Differences between Fraternal Twins and Identical Twins
Contents
Fraternal twins vs. Identical twins[edit]
Twins are two offspring produced from the same pregnancy.[1] They are categorized into two main types, dizygotic (fraternal) and monozygotic (identical), based on how they form.[1][2] The primary distinction between them is genetic. Fraternal twins originate from two separate eggs fertilized by two different sperm, while identical twins develop from a single fertilized egg that splits into two.[3]
Fraternal twins, also called dizygotic twins, occur when a woman's ovaries release two eggs, and each is fertilized by a different sperm.[4][5] This results in two separate zygotes, each developing with its own placenta and amniotic sac.[5] Genetically, they are as similar as any other siblings, sharing about 50% of their DNA. Consequently, fraternal twins can be of the same or different sexes and may not look more alike than other siblings.[4]
Identical twins, or monozygotic twins, are formed when a single fertilized egg splits into two separate embryos. This division happens randomly in the early stages of development.[2] Because they originate from one zygote, identical twins are genetically nearly identical and are almost always the same sex. They share the same genes, which results in very similar physical traits, such as hair and eye color. However, environmental factors can cause minor differences in appearance.[2] While their DNA is the same, identical twins have different fingerprints.[2]
Comparison Table[edit]
| Category | Fraternal Twins | Identical Twins |
|---|---|---|
| Scientific Name | Dizygotic (two zygotes)[2] | Monozygotic (one zygote)[2] |
| Formation | Two separate eggs are fertilized by two separate sperm.[3] | A single fertilized egg splits into two embryos.[3] |
| Genetic Makeup | Share approximately 50% of their DNA, like typical siblings. | Genetically almost identical. |
| Sex | Can be the same or different sexes.[4] | Almost always the same sex. |
| Physical Appearance | Resemblance is similar to any other siblings.[4] | Very similar in appearance, with the same hair and eye color.[2] |
| Blood Type | May have different or the same blood types. | Almost always have the same blood type. |
| Heredity | The tendency for hyperovulation can be inherited. | Not considered hereditary; occurs by chance.[2] |
Zygosity Testing[edit]
At birth, it can sometimes be difficult to determine if twins are identical or fraternal based on appearance or examination of the placentas alone. The most definitive method for determining zygosity is a DNA test.[3] By comparing genetic markers, a test can confirm whether the twins' DNA profiles are identical. Knowing a twin pair's zygosity can be important for health reasons, as identical twins may be susceptible to the same genetic illnesses and are compatible for organ transplants.[3]
References[edit]
- ↑ 1.0 1.1 "wikipedia.org". Retrieved November 07, 2025.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 "twinstrust.org". Retrieved November 07, 2025.
- ↑ 3.0 3.1 3.2 3.3 3.4 "betterhealth.vic.gov.au". Retrieved November 07, 2025.
- ↑ 4.0 4.1 4.2 4.3 "raisingchildren.net.au". Retrieved November 07, 2025.
- ↑ 5.0 5.1 "parents.com". Retrieved November 07, 2025.
