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The term twin refers to two individuals who have shared the same womb, and usually, but
not necessarily, share the same birthday. Twinning normally occurs in two ways: – either the
woman releases only one ovum (egg) which divides/splits after fertilization or she produces
two separate eggs rather than the usual one. However, the type of twin that is eventually conceived
depends on what happens to the egg(s) during development. This article defines and describe the
top ten unusual and unique types of twins. Read on!
not necessarily, share the same birthday. Twinning normally occurs in two ways: – either the
woman releases only one ovum (egg) which divides/splits after fertilization or she produces
two separate eggs rather than the usual one. However, the type of twin that is eventually conceived
depends on what happens to the egg(s) during development. This article defines and describe the
top ten unusual and unique types of twins. Read on!
10. COJOINED TWINS
Conjoined twins are twins which are genetically identical. They are always of the same sex.
Besides developing from one fertilized egg, they also share same placenta and amniotic cavity.
These twins take intimacy to the extreme; sharing legs, arms, hearts, and other body organs –
even brains. Cojoined twins develop when a woman produces only one single egg which fails
to fully split after fertilization. Normally, the single embryo begins to split a few weeks
post-conception, but the separation stops it is complete.
Besides developing from one fertilized egg, they also share same placenta and amniotic cavity.
These twins take intimacy to the extreme; sharing legs, arms, hearts, and other body organs –
even brains. Cojoined twins develop when a woman produces only one single egg which fails
to fully split after fertilization. Normally, the single embryo begins to split a few weeks
post-conception, but the separation stops it is complete.
9. HALF-IDENTICAL TWINS
Half-identical or half-twins or semi-identical twins (or polar body twins) occurs when the
twins do inherit similar genes from the mother but totally different genes from the father.
They are theoretically caused when the polar body is fertilized by only one sperm at the
same time the egg is fertilized by a different sperm resulting in twins who share half their
genes in common (from the mother). But, the other half of their genes are different since
they come from two distinctively different sperm cells.
twins do inherit similar genes from the mother but totally different genes from the father.
They are theoretically caused when the polar body is fertilized by only one sperm at the
same time the egg is fertilized by a different sperm resulting in twins who share half their
genes in common (from the mother). But, the other half of their genes are different since
they come from two distinctively different sperm cells.
8. TWINS OF DIFFERENT RACE
Heteropaternal superfecundation can explain cases where dizygotic (fraternal) twins
exhibit different racial characteristics due to the different races of the parents. One
child can be white, fair-haired and light skin while the other can be black and
dark-haired. Statistics show that the chance of a mixed race couple having twins
of different colors is a million to one.
exhibit different racial characteristics due to the different races of the parents. One
child can be white, fair-haired and light skin while the other can be black and
dark-haired. Statistics show that the chance of a mixed race couple having twins
of different colors is a million to one.
7. MONOZYGOTIC TWINS
Monozygotic twins (or identical twins or enzygotic twins, or true twins, or uniovular twins)
are two offspring born of the same pregnancy, developed from one zygote
(single fertilized ovum) which later split into two equal halves during the early phase of
embryo development. This leads to the formation of two embryos each of which
develops as a separate but identical fetus. Monozygotic twins are always of same sex.
And, they have practically identical genes: possess identical blood groups, have the same
samegenetic constitution, and closely resemble each other in physical, mental and
psychological characteristics.
are two offspring born of the same pregnancy, developed from one zygote
(single fertilized ovum) which later split into two equal halves during the early phase of
embryo development. This leads to the formation of two embryos each of which
develops as a separate but identical fetus. Monozygotic twins are always of same sex.
And, they have practically identical genes: possess identical blood groups, have the same
samegenetic constitution, and closely resemble each other in physical, mental and
psychological characteristics.
6. DIZYGOTIC TWIN
The term dizygotic means “two fertilized eggs”. Dizygotic twins or fraternal twins form when two eggs are
The term dizygotic means “two fertilized eggs”. Dizygotic twins or fraternal twins form when two eggs are
fused and fertilized by two separate resulting into two separate zygotes. In most circumstances,
women only release a single egg in one ovulation cycle. However, sometimes multiple eggs may
be released in one cycle leading to dizygotic twins. They can be of the same sex or different sex.
