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Title: How twins are formed
Description: You will get all you need about how twins are formed and the types of twins
Description: You will get all you need about how twins are formed and the types of twins
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Twins are two offspring produced by the same
pregnancy
...
In fraternal twins, each
twin is fertilized by its own sperm cell
...
Statistics
The human twin birth rate in the United States rose
76% from 1980 through 2009, from 18
...
3
per 1,000 births
...
In Central Africa there are 18–30 twin sets (or 36–
60 twins) per 1,000 live births
...
North America and Europe have
intermediate rates of 9 to 16 twin sets per 1,000
live births
...
Women who have a family history of fraternal twins
have a higher chance of producing fraternal twins
themselves, as there is a genetically linked
tendency to hyper- ovulate
...
[12] Other factors
that increase the odds of having fraternal tw
maternal age, fertility drugs and other
fertility treatments, nutrition, and prior births
...
There are five common variations of
twinning, and one rare variation
...
Female–female dizygotic twins (sometimes
called "sororal twins")
...
The other two variations are monozygotic
("identical") twins:
Female–female monozygotic twins
...
Among non-twin births, male singletons are slightly
(about five percent) more common than female
singletons
...
For example, the sex ratio of birth in the
US is 1
...
07
males/female in ,However, males are also
more susceptible than females to die in utero, and
since the death rate in utero is higher for twins, it
leads to female twins being more common than
male twins
...
When two eggs are independently fertilized by
two different sperm cells, fraternal twins result
...
Fraternal twins are,
essentially, two ordinary siblings who happen to be
born at the same time, since they arise from two
separate eggs fertilized by two separate sperm, just
like ordinary siblings
...
Even if they happen to have
the same chromosome profile, they will always have
different genetic material on each chromosome, due
to chromosomal crossover during meiosis
...
However, dizygotic twins may also look very
different from each other
...
However, it is only the mother
who has any effect on the chances of having such
twins; there is no known mechanism for a father to
cause the release of more than one ovum
...
Dizygotic twins are also more common for older
mothers, with twinning rates doubling in mothers
over the age of 35
...
Monozygotic (identical) twins
Comparison of zygote development in monozygotic
and dizygotic twins
...
In 18–
30% of monozygotic twins each fetus has a
separate placenta and a separate amniotic sac
...
Fraternal
twins each have their own placenta and own
amniotic sac
...
Mechanism
Regarding spontaneous or natural monozygotic
twinning, a recent theory proposes that
monozygotic twins are formed after a blastocyst
essentially collapses, splitting the progenitor cells
(those that contain the body's fundamental genetic
material) in half, leaving the same genetic material
divided in two on opposite sides of the embryo
...
[19]
Spontaneous division of the zygote into two
embryos is not considered to be a hereditary trait,
but rather a spontaneous and random event
...
It can be used as an expansion
of in vitro fertilization (IVF) to increase the number
of available embryos for embryo transfer
...
This is in
marked contrast to dizygotic twinning, which
ranges from about six per thousand births in
Japan (almost similar to the rate of identical twins,
which is around 4–5) to 15 and more per
thousand in some parts of India and up to over
20 in some Central African countries
...
IVF techniques are more likely to create dizygotic
twins
...
Genetic and epigenetic similarity
Monozygotic twins are genetically nearly identical
and they are always the same sex unless there has
been a mutation during development
...
Identical
twins do not have the same fingerprints, due to the
fact that even in a small space inside the womb,
people have contact with different parts of this
environment, which gives small variations in the
same digital, making them unique
...
Normally
due to an environmental factor or the deactivation
of different X chromosomes in female monozygotic
twins, and in some extremely rare cases, due to
aneuploidy , twins may express different sexual
phenotypes , normally from an XXY Klinefelter
syndrome zygote splitting unevenly
...
The
DNA in white blood cells of 66 pairs of monozygotic
twins was analyzed for 506,786 single nucleotide
polymorphisms known to occur in human
populations
...
2 x 107 nucleotides, which
would imply hundreds of differences across the
entire genome
...
If they occur early in fetal
development, they will be present in a very large
proportion of body cells
...
Epigenetics refers to the level of activity of any
particular gene
...
This epigenetic modification
is triggered by environmental events
...
A study of 80 pairs of monozygotic twins
ranging in age from three to 74 showed that the
youngest twins have relatively few epigenetic
differences
...
Fifty-year-old twins had over
three times the epigenetic difference of three-yearold twins
...
However, certain characteristics become more alike
as twins age, such as IQ and personality
Title: How twins are formed
Description: You will get all you need about how twins are formed and the types of twins
Description: You will get all you need about how twins are formed and the types of twins