A pair of modern chickens
Scientists found that all domesticated chickens have the two alleles of TSHR. The amount of domesticated chickens containing the TSHR gene spiked during the medieval era in Europe. This occurred due to the Benedictine reform in the United Kingdom. Religious fasting for Christians was required and eating four-legged animals was prohibited. However, two-legged animals were acceptable to eat. That is how chickens became widely consumed and bred. Over time, the fatter chickens that reproduced more eggs had the TSHR gene and the traits were passed down.
Today, this genetic prevalence of the TSHR gene shows the human role in selection. Naturally, people wanted to eat the fatter chickens and the chickens who would lay eggs every day. Unbeknownst to us at the time, chickens who satisfied these "requirements" had the TSHR gene. As these chickens bred, they reproduced offspring who also had the dominant genetic traits. I think this evolution of chicken genomics is fascinating because it demonstrates how human decisions have impacted chickens today. The consumption of chicken following the Benedictine reform puts into perspective the correlation of the influence of artificial selection on modern genetics.