Why are identical twins always the same gender?

1 Answer
mason m
Dec 18, 2015

Identical twins are monozygotic, meaning that a singular egg was fertilized, creating one zygote, which then divided into two separate embryos.

The splitting of the zygote leaves two halves of the zygote, each with the exact same genetic material.

Since gender is determined by the sex chromosomes (genetic material), and each new zygote contains identical genetic material, the same chromosomes will program the same sex in each twin.

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