Twin

Twin

A twin is one of two offspring produced in the same pregnancy. Twins can be either monozygotic (identical), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic (fraternal), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.

Types of twins

Twins can be classified into two main types: monozygotic and dizygotic.

Monozygotic

Monozygotic twins, also known as identical twins, occur when a single egg is fertilized to form one zygote which then divides into two separate embryos. Monozygotic twins share the same genetic material, are always the same sex, and look very similar.

Dizygotic

Dizygotic twins, also known as fraternal twins, occur when two separate eggs are fertilized by two separate sperm. Dizygotic twins share about 50% of their genetic material, can be the same sex or different sexes, and generally look no more similar than siblings.

Twin studies

Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in content fields, from biology to psychology.

See also

• Multiple birth
• Twin study
• Vanishing twin
• Conjoined twins

References

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