[Biology Class Notes] on Difference Between Identical and Fraternal Twins Pdf

How are Identical and Fraternal Twins Formed?

A single pregnancy resulting in two offspring is termed as twins. Twins are of two types; when both the offspring are identical, it’s termed as monozygotic (identical), which means they are developed from a single zygote splitting to form two embryos; and when they are not identical, it’s termed as dizygotic (fraternal), which means developed from separate eggs.

In most cases, a singleton takes birth which means an offspring developed from a single egg, alone in a womb. When two biologically unrelated individuals look-alike, they are termed as doppelgangers.

Identical Twins

Identical Twins appear from the fertilisation of a single egg that splits in two. They are also known as monozygotic twins. Identical twins are always of the same sex and share each common genes. About one in three sets of twins are identical. This happens because the fertilised egg splits in two while it is still a tiny gathering of cells. The self-sustaining halves then form into two babies, with the equivalent genetic information. Twins conceived from one sperm and one egg are termed as (one-cell) identical or ‘monozygotic’ twins. The biological mechanisms that indicate the single fertilised egg to split in two remain a mystery. About one-quarter of identical twins are mirror images of one another, which suggests that the right side of one child resembles the left side of their twin. 

Fraternal Twins

Fraternal twins emerge from the fertilisation of two separate eggs during the same pregnancy. Fraternal twins have single DNA and can change. Fraternal twins are basically two completely individual siblings with no distinct physiological similarity, however, due to their varied developmental rates they pose challenges for health care providers. Fraternal twins are also known as dizygotic twins, indicating two fertilised eggs. They’re the outcome of the mother releasing two eggs at the same time with each egg being fertilised by a different sperm.

As they come from different sperm and eggs, they only bestow about 50 per cent of their chromosomes similar to other siblings. This implies they can be identical or different sexes and aren’t indistinguishable.

Fraternal Twins or Identical Twins

Similar sex twins with separate placentas can be identical or fraternal. It is essential to know whether your twins are identical and fraternal for health reasons. To discover whether twins are identical or fraternal, one can ask for a genetic test after the babies are born. This test is known as the zygosity test. This test doesn’t hurt and includes sample collection of cheek cells of babies by coating the inside cheeks with a soft applicator. 

Identical twins are more likely to get the same illness, unlike fraternal twins. If one of a pair of identical twins is diagnosed with a health condition, the other twin should be monitored often for early symptoms.

Some of the reasons why twins and parents of twins require to recognise whether they’re identical or fraternal includes:

• possibility of having more twins in future pregnancies 

• Being sure that they have accurate knowledge about their genetic make-up

• Being able to explain their family, friends and others

• Being involved in twin research

Some identical twins are also identified as mirror twins. For example, they are handed oppositely, their hair parts on opposite sides or they have birthmarks on opposite sides of their body. There are also instances of mirrored internal organs among identical twins.

Let us glance at the difference between identical twins and fraternal twins presented in a tabular column below.

Difference Between Identical Twins and Fraternal Twins