Are the twins boys or girls?

Identical twins, that is, monozygotic twins, are fertilized eggs produced by combining a sperm with an egg. This fertilized egg splits into two embryos. Because they come from the same fertilized egg and receive the same chromosome and genetic material, they are of the same sex. They are just like the same mold, and sometimes even their parents are difficult to distinguish.

Homozygote is because "a fertilized egg splits into two embryos in the early stage of development" to form twins, while heterozygote is because "the mother's ovary expels two eggs at the same time and fertilizes them separately to form embryos." Identical twins are related to family inheritance (especially maternal inheritance), race (more blacks), older mothers and more births, while fraternal twins have nothing to do with the above factors, which is purely accidental. In the medical field, ovulation induction agents are often used in the treatment of infertility, so more than two eggs are often discharged, so we often hear about twins and triplets. [ 1]

twins

After fertilization, the fertilized egg splits into two identical fertilized eggs and then develops into two individuals. They are called identical twins because they come from the same fertilized egg. This similarity is not only similar in appearance, but also consistent in blood type, intelligence, and even some physiological characteristics, and susceptibility to diseases. Conjoined twins, which we often talk about, is actually such an identical twin, just because the fertilized egg is not completely divided, so some parts are connected. Because of this, most identical twins are of the same sex, and it is unlikely that one is a boy and the other is a girl. There is also a phenomenon that one of the two XYS falls off when it is separated, forming XY and XX, that is, a man and a woman. )

Fraternal twins

Fraternal twins: Women ovulate 1 time a month, and sometimes for some reason, two eggs are released and fertilized at the same time, resulting in two different fertilized eggs. These two fertilized eggs each have a set of placenta, which are unrelated to each other and are called fraternal twins. Born like ordinary brothers and sisters in appearance. Twins are mostly fraternal twins and are unlikely to be identical twins.

Half identical twins, half fraternal twins

After extensive genetic testing and investigation of a large number of twins, American scientists discovered around 2007 that there is a kind of "semi-identical twins and semi-fraternal twins" besides the original identical twins and fraternal twins. This achievement was first published in the British magazine Human Genetics, and then reprinted by the website of Nature magazine.

Fraternal twins are the most common type of twins. This kind of twins is two sperm and two egg cells meet in the fallopian tube, fertilized separately, and give birth to embryos separately. Such twins look like ordinary brothers and sisters.

X identical twins are eggs in which a sperm enters the mother's body, but in the early growth process, the fertilized egg splits into two embryos, so their genes are the same, and the twins after birth look almost identical.

The newly discovered new twin is that two sperm fertilize the same egg cell. Vivienne Sutter, a doctor at a medical center in Phoenix, USA, said that it may be that one egg started to divide, but did not separate, and then two divided eggs combined with one sperm. Then, before the egg is completely split in two, the genes begin to mix. Although two sperm combined with an egg are more likely to form a triploid fetus, rather than a diploid fetus. But in this case, the zygote divides into two cells, and each zygote has a different set of chromosomes. As a result, both children have the same genes from their mothers, but the genes from their fathers are different.

Family inheritance of twin pregnancy

Twin pregnancy has a family genetic tendency, which is maternal inheritance. Studies have shown that if a pregnant woman is one of twins, the probability of her giving birth to twins is1/58; If a pregnant woman's father or mother is twins, her chances of having twins are also high. Another study reported that 4% of mothers who gave birth to twins were twins, while only 1.7% of fathers who gave birth to twins were twins.

At the beginning of pregnancy, it is easy to find twins by ultrasound. The discomfort and reaction of twins during pregnancy are often more obvious than that of singletons.

authenticate

How to distinguish identical twins from fraternal twins?

There are many identification methods.

First of all, if the twins are of different sexes, they must be fraternal twins (except for a pair of semi-identical twins born in 200/kloc-0, one of whom is male and the other is hermaphrodite). If the gender is the same, further differentiation is needed. At birth, the doctor may tell you whether the two children are one placenta or two placentas. One placenta represents identical twins and two placentas represent fraternal twins. But this concept is wrong. Although the condition of placenta and fetal membrane has a certain relationship with the nature of twins' eggs, it is not absolute and cannot be judged by this alone.

Most people judge a book by its cover. Some twins are carved from the same mold. Most of them are identical twins, and those who don't look alike are fraternal twins. This method does have a certain scientific basis, and we call it similarity method. But appearance alone is far from enough, and it must also include some other characteristics, such as dermatoglyphics, hair color, hair shape and density, color and structure of iris of eyes, front and back hairlines, earwax, auricle, nose shape, face shape, lip shape, eyelids, dentition, middle finger hair, skin color and structure, freckles, taste ability of phenylthiourea (PTC) and so on. It seems that this method is also more troublesome.

Similarity method can also be achieved by blood group identification. Generally, several blood types should be determined jointly, such as ABO, P, MN, S, Rh, etc. The more blood types are determined, the higher the accuracy. If one or more blood types are different, they are fraternal twins. If they are all the same, they can be said to be identical twins at a certain probability level.

Another more reliable method is to identify DNA. Its working principle is similar to paternity test. Generally, nine gene loci are determined at the same time, and the reliability of identification results can reach over 99%. Twins only need to provide a little blood to complete the identification. This kind of work can be done in the forensic center.