Final answer:
Two alleles of the same gene differ due to DNA sequence differences, leading to variability in traits such as blood type. Alleles are located at the same locus on homologous chromosomes.
Step-by-step explanation:
The two alleles of the same gene differ from each other primarily due to DNA sequence differences. Therefore, the correct answer to your question is C) they have one or more DNA sequence differences. Alleles are different versions of the same gene that arise due to mutations and variations in the DNA sequence. They are found at the same location, or locus, on homologous chromosomes, but these slight variations can lead to different traits, such as blood type A, B, or O.
It is these genetic variations that contribute to the diversity within a species. For example, individuals with alleles AA, BB, or OO for blood type are homozygous, whereas individuals with AB, AO, or BO are heterozygous, showcasing the presence of different alleles. Each copy of a homologous pair of chromosomes originates from a different parent; therefore, the genes themselves are not identical. The variation of individuals within a species is due to the specific combination of the genes inherited from both parents.