What is one way that changes can occur in a dna sequence?

Why do german shepherds shed so much

Which sequence correctly shows the path of carbon dioxide during repiration?

Guinea pig coat color is determined by a single gene. the allele for black coat color is dominant to brown. in a cross between twoblack-haired guinea pigs, 20 offspring are born. if both parents were heterozygous, probability would predict that approximately howmany of the 20 offspring would have brown hair?