Artist got it wrong, two sperm cannot fertilize one egg to produce twins, it's either two eggs are fertilized to produce fraternal twins or one egg is fertilized and the embryo splits early in development to produce identical twins.
Artist got it wrong, two sperm cannot fertilize one egg to produce twins, it's either two eggs are fertilized to produce fraternal twins or one egg is fertilized and the embryo splits early in development to produce identical twins.
Semi-identical twins, confirmed case in 2007. Both are chimeras. The exact mechanism is unknown, but the more likely case is the formation of a triploid zygote via dispermic fertilization, which then cleaves 'imperfectly' into a chimeric blastomere. If twinning occurs later this would result in chimeric twins.
Dispermic fertlization is expected to occur in 1% of cases. Most will end with an abnormal 'zygote' that cannot cleave properly and will fail to implant.
Some zygotes will survive the embyrogenesis process (usually by shedding excess chromosomes to arrive as close as possible to a diploid state) and implant. These are likely to have significant genetic abnormalities (like say, XXY sex chromosomes), and may fail to develop into a baby.
