PLEASE HELP I WILL GIVE BRAINLIEST Which of the following is correct about mutations and genetic variation?

It must be present in a population before natural selection can act upon the population.
It arises in response to changes in the environment.
It tends to be reduced when diploid organisms produce gametes and reproduce.
It is created by the direct action of natural selection.

a. It must be present in a population before natural selection can act upon the population.

Explanation:

Genetic variation is the difference in the DNA sequences in individuals, which makes a member of a species different from another member of the same species. It can also be said to be the differences in the genetic make up of individuals of a species population.

Genetic variation must be present in a species population before evolutionary mechanisms, such as evolution, can occur. Genetic variation must be present in a population of a species before natural selection can act upon the population, as natural selection can only increase or reduce the frequency of alleles present in the species population already.

Genetic variation in a population of species is important for natural selection to occur.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands