Feb A set of twins born in Queensland are more than just adorable. The brother and sister were born in , but it took medical experts that long to figure out just exactly what happened to make their lives possible. They are only the second pair of semi-identical twins ever identified. In the case of identical twins, one sperm fertilises an egg, which later splits into two embryos.
How sperm succeed: widespread selfish genes
Doctors confirm new type of twin born from one egg and two sperm | Reuters
There are many different kinds of twins, including fraternal twins two eggs and two sperm , identical twins one egg and one sperm , mirror image identical twins separation on day 5 of development , identical twins with two placentas, one placenta and two sacs, one placenta and one sac, and finally conjoined identical twins separation after day 10 with the fetuses attached , always with one placenta and one sac. Uterus, fallopian tube and ovary. Shows steps of ovulation, fertilization and early development. Most twinning occurs between first 30 hours and days. A: divides at two cell stage most identical.
'Semi-identical' twins discovered
Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, and supporting structures. Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2. If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA.
CNN You've probably heard of identical and fraternal twins, but a report published Thursday says there's a third kind -- sesquizygous twins or "semi-identical. Identical -- or monozygotic -- twins pop up from a single fertilized egg that eventually splits in two and forms two identical boys or two girls. Fraternal -- or dizygotic -- twins form from two eggs that have been fertilized by two of the father's sperm, producing two genetically unique siblings. But "semi-identical" twins are so rare, experts say they have only identified two cases -- ever.