Question

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.

Short answer

Answer: The development of a freemartin calf might occur due to shared fetal circulation between fraternal twins, where the presence of male hormones, such as testosterone from the male calf, influence the development of the female calf. The masculinized reproductive organs in the female calf caused by the influence of these male hormones result in sterility.

Step-by-step solution

Understanding the terms

Fraternal twins refer to offspring that develop from two different eggs and can be of different sexes. Freemartin is a term used when a female calf is born as a fraternal twin with a male calf and has certain masculinized features resulting in sterility.

Discussing the placental connection

In cows, fraternal twins may share a common placenta, which results in shared fetal circulation. This means that blood and various substances carried in the blood (including hormones) can be exchanged between the two developing fetuses.

Considering the role of hormones

Hormones play a crucial role in the development of an organism, including its reproductive organs. In the case of fraternal twins sharing a placenta, both male and female hormones will be present in the shared circulation.

Predicting the effect of male hormones on the female twin

The presence of male hormones (testosterone) from the developing male calf in the shared circulation can masculinize the developing female calf, which could alter the development of her reproductive organs and cause them to become more like male organs. This could lead to the female twin being sterile as the masculinized reproductive organs are not functional for reproduction.

Conclusion

The development of a freemartin calf can be predicted as a result of shared fetal circulation between fraternal twins, where the presence of male hormones, such as testosterone, from the male calf influence the development of the female calf. The masculinized reproductive organs in the female calf, caused by the influence of male hormones, result in sterility.