What type of genetic alteration results in an organism containing two different alleles for a specific gene?

The term that describes an organism containing two different alleles for a specific gene is heterozygous. In genetics, an allele is a variant form of a gene. When an individual has two different alleles at a particular gene locus, they are termed heterozygous for that gene. This genetic makeup can lead to variations in traits, as one allele may be dominant over the other, influencing the organism's phenotype (the observable characteristics).

In contrast, homozygous refers to an organism having two identical alleles for a gene, while hemizygous refers to having only one allele for a gene, often seen in males concerning X-linked traits, since they possess only one X chromosome. Nullisomic describes a condition in which an organism is missing both copies of a specific chromosome, which typically affects more than just a single gene. Understanding these definitions is crucial for distinguishing between various forms of genetic variation in organisms.