How do fraternal twins differ from identical twins
Fraternal twins and identical twins are two types of twins that differ in terms of their formation and genetic makeup.
1. Formation:
- Fraternal twins: Fraternal twins are formed when two separate eggs are fertilized by two different sperm. Each twin develops its own placenta, amniotic sac, and individual genetic makeup. They can be the same or different sexes and share approximately 50% of their genes, just like regular siblings.
- Identical twins: Identical twins, also known as monozygotic twins, are formed when a single fertilized egg splits into two separate embryos during the early stages of development. They share the same placenta, amniotic sac, and genetic makeup, making them genetically identical to each other. Identical twins are always the same sex.
2. Genetic Makeup:
- Fraternal twins: Fraternal twins are no more genetically similar than any other siblings born in separate pregnancies. They can have different physical appearances, distinct individual personalities, and can even look unrelated. Fraternal twins share only half of their genetic material on average.
- Identical twins: Identical twins have identical DNA as they originated from the same fertilized egg. They typically share similar physical features, such as hair color, eye color, and facial structure. Identical twins often have strikingly similar appearances and may even have some shared mannerisms.
3. Rates of Occurrence:
- Fraternal twins: Fraternal twins are more common than identical twins. The occurrence of fraternal twins can be influenced by several factors, including maternal age, genetics, ethnicity, and fertility treatments. Fraternal twins can run in families, but it is not a direct inheritance.
- Identical twins: Identical twins are less common than fraternal twins. Their occurrence is mostly random and not influenced by any external factors. Identical twins do not run in families; rather, they occur by chance during early embryo development.
In summary, fraternal twins result from the fertilization of two separate eggs by two different sperm, while identical twins are formed when a single fertilized egg splits into two separate embryos. Fraternal twins are genetically distinct and can be different sexes, while identical twins are genetically identical and are always the same sex.