When cows have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinized reproductive organs. This calf is referred to as a freemartin. In cows, twins may share a common placenta and thus fetal circulation. Predict why a freemartin develops.

Key Concepts

Freemartinism

Freemartinism is a condition observed in female calves born as twins with a male calf. The female twin, known as a freemartin, often develops masculinized traits due to the influence of male hormones from the male twin's blood supply. This occurs because the twins share a common placenta, allowing for the exchange of blood and hormones during gestation.

Sexual Differentiation

Sexual differentiation is the process by which the reproductive system and secondary sexual characteristics develop in an organism. In mammals, this process is influenced by genetic and hormonal factors, particularly the presence of the Y chromosome and testosterone. In the case of freemartins, the exposure to male hormones during critical periods of development leads to the masculinization of the female reproductive system.

Placental Sharing

Placental sharing occurs when twins share a single placenta during gestation, which can lead to the exchange of blood and hormones between the fetuses. This phenomenon is significant in the development of freemartins, as the female twin is exposed to male hormones from the male twin, affecting her sexual development and resulting in sterility and masculinized reproductive organs.