Question

a female ovary produces one of them at a time every month this and please tell not more than one zygote can be formed at a time I were transferred yours then also find out why some twins are identical and some not

Answer 1

some ovaries are fertilised by two same kind of sperms at a time which gives identical twin ..
some ovaries are fertilised by two different types of sperms at a time which gives unidentical twins.

Answer 2

HI
HERE IS THE ANSWER

In a multiple pregnancy, there is more than one baby growing in the womb (uterus) at the same time. Being pregnant with twins is the most common example. Both mother and babies need extra monitoring during pregnancy as the risks are higher than in a singleton pregnancy.


Fraternal TwinsFraternal Twins (commonly known as "non-identical twins") usually occur when two fertilised eggs are implanted in the uterine wall at the same time that is when the mother releases two eggs and both become fertilized by two different sperms. The two eggs form two zygotes. and these twins are therefore also known as dizygotic.
Dizygotic twins. like any siblings. have a very small chance of having the exact same chromosone profile. but most likely have a number of different chromosones that distinguish them. Dizygotic twins may be a different sex or the same sex. just as with any other siblings. Like singleton siblings. they share 50% of their DNA.
Studies show that there is a genetic basis for fraternal twinning ;that is. non-identical twins do run in families. However. it is only the female that has any influence on the chances of having fraternal twins as the male cannot make her release more than one ovum. Your likelihood of having fraternal twins is dependent upon the woman carrying a fraternal twin gene and can also be affected by heredity. race. marital age and number of children previously born. Two-thirds of all twin births result in same sex fraternal twins and one-third are different sex fraternal twins. About two-thirds of all twin births are fraternal.Identical TwinsIdentical Twins occur when a single egg is fertilized by a single sperm to form one zygote (monozygotic) but the zygote then divides into two separate embryos. The biological mechanisms that prompt the single fertilized egg to split in two remain a mystery. The two embryos develop into foetuses sharing the same womb. Depending on the stage at which the zygote divides. identical twins may share the same amnion (in which case they are known as monoamniotic) or not (diamniotic). Diamniotic identical twins may share the same placenta (known as monochorionic) or not (dichorionic). All monoamniotic twins are monochorionic.The later in pregnancy that twinning occurs. the more structures will be shared. Zygotes that twin at the earliest stages will be diamniotic and dichorionic ("di-di"). Twinning between 4 to 8 days after fertilization typically results in monochorionic-diamniotic ("mono-di") twins. Twinning between 8 to 12 days after fertilization will usually result in monochorionic-monoamniotic ("mono-mono") twins. Twinning after 12 days post-fertilization will typically result in conjoined twins.   

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