What determines whether a phenotype occurs more frequent or not in certain population?

The selection pressure for or against that phenotype and whether the phenotype increases the reproductive fitness of an organism.

Explanation:

Selection pressures would include predation and ability to find food etc. Traits such as coat colour or agility which aid animals in these tasks would favour their survival and hence be selected for in the population. Through natural selection, these phenotypes will become more frequent in the population.

Traits that improve the reproductive success such as the ability to find mate would also increase the probability of genes being passed down to their offsprings which would ultimately affect the allele frequency in the gene pool. A trait which does not affect reproductive success in humans is the human lifespan hence it can be observed that there is no selection pressure to favour people with longer lifespan. (the increase in human lifespan over the years is due to the development of healthcare and technology)

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.

answer; civil inattention;