A 28-year-old woman gave birth to twins in 2014. Her set of twins shared a placenta,...

A 28-year-old woman gave birth to twins in 2014. Her set of twins shared a placenta, appearing to be identical twins.

But the 14-week ultrasound showed they were different genders -- making it impossible for them to be monozygotic twins.

These twins were formed when a single egg was fertilized by two sperm.

1. How many types of twins do exist?

2. What are "semi-identical" twins, and why are they so rare?

3. If this happen, do these embryos have fair chances of survival?

4. Which percentage of their genetic DNA do they share?

Solutions

Expert Solution

Ans.1) twins are mainly of 2 types-

1. Monozygotic twins- Here, a single zygote (formed by fusion of one sperm and one egg) splits after fertilization giving rise to 2 embryo. Such twins will be identical, will have same gender and will also be genetically identical .

2. Dizygotic twins- Here 2 zygote are formed by fertilization of 2 separate eggs by 2 different sperm. Such twins will not be identical, and their gender may be same or different and genetically also they will not be identical.

A new category of twins was recently identified-

3.Sesquizygotic twins- such twins are formed when single egg is fertilized by two different sperms.

Ans.2)Semi- identical twins are formed when single egg is fertilized by two sperms. Such twins can blhave same or different gender but are no more alike.

Semi-identical twins are rare because here after fusion 3 set of chromosomes are there in zygote which are generally incompatible.

Ans 3) if by somehow, semi-identical embryo formed, they have rare chance of survival. Because these embryos will have 100% maternal DNA but they will share a proportion of DNA from paternal side. Some cells will have chromosomes from sperm 1 or some from sperm 2. So some cell may have extra copy of same chromosomes or some lack particular chromosome. So some disorder may occur and hence there survival will not be easy.

Till now only two cases of semi-identical twins have been identified.

Ans.4) According to researchers, semi-identical twins generally share 50% genetic DNA. This may range from 50 to 100%

gladiator answered 1 year ago

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