Which statement best describes a keystone species
a) it has little genetic variation
b) it has an extremely high population
c) it remains unaffected by all environmental changes
d) it has a strong influence on the ecosystem
e) it's the first species to populate a new ecosystem

Option D,  it has a strong influence on the ecosystem

Explanation:

Keystone species are an essential part of an ecosystem and their functions/mark cannot be replaced by any other organism. Once the keystone species is removed from an ecosystem, the ecosystem struggles to sustain  or it changes radically. A keystone species in majority of ecosystems/food web is a predator but this is not true in all ecosystems/or with all keystone species.  

For example – there was a trophic cascade when the Gray wolves in the greater Yellowstone ecosystem were removed.  

regulation of gene expression. gene expression can be regulated by various cellular processes with the aim to control the amount and nature of the expressed genes. these regulatory proteins bind to dna and send signals that indirectly control the rate of gene expression

explanation:

answer; polycythemia is the correct answer;