects their motility:
- Size and Speed: The larger size of X-chromosome sperm makes them slightly heavier and thus, slower swimmers.
- Shettles Method: This difference is the basis for the Shettles method, which suggests timing intercourse to favor conception of a particular sex. This method suggests that because X-chromosome sperm are slower but live longer, having intercourse a few days before ovulation may increase the chances of conceiving a girl.
Summary
In short, X-chromosome sperm, associated with female offspring ("girls' sperm"), are considered to be slower than Y-chromosome sperm, associated with male offspring. This difference is attributed to their slightly larger size.
