Choosing a mate involves many brain processes, with attraction geared towards producing viable offspring with a strong immune system. Histocompatibility measures the similarity of immune system genes between individuals, with MHC genes forming a group of genes concentrated on one area of a chromosome. Females use their sense of smell to find mates with different MHCs, but medical technology can interfere with this. Having several MHC genes puts a competitor at an advantage in mate selection. High histocompatibility is vital in avoiding organ rejection after transplants.
The factors that go into choosing a mate are often a mystery, even to the one making the choices. Many underlying processes in the brain combine to create a feeling of attraction. Most of them are geared towards producing viable offspring with the best chance of survival. An important factor in survival is a strong immune system, which results from dissimilar immune systems in the parents combining to create a more comprehensive defense system. Histocompatibility is the measure of how similar the genes that govern the immune system are between individuals.
Histocompatibility-relevant genes are those that recognize foreign agents invading the body and mount an immune response to fight them. These genes form a haplotype, or group of genes concentrated on one area of a chromosome, called a major histocompatibility complex or MHC. Sometimes MHC genes recombine, but generally the haplotype is passed on intact from parent to offspring. In humans, MHC is also called human leukocyte antigens or HLA.
MHC genes are codominant, so offspring express all the genes they inherit from both sides. This means that if the parents have different MHC genes, the offspring will be able to recognize the set of all foreign materials that the mother and father could recognize. To ensure that offspring have the best possible defense against disease, a prospective parent should seek out a mate with a different MHC.
The task of mate selection based on MHC genetic makeup falls to females, who are generally more discriminating in mate selection. They use their sense of smell to find mates that have different MHCs. Studies have found that women find the smell of T-shirts belonging to men with MHC other than their own more attractive. This selection method is subconscious; Sometimes women miss a smell but still feel attraction after smelling a shirt.
Medical technology sometimes interferes with these perceptions. For example, women who take birth control pills change their hormone levels. Their bodies are hormonally pregnant and in this state the impulse to select mates is dampened. The sense of smell that helped them find genetically suitable mates no longer works.
In mate selection, having several MHC genes puts a competitor at an advantage. A high degree of histocompatibility, or similar MHC genes, is vital in other situations. For example, high histocompatibility between donors and hosts is key to avoiding organ rejection after transplants.
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