These twins have their own separate placentas, chorions and amniotic sac.
women only release a single egg in one ovulation cycle. However, sometimes multiple eggs may
be released in one cycle leading to dizygotic twins. They can be of the same sex or different sex.
These twins have their own separate placentas, chorions and amniotic sac.
5. MIRROR IMAGE TWINS
Mirror twins originate from one fertilized egg. They basically form the same way as
monozygotic twins. The only difference is that image twins tend to develop reverse
asymmetric features i.e. when one is right handed, the other is left-handed. When they
face each other, they are the exact mirror reflection of themselves. This is something
that is normally attributed to a delayed split of the fertilized egg, often seven days after
conception. Other reverse asymmetric features include such opposite thumbs, hair
whorls that swirl in opposite directions and birthmarks on opposite sides of their body.
It is said that 25% of identical twins (monozygotic twins) tend to be mirror image twins.
monozygotic twins. The only difference is that image twins tend to develop reverse
asymmetric features i.e. when one is right handed, the other is left-handed. When they
face each other, they are the exact mirror reflection of themselves. This is something
that is normally attributed to a delayed split of the fertilized egg, often seven days after
conception. Other reverse asymmetric features include such opposite thumbs, hair
whorls that swirl in opposite directions and birthmarks on opposite sides of their body.
It is said that 25% of identical twins (monozygotic twins) tend to be mirror image twins.
4. TWINS WITH DIFFERENT BIRTHDAYS
This is a situation where the twin A is born at say, 11:56pm and the twin B is born at
12:02am the followingday. Or, it could be in different years, say twin number one is
born on 31st December and the second one is born on 1st of January the following years.
12:02am the followingday. Or, it could be in different years, say twin number one is
born on 31st December and the second one is born on 1st of January the following years.
3. PARASITIC TWINS
Parasitic twins are formed when conjoined twins develop asymmetrically/disproportionately
with the stronger baby supporting the weaker one. The name comes from the fact that the
weaker twin (parasitic twin)depends on the stronger one for survival. A parasitic twin may
consist of abnormal cell growth e.g. extra limbs. The stronger twin may also develop an
abnormal mass of cell inside its body, what is referred to as “fetus in fetu.”
with the stronger baby supporting the weaker one. The name comes from the fact that the
weaker twin (parasitic twin)depends on the stronger one for survival. A parasitic twin may
consist of abnormal cell growth e.g. extra limbs. The stronger twin may also develop an
abnormal mass of cell inside its body, what is referred to as “fetus in fetu.”
2. SUPERFETATION TWINS
The term superfetation is used where a fetus is formed when another fetus is already in
the uterus. Superfetation happens when a women ovulates more than one egg but the
eggs are released at different times, sometimes up to 24 days apart, and they are fertilized
when they are released i.e. two separate occurrence of fertilization taking place during the
same cycle. It is an unusual event among humans, but is commonly experienced among animals.
the uterus. Superfetation happens when a women ovulates more than one egg but the
eggs are released at different times, sometimes up to 24 days apart, and they are fertilized
when they are released i.e. two separate occurrence of fertilization taking place during the
same cycle. It is an unusual event among humans, but is commonly experienced among animals.
1. HETEROPATERNAL SUPERFECUNDATION TWINS:
TWINS WITH DIFFERENT FATHERS
Twins can have different fathers. One well-known case was described in 1810 in the
US. A woman had both a white and a black lover, and she became pregnant and gave
birth to twins, one white and the other black. Each twin had a different father. This is
called superfecundation. It happens when the mother ovulates more than one egg and
has more than one partner during her fertile period. One egg is fertilized with sperm from
one partner, and the other egg from sperm of the second partner. These types of twins
are always fraternal or dizygotic.
US. A woman had both a white and a black lover, and she became pregnant and gave
birth to twins, one white and the other black. Each twin had a different father. This is
called superfecundation. It happens when the mother ovulates more than one egg and
has more than one partner during her fertile period. One egg is fertilized with sperm from
one partner, and the other egg from sperm of the second partner. These types of twins
are always fraternal or dizygotic.