Sex chromosomes are one of the main determinants of sex in multicellular organisms, and they differ from autosomes in a number of specific characteristics that may be the cause or consequence of their unique function. Since their discovery in 1905, their special characteristics have been investigated through theoretical and statistical models. After the development of molecular research methods in biology, research was mainly targeted at defining their genes and the pathways that influence sex differentiation. Through this research it has been shown that the chromosomes of vertebrates have an extremely diverse and dynamic structure. Because of that their evolution has become a great puzzle. Of course, this put the previous theoretical considerations to the test and raised very important questions that still do not have a direct answer. As part of this work, I will try to answer the following questions: what are the basic characteristics of sex chromosomes; what paradigms have been established for their origin and do experimental evidence in vertebrates match what was previously tought; has the research of sex chromosomes of vertebrates reached its peak and what else awaits us?