Many differences in gene sequences between species, and also among individuals within a species, consist of single nucleotide polymorphisms. choose the statement that best explains why these types of differences are among the most common dna changes observed?

A single nucleotide polymorphism (SNP) is the most common gene variation found among people. A SNP represents a change in a single DNA block, called a nuecleotide, being able, for example, to replace a nucleotide cytosine (C), with a nucleotide thymine (T), guanine (G) or adenine (A) in the genome. They represent the 90% of all the human gene variations.

Explanation:

the answer is a or when it says crossing over

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).