Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.

Since natural selection acts on mutations, then Genetic variation must be present in a population before natural selection can act on it. Option A is correct.

Before answering the question, let us review what mutation and natural selection are.

A mutation is a stable and hereditably change in the genetic material.

These changes alter  DNI sequences and introduce new variants.

Mutations can be damaging or beneficial.

When beneficial, mutations produce changes that help the individual adapt to an environment. These are cases in which mutations are essential to evolution.

Evolution is possible when the mutation affects the whole species.

Mutations depend on each group's environment and the ecological pressures that act on individuals and let them adapt to the environmental conditions.

Individuals carrying and expressing the mutations increase their fitness to survive and reproduce, transferring their genes to the following generations.

These mutations end by fixating.

Natural selection is an evolutive force that selects beneficial alleles and increases their frequency in the population.

Natural selection results in adaptation, meaning it causes an increase in the aptitude phenotype (fitness). It acts favoring an allele or against it, according to how it affects the fitness of individuals.

In many cases adaptations, resulting from the natural selection can be correlated to environmental factors or selective pressures applied by other organisms or habitats.

The selective agent is the environmental trait that determines the differential survival of the phenotypic classes.

According to the previous framework, we can conclude that Genetic variation can be caused by mutations. Natural selection acts on mutations, favoring them and leading them to fixation or eliminating them. The destiny of the mutation depends on how they affect the organism's fitness.

Since natural selection acts on mutations, then Genetic variation must be present in a population before natural selection can act on it. Option A is correct.

You can learn more about genetic variation at

link

link

link

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.