2.4 Fertilization and implantation

. Fertilization and implantation Fertilization occurs when a haploid sperm fuses with a haploid ovum to form a fertilized egg or diploid zygote. XII Std Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Human Reproduction Twins are two offsprings produced in the same pregnancy. ➢  Monozygotic (Identical) twins are produced when a single fertilized egg splits into two during the first cleavage. They are of the same sex, look alike and share the same genes. ➢  Dizygotic (Fraternal) twins are produced when two separate eggs are fertilized by two separate sperms. The twins may be of the same sex or different sex and are non-identical. ➢  Siamese (United) twins are the conjoined twins who are joined during birth.