Hair loss in men is a polygenic trait, meaning it is determined by multiple genes, not just one. However, a specific gene plays a key role in this process, and its inheritance follows rules that can be misleading.

How it works: the main gene and its characteristics

The main gene responsible for androgenetic alopecia is called the androgen receptor gene. It is located on the X chromosome. Since men receive the X chromosome from their mother and the Y chromosome from their father, this specific gene is always passed down through the maternal line.

Important: this gene is itself autosomal dominant, but with a very important qualification — its expression is strongly dependent on the level of male sex hormones. That is why it causes baldness in men, but not in women.

Is it dominant or recessive?

From a scientific point of view, in the classical Mendelian understanding, the allele of the gene predisposing to baldness is considered dominant. This means that for the trait to manifest, only one copy of this gene is needed.

• If a man has this gene on the X chromosome, it will manifest. There is no second copy on the Y chromosome to suppress it.
• A woman with two X chromosomes can be a carrier of the gene but not express it if the other X chromosome has a \"normal\" variant of the gene. This makes the gene recessive to the female sex.

Thus, this gene behaves as dominant in men and as recessive in women.

The Role of Other Genes

Although the androgen receptor gene is the main \"culprit,\" it is not the only one. Studies show that more than two hundred and fifty different genetic loci are involved in the development of baldness. Some of them are not located on sex chromosomes, but on autosomes, and can be passed from father to son, affecting the age of onset of baldness and its speed.

Conclusion

Baldness in men is a complex trait that cannot be described simply as \"dominant\" or \"recessive\". The key gene located on the X chromosome is dominant in men but recessive in women. However, the final phenotype depends on the interaction of multiple genes received from both parents, as well as on the level of hormones and other factors. Therefore, even if your grandfather on the maternal side was bald, it does not guarantee that you will definitely go completely bald, especially if there are genes in your genome that \"mitigate\" this trait.

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