Non-Identical Twins: NCERT Solutions- Human Reproduction

Non-identical twins, also known as fraternal twins, are twins that result from the fertilization of two separate eggs by two separate sperm. They are not genetically identical and can be of the same or opposite sex. The occurrence of non-identical twins is more common than identical twins and is influenced by various factors including age, race, and family history.

Factors influencing the occurrence of non-identical twins

1. Age: Women who are over the age of 35 are more likely to have non-identical twins as they tend to release more than one egg during ovulation.

2. Family history: Non-identical twins are more likely to occur in families with a history of multiple births.

3. Fertility treatments: The use of fertility treatments such as in vitro fertilization (IVF) can increase the chances of having non-identical twins.

4. Race: Non-identical twins are more common in African and African-American populations.

Development of non-identical twins

Non-identical twins develop from two separate fertilized eggs, each of which grows into a separate embryo. Each embryo has its own amniotic sac and placenta, which means that they do not share the same blood supply. This also means that non-identical twins can have different genetic and physical characteristics.

Unlike identical twins, non-identical twins do not share the same genetic material and can be of different sexes. In some cases, non-identical twins may look very similar, but this is not always the case.

Conclusion

In conclusion, non-identical twins result from the fertilization of two separate eggs by two separate sperm. They are influenced by various factors including age, family history, fertility treatments, and race. Unlike identical twins, non-identical twins do not share the same genetic material and can be of different sexes.

Non identical twins is called the dizygotic twins (fraternal twins) are produced from the independent release of two secondary oocytes and is subsequent fertilization.
They are the same age and in the uterus at the same time but genetically they are as dissimilar as and other siblings.
It may or may not be the same sex.