McCance & Huether's Pathophysiology Test 1 Practice Test

Having two different alleles at a single gene means the organism is heterozygous for that gene. The genotype describes the pair of alleles present, so Aa indicates two different alleles, while AA or aa would be homozygous with identical alleles. This distinction is important because whether a trait is expressed often depends on dominance relationships: a dominant allele can mask the other in a heterozygous state, while recessive traits typically require two copies to be expressed. In contrast, the term locus refers to the gene’s position on a chromosome, introns are noncoding segments within a gene, and the genome is the entire set of genetic material.