Question

When does twinning occur during sexual reproduction?

Answer 1

when the sperms travel through the fallopian tube the sperms try to break the thick covering of ovum.theres a competition between the sperms to break the wall of ovum but sometimes 2 sperms at a time break the wall and entre together which results in twins!
hope it helps u and you understand it!

Answer 2

This occurs when the zygote starts to split after day 12 following fertilization and fails to separate completely. This condition occurs in about 1 in 50,000 human pregnancies.