If resistance to pathogens is genetically based, loss of alleles that confer res

Question

If resistance to pathogens is genetically based, loss of alleles that confer resistance would be detrimental to a population. An example of such resistance genes may include genes in the major histocompatibility complex (MHC) that affect control of immune response. Consider the following decisions a conservation biologist must make: Each of the three populations of salmon (each regarded as an evolutionary significant units (ESU)) is locally adapted to its natal stream. However, it has been shown that individuals that are heterozygous and outbred between ESU's are more resistant to pathogens. Outline a scenario in which maximum local adaptation could be maintained while also maintaining heterozygosity at MHC alleles. Is such a scenario possible? Explain your scenario/decision in terms of the genetic drawbacks/benefits to the populations.

Explanation / Answer

If the resistance gene in MHC, come from parents,and offspring of parents also show resistance to pathogen. And loss(delete) of resistance gene MHC alleles confirmed that resistance gene would dangerous to population.

MHC (major histocompatibility complex) genes which code for the cell-surface-protein, and they play role in adaptive immune system (like T-cell/B-cell). If the MHC gene resistance to pathogen than, pathogen will survival and reproduction to increase number of pathogen in host. That leads to kill host(salmon).

According to question- each of three population of salmon (each regard as a ESU) is locally adapted to it’s natal stream(back birthplace for reproduce), it’s show that individuals that are heterozygous (Aa) and outbred (not closely related) between EUS’s are more resistance to pathogens. Because all the individual in gene pool have resistance alleles on MHC. So when closely related (ESU’s) heterozygous salmon breed in natal stream, so there is strong possibility to have resistance gene in new population. And it’s a drawback to new population because the immune system is weak in salmons, and cell mediated immunity(adaptive immune response not played any role in salmon) so the pathogen will survive in salmons and reproduce in salmon, and due to pathogenicity of pathogen, eventually kill the salmon, because of resistance MHC gene in local natal stream salmon population (gene pool), so it would dangerous to population.

It is not possible to survive all population in locally adapted to natal stream, because if the individual reproduce or outbreed within the gene pool, than there is maximum chance to pass MHC resistance gene to next generation,

if the male heterozygous (Aa) and female(Bb) cross than the offspring AB, Ab, aB, ab, means only one will have normal gene for MHC, other 3 offspring will show resistance to pathogen. And this continuous for next generation than the homozygosity of resistance gene increase and herozygosity of normal gene decrease over a generation.

So it’s a mojar drawback because in gene pool resistance gene frequency increasing and normal dominant gene frequency decrease, so pathogenicity of pathogen more dominant in population and resistance would dangerous to population.

In one point of view, it’s benefited, because breeding in same gene pool and outbred, and mating between related heterozygous, they all pass all strong natural selected gene to next generation to quick adaptation to local environment (natal stream), so that they can adapt easily and reproduce to maintained gene pool.

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