FertiScramble: Fertilisation Race

Based on a classic ZX Spectrum cave-flying game, itself a clone of Konami’s 1981 arcade game Scramble.

The science

You guide a sperm cell (spermatozoon) through five zones of the female reproductive tract, each opening with a short fact about what happens there:

• Vagina: acidic, which many sperm cells don’t survive.
• Cervix: cervical mucus filters out sperm cells that swim poorly or have an abnormal shape.
• Uterus: leukocytes, mostly neutrophils, engulf many sperm cells.
• Fallopian tube: only a few thousand sperm cells get this far, and they complete capacitation, their final maturation.
• Ampulla: the widest part of the tube, where fertilisation usually happens.

On the way, plasma cells in the mucosa release antibodies against sperm, and your energy comes from fructose, the sugar in seminal plasma that sperm cells use as fuel.

At the egg comes the acrosome reaction. The acrosome, a cap on the front of the sperm head, releases enzymes: hyaluronidase disperses the corona radiata (the layer of follicle cells around the egg), and acrosin digests a path through the zona pellucida, the glycoprotein coat of the oocyte. Then the membranes of the sperm cell and the oocyte fuse, and the result is a zygote, the first cell of a new embryo.

In the cervix and the Fallopian tube you may find a sperm reservoir: in life, sperm cells are stored in the folds of the cervix and in the tube, and released in waves over hours to days, which gives you an extra life.

Where the game cuts corners

• Sperm cells don’t fire their enzymes like shots. The acrosome reaction happens once, when the sperm cell meets the egg’s coat, and releases the enzymes in one go.
• Sperm cells don’t make the journey only by swimming: muscle contractions of the uterus and the Fallopian tube help to carry them, and the egg moves too.
• And no sperm cell gets three lives, or five: in life, each has a single try.