Question

Pls describe this in simpler terms

Pathogen-driven balancing selection is thought to maintain polymorphism in major histocompatibility (MH) genes. However, there have been few empirical demonstrations of selection acting on MH loci in natural populations. To determine whether natural selection on MH genes has fitness consequences for wild Atlantic salmon in natural conditions, we compared observed genotype frequencies of Atlantic salmon (Salmo salar) surviving in a river six months after their introduction as eggs with frequencies expected from parental crosses. We found significant differences between expected and observed genotype frequencies at the MH class II alpha locus, but not at an MH class I-linked microsatellite or at seven non-MH-linked microsatellite loci. We, therefore, conclude that selection at the MH class II alpha locus was a result of disease-mediated natural selection, rather than any demographic event.

Answer 1

Demographic event: An event contributes a kind of impact on an existing statistical unit.

The experiment was performed to analyze impact of demographic event and changes by selection on MH (major histocompatibility ) genes.

MH genes obtain changes at genetic level by exposure of pathogens. Only few of the experimental data are present to give idea about this point that selection works on MH loci gene in natural population.

When we do a cross between to parents we observe a particular frequency of each genotype. Here researcher transferred expected genotype frequency containing eggs to the river, which have preexisting observed genotype frequencies containing Atlantic salmon (Salmo salar) and observation was taken after 6 months to determine the condition that does natural selection on MH genes has any role in fitness consequences for wild Atlantic salmon in natural conditions. The differences was detected between expected and observed genotype frequencies at the MH class II alpha locus. here is no differences observed in MH class I-linked microsatellite or at seven non-MH-linked microsatellite loci.

Conclusion : Pathogen affected natural selection onj MH class II locus are main factor for changes

Overall: we mixed two different frequency ( observed and expected) containing eggs of Atlantic salmon and observed the changes generated in the MHC locus and concluded the responsible factor for it. We determined on which locus the changes was appeared due to natural selection after exposure of pathogens.

Thanks.