Yes, twins can be one boy and one girl.
Twins come in two main types: identical (monozygotic) and fraternal (dizygotic). The possibility of having one boy and one girl is exclusive to fraternal twins.
Fraternal Twins and Sex
Fraternal twins result from two separate eggs being fertilized by two separate sperm. Because of this, they are no more genetically similar than any other siblings. Consequently, they can be:
- Both boys
- Both girls
- One boy and one girl
The reference states: "they can be assigned different sexes at birth and may also identify as different genders". This confirms that fraternal twins can indeed be different sexes.
Identical Twins and Sex
Identical twins develop from a single fertilized egg that splits into two. They share virtually the same DNA. Typically, identical twins are always the same sex. Although very rare, variations can occur in identical twins where differences in sex chromosomes might lead to one twin presenting with characteristics that differ from the other.
