Final answer:
Alleles are different forms of the same gene resulting in variation of traits within a species. Humans inherit two alleles for each gene, one from each parent, determining their traits. The study of single nucleotide polymorphisms (SNPs) highlights these small genetic differences.
Step-by-step explanation:
The DNA sequences, indicated by alphabetic abbreviations, are alternate forms of the same gene called alleles. An allele is a variant form of a gene, which can result in different traits, such as blood type in humans. Each person inherits two alleles for a given gene, one from each parent, and the combination of these alleles determines the individual's trait for that gene. Since DNA is a code where the sequence of bases determines the gene's identity, alleles are essentially different versions of this sequence.
For instance, the gene for blood type can have three possible sequences: A, B, and O. A person might inherit an A allele from one parent and a B allele from the other, resulting in AB blood type. The diploid nature of human cells means that both alleles can be the same (such as AA or OO) or different (such as AB or AO).
DNA sequencing and the study of single nucleotide polymorphisms (SNPs) further clarify the concept of alleles, providing insight into the small variations between the DNA sequences of individuals. An SNP, which is a difference at a single nucleotide position, can result in different alleles if the change occurs within a gene. These slight variations contribute to the diversity within a species.