The temperature! If it is between 31.7degrees C (89 degrees F) and 33.5 degrees C (94 degrees F) it will be a male, but if the temperature is outside that narrow 2.8 degrees than it will be a female.
The father determines the sex of the child. Whether the child is male or female depends on the combination of chromosomes in the sperm that fertilizes the egg. A man has both 'X' & 'Y'...
Genetically speaking, the gender of a baby is determined by the presence of the 'Y' chromosome (or the absence of it). If a Punnett square were to be drawn and a mono-hybrid cross carried out, you...