Heterozygotenüberlegenheit

Heterozygotenüberlegenheit, also known as heterozygote advantage, is a phenomenon in genetics where individuals who are heterozygous for a particular gene have a higher fitness than individuals who are homozygous for the same gene. Fitness, in an evolutionary context, refers to an organism's ability to survive and reproduce. This means that heterozygous individuals are more likely to pass on their genes to the next generation.

This type of advantage can arise for several reasons. One common mechanism is that the heterozygote state confers resistance to certain diseases. A classic example is sickle cell anemia. Individuals homozygous for the sickle cell allele (HbS/HbS) suffer from severe anemia and often die before reproducing. Individuals homozygous for the normal allele (HbA/HbA) are susceptible to malaria. However, individuals heterozygous for both alleles (HbA/HbS) have a degree of protection against malaria and do not suffer from severe sickle cell anemia. This makes them fitter in regions where malaria is prevalent.

Another reason for heterozygote advantage is that the heterozygote may have a broader range of adaptability to different environmental conditions. For instance, a plant that is heterozygous for genes controlling flowering time might be able to flower and reproduce successfully in a wider range of temperatures or rainfall patterns than a homozygous plant. This increased adaptability can be a significant advantage in a fluctuating environment.

The concept of heterozygote advantage is important in understanding the maintenance of genetic diversity within populations. It explains why certain alleles, even those that might appear detrimental in their homozygous state, can persist at relatively high frequencies. This genetic variation is crucial for the long-term survival and evolution of species.