Final answer:
Alleles differ from each other based on variations in their nucleotide sequence, which can lead to different traits being expressed. While the terms dominant and recessive describe how these alleles are expressed, the actual difference is within the DNA sequence itself, contributing to an organism's genotype and thus its phenotype.
Step-by-step explanation:
Alleles differ from each other based on their nucleotide sequence within a gene. While it's true that some alleles are dominant whereas others are recessive, what makes them differ fundamentally is the variation in the sequence of DNA that defines them. This variation can result in distinct traits being expressed, which contribute to an organism's phenotype.
Alleles for different genes assort independently during meiosis, which is a key part of how genetic diversity is created within a species. A person's genetic makeup, known as their genotype, consists of the alleles they inherit from their parents. For instance, blood type is determined by the combination of alleles inherited for that specific gene, which could be AA, BB, OO, AB, AO, or BO.
It's important to understand that while alleles can be classified as dominant or recessive based on their expression, the core difference is coded in their DNA sequences. Moreover, genotype and phenotype are concepts central to this understanding. The genotype is an individual's specific genetic allele combination, while the phenotype is the observable manifestation of these genes.