Extremely Rare Semi-Identical Twins In Australia
Semi-identical twins are extremely rare, with only one other case documented before.
Transcript
00:00 Not all twins are fraternal or identical.
00:02 In Australia, semi-identical twins were born.
00:05 What does that mean?
00:06 [music]
00:10 So normally, a developing embryo will get one set of chromosomes from the mom's egg
00:15 and the other set of chromosomes from the father's sperm.
00:17 In fraternal twins, two separate sperm cells fertilize two separate eggs
00:21 and those develop into the twins.
00:22 So the babies share about 50% of their mom's genes and 50% of their dad's genes.
00:28 In identical twins, a single sperm fertilizes a single egg,
00:32 which means that that fertilized egg then divides into the two twins
00:35 and they end up sharing 100% of both their mom's and their dad's genes.
00:39 So in semi-identical twins, something different happens.
00:42 Two separate sperm fertilize the same egg.
00:45 So then these babies share 100% of their mom's DNA,
00:49 but they only share a proportion of their dad's, in this case 78%.
00:53 This is extremely rare.
00:54 This has only been documented once before in twins that were born in the U.S.
00:59 The twins are now four and a half years old,
01:01 and though there were a few complications after they were born,
01:03 they're now developing normally.
01:05 They are a boy and a girl, which actually doesn't happen in identical twins.
01:08 In identical twins, since they share 100% of their genes,
01:11 it's either a girl and a girl or a boy and a boy.
01:13 However, semi-identical twins are so rare that researchers don't think routine testing is warranted.
01:18 [MUSIC]